[basic.exec] - C++23 → Trunk

Files changed (1) hide show

tmp/tmptyjqvlkh/{from.md → to.md} +166 -552

tmp/tmptyjqvlkh/{from.md → to.md} RENAMED Viewed

@@ -64,16 +64,18 @@ or *initializer* E are
 A *full-expression* is
 - an unevaluated operand [[expr.context]],
 - a *constant-expression* [[expr.const]],
 - an immediate invocation [[expr.const]],
-- an *init-declarator* [[dcl.decl]] or a *mem-initializer*
   [[class.base.init]], including the constituent expressions of the
   initializer,
 - an invocation of a destructor generated at the end of the lifetime of
   an object other than a temporary object [[class.temporary]] whose
-  lifetime has not been extended, or
 - an expression that is not a subexpression of another expression and
   that is not otherwise part of a full-expression.
 If a language construct is defined to produce an implicit call of a
 function, a use of the language construct is considered to be an
@@ -100,11 +102,11 @@ S s1(1);                        // full-expression comprises call of S::S(int)
 void f() {
   S s2 = 2;                     // full-expression comprises call of S::S(int)
   if (S(3).v())                 // full-expression includes lvalue-to-rvalue and int to bool conversions,
                                 // performed before temporary is deleted at end of full-expression
   { }
-  bool b = noexcept(S()); // exception specification of destructor of S considered for noexcept
   // full-expression is destruction of s2 at end of block
 }
 struct B {
   B(S = S(0));
@@ -121,19 +123,20 @@ full-expression. For example, subexpressions involved in evaluating
 default arguments [[dcl.fct.default]] are considered to be created in
 the expression that calls the function, not the expression that defines
 the default argument. — *end note*]
 Reading an object designated by a `volatile` glvalue [[basic.lval]],
-modifying an object, calling a library I/O function, or calling a
-function that does any of those operations are all *side effects*, which
-are changes in the state of the execution environment. *Evaluation* of
-an expression (or a subexpression) in general includes both value
 computations (including determining the identity of an object for
 glvalue evaluation and fetching a value previously assigned to an object
 for prvalue evaluation) and initiation of side effects. When a call to a
 library I/O function returns or an access through a volatile glvalue is
-evaluated the side effect is considered complete, even though some
 external actions implied by the call (such as the I/O itself) or by the
 `volatile` access may not have completed yet.
 *Sequenced before* is an asymmetric, transitive, pair-wise relation
 between evaluations executed by a single thread [[intro.multithread]],
@@ -158,29 +161,43 @@ every value computation and every side effect associated with the
 expression *X* is sequenced before every value computation and every
 side effect associated with the expression *Y*.
 Every value computation and side effect associated with a
 full-expression is sequenced before every value computation and side
-effect associated with the next full-expression to be evaluated.[^22]
 Except where noted, evaluations of operands of individual operators and
 of subexpressions of individual expressions are unsequenced.
 [*Note 5*: In an expression that is evaluated more than once during the
 execution of a program, unsequenced and indeterminately sequenced
 evaluations of its subexpressions need not be performed consistently in
 different evaluations. — *end note*]
 The value computations of the operands of an operator are sequenced
-before the value computation of the result of the operator. If a side
-effect on a memory location [[intro.memory]] is unsequenced relative to
-either another side effect on the same memory location or a value
-computation using the value of any object in the same memory location,
-and they are not potentially concurrent [[intro.multithread]], the
-behavior is undefined.
-[*Note 6*: The next subclause imposes similar, but more complex
 restrictions on potentially concurrent computations. — *end note*]
 [*Example 3*:
 ``` cpp
@@ -188,24 +205,35 @@ void g(int i) {
   i = 7, i++, i++;              // i becomes 9
   i = i++ + 1;                  // the value of i is incremented
   i = i++ + i;                  // undefined behavior
   i = i + 1;                    // the value of i is incremented
 }
 ```
 — *end example*]
-When invoking a function (whether or not the function is inline), every
-argument expression and the postfix expression designating the called
-function are sequenced before every expression or statement in the body
-of the called function. For each function invocation or evaluation of an
-*await-expression* *F*, each evaluation that does not occur within *F*
-but is evaluated on the same thread and as part of the same signal
-handler (if any) is either sequenced before all evaluations that occur
-within *F* or sequenced after all evaluations that occur within
-*F*;[^23]
 if *F* invokes or resumes a coroutine [[expr.await]], only evaluations
 subsequent to the previous suspension (if any) and prior to the next
 suspension (if any) are considered to occur within *F*.
@@ -224,14 +252,19 @@ regardless of the syntax of the expression that calls the function.
 If a signal handler is executed as a result of a call to the
 `std::raise` function, then the execution of the handler is sequenced
 after the invocation of the `std::raise` function and before its return.
-[*Note 7*: When a signal is received for another reason, the execution
 of the signal handler is usually unsequenced with respect to the rest of
 the program. — *end note*]
 ### Multi-threaded executions and data races <a id="intro.multithread">[[intro.multithread]]</a>
 #### General <a id="intro.multithread.general">[[intro.multithread.general]]</a>
 A *thread of execution* (also known as a *thread*) is a single flow of
@@ -241,12 +274,12 @@ subsequently executed by the thread.
 [*Note 1*: When one thread creates another, the initial call to the
 top-level function of the new thread is executed by the new thread, not
 by the creating thread. — *end note*]
-Every thread in a program can potentially access every object and
-function in a program.[^24]
 Under a hosted implementation, a C++ program can have more than one
 thread running concurrently. The execution of each thread proceeds as
 defined by the remainder of this document. The execution of the entire
 program consists of an execution of all of its threads.
@@ -274,27 +307,37 @@ below.
 Much of this subclause is motivated by the desire to support atomic
 operations with explicit and detailed visibility constraints. However,
 it also implicitly supports a simpler view for more restricted
 programs. — *end note*]
-Two expression evaluations *conflict* if one of them modifies a memory
-location [[intro.memory]] and the other one reads or modifies the same
-memory location.
 The library defines a number of atomic operations [[atomics]] and
 operations on mutexes [[thread]] that are specially identified as
 synchronization operations. These operations play a special role in
 making assignments in one thread visible to another. A synchronization
-operation on one or more memory locations is either a consume operation,
-an acquire operation, a release operation, or both an acquire and
-release operation. A synchronization operation without an associated
-memory location is a fence and can be either an acquire fence, a release
-fence, or both an acquire and release fence. In addition, there are
-relaxed atomic operations, which are not synchronization operations, and
-atomic read-modify-write operations, which have special characteristics.
-[*Note 2*: For example, a call that acquires a mutex will perform an
 acquire operation on the locations comprising the mutex.
 Correspondingly, a call that releases the same mutex will perform a
 release operation on those same locations. Informally, performing a
 release operation on A forces prior side effects on other memory
 locations to become visible to other threads that later perform a
@@ -303,11 +346,11 @@ not synchronization operations even though, like synchronization
 operations, they cannot contribute to data races. — *end note*]
 All modifications to a particular atomic object M occur in some
 particular total order, called the *modification order* of M.
-[*Note 3*: There is a separate order for each atomic object. There is
 no requirement that these can be combined into a single total order for
 all objects. In general this will be impossible since different threads
 can observe modifications to different objects in inconsistent
 orders. — *end note*]
@@ -319,181 +362,107 @@ subsequent operation is an atomic read-modify-write operation.
 Certain library calls *synchronize with* other library calls performed
 by another thread. For example, an atomic store-release synchronizes
 with a load-acquire that takes its value from the store
 [[atomics.order]].
-[*Note 4*: Except in the specified cases, reading a later value does
 not necessarily ensure visibility as described below. Such a requirement
 would sometimes interfere with efficient implementation. — *end note*]
-[*Note 5*: The specifications of the synchronization operations define
 when one reads the value written by another. For atomic objects, the
 definition is clear. All operations on a given mutex occur in a single
 total order. Each mutex acquisition “reads the value written” by the
 last mutex release. — *end note*]
-An evaluation A *carries a dependency* to an evaluation B if
-- the value of A is used as an operand of B, unless:
-  - B is an invocation of any specialization of `std::kill_dependency`
-    [[atomics.order]], or
-  - A is the left operand of a built-in logical (`&&`, see
-    [[expr.log.and]]) or logical (`||`, see  [[expr.log.or]]) operator,
-    or
-  - A is the left operand of a conditional (`?:`, see  [[expr.cond]])
-    operator, or
-  - A is the left operand of the built-in comma (`,`) operator
-    [[expr.comma]];
-  or
-- A writes a scalar object or bit-field M, B reads the value written by
-  A from M, and A is sequenced before B, or
-- for some evaluation X, A carries a dependency to X, and X carries a
-  dependency to B.
-[*Note 6*: “Carries a dependency to” is a subset of “is sequenced
-before”, and is similarly strictly intra-thread. — *end note*]
-An evaluation A is *dependency-ordered before* an evaluation B if
-- A performs a release operation on an atomic object M, and, in another
-  thread, B performs a consume operation on M and reads the value
-  written by A, or
-- for some evaluation X, A is dependency-ordered before X and X carries
-  a dependency to B.
-[*Note 7*: The relation “is dependency-ordered before” is analogous to
-“synchronizes with”, but uses release/consume in place of
-release/acquire. — *end note*]
-An evaluation A *inter-thread happens before* an evaluation B if
-- A synchronizes with B, or
-- A is dependency-ordered before B, or
-- for some evaluation X
-  - A synchronizes with X and X is sequenced before B, or
-  - A is sequenced before X and X inter-thread happens before B, or
-  - A inter-thread happens before X and X inter-thread happens before B.
-[*Note 8*: The “inter-thread happens before” relation describes
-arbitrary concatenations of “sequenced before”, “synchronizes with” and
-“dependency-ordered before” relationships, with two exceptions. The
-first exception is that a concatenation is not permitted to end with
-“dependency-ordered before” followed by “sequenced before”. The reason
-for this limitation is that a consume operation participating in a
-“dependency-ordered before” relationship provides ordering only with
-respect to operations to which this consume operation actually carries a
-dependency. The reason that this limitation applies only to the end of
-such a concatenation is that any subsequent release operation will
-provide the required ordering for a prior consume operation. The second
-exception is that a concatenation is not permitted to consist entirely
-of “sequenced before”. The reasons for this limitation are (1) to permit
-“inter-thread happens before” to be transitively closed and (2) the
-“happens before” relation, defined below, provides for relationships
-consisting entirely of “sequenced before”. — *end note*]
 An evaluation A *happens before* an evaluation B (or, equivalently, B
-*happens after* A) if:
-- A is sequenced before B, or
-- A inter-thread happens before B.
-The implementation shall ensure that no program execution demonstrates a
-cycle in the “happens before” relation.
-[*Note 9*: This cycle would otherwise be possible only through the use
-of consume operations. — *end note*]
-An evaluation A *simply happens before* an evaluation B if either
 - A is sequenced before B, or
 - A synchronizes with B, or
-- A simply happens before X and X simply happens before B.
-[*Note 10*: In the absence of consume operations, the happens before
-and simply happens before relations are identical. — *end note*]
 An evaluation A *strongly happens before* an evaluation D if, either
 - A is sequenced before D, or
 - A synchronizes with D, and both A and D are sequentially consistent
   atomic operations [[atomics.order]], or
 - there are evaluations B and C such that A is sequenced before B, B
- simply happens before C, and C is sequenced before D, or
 - there is an evaluation B such that A strongly happens before B, and B
   strongly happens before D.
-[*Note 11*: Informally, if A strongly happens before B, then A appears
-to be evaluated before B in all contexts. Strongly happens before
-excludes consume operations. — *end note*]
 A *visible side effect* A on a scalar object or bit-field M with respect
 to a value computation B of M satisfies the conditions:
 - A happens before B and
 - there is no other side effect X to M such that A happens before X and
   X happens before B.
 The value of a non-atomic scalar object or bit-field M, as determined by
-evaluation B, shall be the value stored by the visible side effect A.
-[*Note 12*: If there is ambiguity about which side effect to a
 non-atomic object or bit-field is visible, then the behavior is either
 unspecified or undefined. — *end note*]
-[*Note 13*: This states that operations on ordinary objects are not
 visibly reordered. This is not actually detectable without data races,
-but it is necessary to ensure that data races, as defined below, and
-with suitable restrictions on the use of atomics, correspond to data
-races in a simple interleaved (sequentially consistent)
-execution. — *end note*]
-The value of an atomic object M, as determined by evaluation B, shall be
-the value stored by some side effect A that modifies M, where B does not
-happen before A.
-[*Note 14*: The set of such side effects is also restricted by the rest
 of the rules described here, and in particular, by the coherence
 requirements below. — *end note*]
 If an operation A that modifies an atomic object M happens before an
-operation B that modifies M, then A shall be earlier than B in the
 modification order of M.
-[*Note 15*: This requirement is known as write-write
 coherence. — *end note*]
 If a value computation A of an atomic object M happens before a value
 computation B of M, and A takes its value from a side effect X on M,
-then the value computed by B shall either be the value stored by X or
-the value stored by a side effect Y on M, where Y follows X in the
 modification order of M.
-[*Note 16*: This requirement is known as read-read
 coherence. — *end note*]
 If a value computation A of an atomic object M happens before an
-operation B that modifies M, then A shall take its value from a side
-effect X on M, where X precedes B in the modification order of M.
-[*Note 17*: This requirement is known as read-write
 coherence. — *end note*]
 If a side effect X on an atomic object M happens before a value
-computation B of M, then the evaluation B shall take its value from X or
-from a side effect Y that follows X in the modification order of M.
-[*Note 18*: This requirement is known as write-read
 coherence. — *end note*]
-[*Note 19*: The four preceding coherence requirements effectively
 disallow compiler reordering of atomic operations to a single object,
 even if both operations are relaxed loads. This effectively makes the
 cache coherence guarantee provided by most hardware available to C++
 atomic operations. — *end note*]
-[*Note 20*: The value observed by a load of an atomic depends on the
 “happens before” relation, which depends on the values observed by loads
 of atomics. The intended reading is that there must exist an association
 of atomic loads with modifications they observe that, together with
 suitably chosen modification orders and the “happens before” relation
 derived as described above, satisfy the resulting constraints as imposed
@@ -509,67 +478,71 @@ The execution of a program contains a *data race* if it contains two
 potentially concurrent conflicting actions, at least one of which is not
 atomic, and neither happens before the other, except for the special
 case for signal handlers described below. Any such data race results in
 undefined behavior.
-[*Note 21*: It can be shown that programs that correctly use mutexes
 and `memory_order::seq_cst` operations to prevent all data races and use
 no other synchronization operations behave as if the operations executed
 by their constituent threads were simply interleaved, with each value
 computation of an object being taken from the last side effect on that
 object in that interleaving. This is normally referred to as “sequential
 consistency”. However, this applies only to data-race-free programs, and
 data-race-free programs cannot observe most program transformations that
 do not change single-threaded program semantics. In fact, most
-single-threaded program transformations continue to be allowed, since
-any program that behaves differently as a result has undefined
 behavior. — *end note*]
-Two accesses to the same object of type `volatile std::sig_atomic_t` do
-not result in a data race if both occur in the same thread, even if one
-or more occurs in a signal handler. For each signal handler invocation,
-evaluations performed by the thread invoking a signal handler can be
-divided into two groups A and B, such that no evaluations in B happen
-before evaluations in A, and the evaluations of such
-`volatile std::sig_atomic_t` objects take values as though all
-evaluations in A happened before the execution of the signal handler and
-the execution of the signal handler happened before all evaluations in
-B.
-[*Note 22*: Compiler transformations that introduce assignments to a
 potentially shared memory location that would not be modified by the
 abstract machine are generally precluded by this document, since such an
 assignment might overwrite another assignment by a different thread in
 cases in which an abstract machine execution would not have encountered
 a data race. This includes implementations of data member assignment
 that overwrite adjacent members in separate memory locations. Reordering
 of atomic loads in cases in which the atomics in question might alias is
 also generally precluded, since this could violate the coherence
 rules. — *end note*]
-[*Note 23*: Transformations that introduce a speculative read of a
-potentially shared memory location might not preserve the semantics of
-the C++ program as defined in this document, since they potentially
-introduce a data race. However, they are typically valid in the context
-of an optimizing compiler that targets a specific machine with
-well-defined semantics for data races. They would be invalid for a
 hypothetical machine that is not tolerant of races or provides hardware
 race detection. — *end note*]
 #### Forward progress <a id="intro.progress">[[intro.progress]]</a>
 The implementation may assume that any thread will eventually do one of
 the following:
 - terminate,
 - make a call to a library I/O function,
-- perform an access through a volatile glvalue, or
-- perform a synchronization operation or an atomic operation.
 [*Note 1*: This is intended to allow compiler transformations such as
-removal of empty loops, even when termination cannot be
-proven. — *end note*]
 Executions of atomic functions that are either defined to be lock-free
 [[atomics.flag]] or indicated as lock-free [[atomics.lockfree]] are
 *lock-free executions*.
@@ -593,13 +566,14 @@ Executions of atomic functions that are either defined to be lock-free
 During the execution of a thread of execution, each of the following is
 termed an *execution step*:
 - termination of the thread of execution,
-- performing an access through a volatile glvalue, or
-- completion of a call to a library I/O function, a synchronization
-  operation, or an atomic operation.
 An invocation of a standard library function that blocks [[defns.block]]
 is considered to continuously execute execution steps while waiting for
 the condition that it blocks on to be satisfied.
@@ -621,12 +595,12 @@ concurrent threads that are not blocked in a standard library function
 For a thread of execution providing *concurrent forward progress
 guarantees*, the implementation ensures that the thread will eventually
 make progress for as long as it has not terminated.
-[*Note 5*: This is required regardless of whether or not other threads
-of execution (if any) have been or are making progress. To eventually
 fulfill this requirement means that this will happen in an unspecified
 but finite amount of time. — *end note*]
 It is *implementation-defined* whether the implementation-created thread
 of execution that executes `main` [[basic.start.main]] and the threads
@@ -739,24 +713,24 @@ function parameter is called `argv`, where `argc` shall be the number of
 arguments passed to the program from the environment in which the
 program is run. If `argc` is nonzero these arguments shall be supplied
 in `argv[0]` through `argv[argc - 1]` as pointers to the initial
 characters of null-terminated multibyte strings (NTMBSs)
 [[multibyte.strings]] and `argv[0]` shall be the pointer to the initial
-character of a NTMBS that represents the name used to invoke the program
-or `""`. The value of `argc` shall be non-negative. The value of
 `argv[argc]` shall be 0.
 *Recommended practice:* Any further (optional) parameters should be
 added after `argv`.
-The function `main` shall not be used within a program. The linkage
 [[basic.link]] of `main` is *implementation-defined*. A program that
 defines `main` as deleted or that declares `main` to be `inline`,
 `static`, `constexpr`, or `consteval` is ill-formed. The function `main`
 shall not be a coroutine [[dcl.fct.def.coroutine]]. The `main` function
-shall not be declared with a *linkage-specification* [[dcl.link]]. A
-program that declares
 - a variable `main` that belongs to the global scope, or
 - a function `main` that belongs to the global scope and is attached to
   a named module, or
 - a function template `main` that belongs to the global scope, or
@@ -772,29 +746,29 @@ calling the function `std::exit(int)` [[support.start.term]]) does not
 destroy any objects with automatic storage duration [[class.dtor]]. If
 `std::exit` is invoked during the destruction of an object with static
 or thread storage duration, the program has undefined behavior.
 A `return` statement [[stmt.return]] in `main` has the effect of leaving
-the main function (destroying any objects with automatic storage
-duration) and calling `std::exit` with the return value as the argument.
-If control flows off the end of the *compound-statement* of `main`, the
-effect is equivalent to a `return` with operand `0` (see also
-[[except.handle]]).
 #### Static initialization <a id="basic.start.static">[[basic.start.static]]</a>
 Variables with static storage duration are initialized as a consequence
 of program initiation. Variables with thread storage duration are
 initialized as a consequence of thread execution. Within each of these
 phases of initiation, initialization occurs as follows.
-*Constant initialization* is performed if a variable or temporary object
-with static or thread storage duration is constant-initialized
-[[expr.const]]. If constant initialization is not performed, a variable
-with static storage duration [[basic.stc.static]] or thread storage
-duration [[basic.stc.thread]] is zero-initialized [[dcl.init]].
-Together, zero-initialization and constant initialization are called
 *static initialization*; all other initialization is
 *dynamic initialization*. All static initialization strongly happens
 before [[intro.races]] any dynamic initialization.
 [*Note 1*: The dynamic initialization of non-block variables is
@@ -887,11 +861,11 @@ thread storage duration variable.
 It is *implementation-defined* whether the dynamic initialization of a
 non-block non-inline variable with static storage duration is sequenced
 before the first statement of `main` or is deferred. If it is deferred,
 it strongly happens before any non-initialization odr-use of any
 non-inline function or non-inline variable defined in the same
-translation unit as the variable to be initialized.[^25]
 It is *implementation-defined* in which threads and at which points in
 the program such deferred dynamic initialization occurs.
 *Recommended practice:* An implementation should choose such points in a
@@ -1027,365 +1001,5 @@ static-storage-duration objects. — *end note*]
 Calling the function `std::abort()` declared in `<cstdlib>` terminates
 the program without executing any destructors and without calling the
 functions passed to `std::atexit()` or `std::at_quick_exit()`.
-<!-- Link reference definitions -->
-[allocator.members]: mem.md#allocator.members
-[allocator.traits.members]: mem.md#allocator.traits.members
-[atomics]: thread.md#atomics
-[atomics.flag]: thread.md#atomics.flag
-[atomics.lockfree]: thread.md#atomics.lockfree
-[atomics.order]: thread.md#atomics.order
-[bad.alloc]: support.md#bad.alloc
-[basic]: #basic
-[basic.align]: #basic.align
-[basic.compound]: #basic.compound
-[basic.def]: #basic.def
-[basic.def.odr]: #basic.def.odr
-[basic.exec]: #basic.exec
-[basic.extended.fp]: #basic.extended.fp
-[basic.fundamental]: #basic.fundamental
-[basic.fundamental.width]: #basic.fundamental.width
-[basic.indet]: #basic.indet
-[basic.life]: #basic.life
-[basic.link]: #basic.link
-[basic.lookup]: #basic.lookup
-[basic.lookup.argdep]: #basic.lookup.argdep
-[basic.lookup.elab]: #basic.lookup.elab
-[basic.lookup.general]: #basic.lookup.general
-[basic.lookup.qual]: #basic.lookup.qual
-[basic.lookup.qual.general]: #basic.lookup.qual.general
-[basic.lookup.udir]: #basic.lookup.udir
-[basic.lookup.unqual]: #basic.lookup.unqual
-[basic.lval]: expr.md#basic.lval
-[basic.memobj]: #basic.memobj
-[basic.namespace]: dcl.md#basic.namespace
-[basic.pre]: #basic.pre
-[basic.scope]: #basic.scope
-[basic.scope.block]: #basic.scope.block
-[basic.scope.class]: #basic.scope.class
-[basic.scope.enum]: #basic.scope.enum
-[basic.scope.lambda]: #basic.scope.lambda
-[basic.scope.namespace]: #basic.scope.namespace
-[basic.scope.param]: #basic.scope.param
-[basic.scope.pdecl]: #basic.scope.pdecl
-[basic.scope.scope]: #basic.scope.scope
-[basic.scope.temp]: #basic.scope.temp
-[basic.start]: #basic.start
-[basic.start.dynamic]: #basic.start.dynamic
-[basic.start.main]: #basic.start.main
-[basic.start.static]: #basic.start.static
-[basic.start.term]: #basic.start.term
-[basic.stc]: #basic.stc
-[basic.stc.auto]: #basic.stc.auto
-[basic.stc.dynamic]: #basic.stc.dynamic
-[basic.stc.dynamic.allocation]: #basic.stc.dynamic.allocation
-[basic.stc.dynamic.deallocation]: #basic.stc.dynamic.deallocation
-[basic.stc.dynamic.general]: #basic.stc.dynamic.general
-[basic.stc.general]: #basic.stc.general
-[basic.stc.inherit]: #basic.stc.inherit
-[basic.stc.static]: #basic.stc.static
-[basic.stc.thread]: #basic.stc.thread
-[basic.type.qualifier]: #basic.type.qualifier
-[basic.type.qualifier.rel]: #basic.type.qualifier.rel
-[basic.types]: #basic.types
-[basic.types.general]: #basic.types.general
-[bit.cast]: utilities.md#bit.cast
-[c.malloc]: mem.md#c.malloc
-[class]: class.md#class
-[class.abstract]: class.md#class.abstract
-[class.access]: class.md#class.access
-[class.access.base]: class.md#class.access.base
-[class.base.init]: class.md#class.base.init
-[class.bit]: class.md#class.bit
-[class.cdtor]: class.md#class.cdtor
-[class.conv.fct]: class.md#class.conv.fct
-[class.copy.assign]: class.md#class.copy.assign
-[class.copy.ctor]: class.md#class.copy.ctor
-[class.copy.elision]: class.md#class.copy.elision
-[class.default.ctor]: class.md#class.default.ctor
-[class.derived]: class.md#class.derived
-[class.dtor]: class.md#class.dtor
-[class.free]: class.md#class.free
-[class.friend]: class.md#class.friend
-[class.mem]: class.md#class.mem
-[class.member.lookup]: #class.member.lookup
-[class.mfct]: class.md#class.mfct
-[class.mfct.non.static]: class.md#class.mfct.non.static
-[class.name]: class.md#class.name
-[class.pre]: class.md#class.pre
-[class.prop]: class.md#class.prop
-[class.qual]: #class.qual
-[class.spaceship]: class.md#class.spaceship
-[class.static]: class.md#class.static
-[class.static.data]: class.md#class.static.data
-[class.temporary]: #class.temporary
-[class.union]: class.md#class.union
-[class.union.anon]: class.md#class.union.anon
-[class.virtual]: class.md#class.virtual
-[conv]: expr.md#conv
-[conv.array]: expr.md#conv.array
-[conv.func]: expr.md#conv.func
-[conv.integral]: expr.md#conv.integral
-[conv.lval]: expr.md#conv.lval
-[conv.mem]: expr.md#conv.mem
-[conv.prom]: expr.md#conv.prom
-[conv.ptr]: expr.md#conv.ptr
-[conv.rank]: #conv.rank
-[conv.rval]: expr.md#conv.rval
-[cpp.predefined]: cpp.md#cpp.predefined
-[cstddef.syn]: support.md#cstddef.syn
-[cstring.syn]: strings.md#cstring.syn
-[dcl.align]: dcl.md#dcl.align
-[dcl.array]: dcl.md#dcl.array
-[dcl.attr]: dcl.md#dcl.attr
-[dcl.attr.nouniqueaddr]: dcl.md#dcl.attr.nouniqueaddr
-[dcl.constexpr]: dcl.md#dcl.constexpr
-[dcl.dcl]: dcl.md#dcl.dcl
-[dcl.decl]: dcl.md#dcl.decl
-[dcl.enum]: dcl.md#dcl.enum
-[dcl.fct]: dcl.md#dcl.fct
-[dcl.fct.def]: dcl.md#dcl.fct.def
-[dcl.fct.def.coroutine]: dcl.md#dcl.fct.def.coroutine
-[dcl.fct.def.general]: dcl.md#dcl.fct.def.general
-[dcl.fct.default]: dcl.md#dcl.fct.default
-[dcl.init]: dcl.md#dcl.init
-[dcl.init.aggr]: dcl.md#dcl.init.aggr
-[dcl.init.list]: dcl.md#dcl.init.list
-[dcl.init.ref]: dcl.md#dcl.init.ref
-[dcl.link]: dcl.md#dcl.link
-[dcl.meaning]: dcl.md#dcl.meaning
-[dcl.mptr]: dcl.md#dcl.mptr
-[dcl.name]: dcl.md#dcl.name
-[dcl.pre]: dcl.md#dcl.pre
-[dcl.ptr]: dcl.md#dcl.ptr
-[dcl.ref]: dcl.md#dcl.ref
-[dcl.spec]: dcl.md#dcl.spec
-[dcl.spec.auto]: dcl.md#dcl.spec.auto
-[dcl.stc]: dcl.md#dcl.stc
-[dcl.struct.bind]: dcl.md#dcl.struct.bind
-[dcl.type.decltype]: dcl.md#dcl.type.decltype
-[dcl.type.elab]: dcl.md#dcl.type.elab
-[dcl.typedef]: dcl.md#dcl.typedef
-[defns.block]: intro.md#defns.block
-[depr.local]: future.md#depr.local
-[depr.static.constexpr]: future.md#depr.static.constexpr
-[diff.cpp11.basic]: compatibility.md#diff.cpp11.basic
-[enum.udecl]: dcl.md#enum.udecl
-[except.handle]: except.md#except.handle
-[except.pre]: except.md#except.pre
-[except.spec]: except.md#except.spec
-[except.terminate]: except.md#except.terminate
-[except.throw]: except.md#except.throw
-[expr.add]: expr.md#expr.add
-[expr.alignof]: expr.md#expr.alignof
-[expr.arith.conv]: expr.md#expr.arith.conv
-[expr.ass]: expr.md#expr.ass
-[expr.await]: expr.md#expr.await
-[expr.call]: expr.md#expr.call
-[expr.cast]: expr.md#expr.cast
-[expr.comma]: expr.md#expr.comma
-[expr.cond]: expr.md#expr.cond
-[expr.const]: expr.md#expr.const
-[expr.const.cast]: expr.md#expr.const.cast
-[expr.context]: expr.md#expr.context
-[expr.delete]: expr.md#expr.delete
-[expr.dynamic.cast]: expr.md#expr.dynamic.cast
-[expr.eq]: expr.md#expr.eq
-[expr.log.and]: expr.md#expr.log.and
-[expr.log.or]: expr.md#expr.log.or
-[expr.mptr.oper]: expr.md#expr.mptr.oper
-[expr.new]: expr.md#expr.new
-[expr.pre]: expr.md#expr.pre
-[expr.prim.id]: expr.md#expr.prim.id
-[expr.prim.id.qual]: expr.md#expr.prim.id.qual
-[expr.prim.id.unqual]: expr.md#expr.prim.id.unqual
-[expr.prim.lambda]: expr.md#expr.prim.lambda
-[expr.prim.lambda.capture]: expr.md#expr.prim.lambda.capture
-[expr.prim.lambda.closure]: expr.md#expr.prim.lambda.closure
-[expr.prim.this]: expr.md#expr.prim.this
-[expr.prop]: expr.md#expr.prop
-[expr.ref]: expr.md#expr.ref
-[expr.reinterpret.cast]: expr.md#expr.reinterpret.cast
-[expr.rel]: expr.md#expr.rel
-[expr.sizeof]: expr.md#expr.sizeof
-[expr.static.cast]: expr.md#expr.static.cast
-[expr.sub]: expr.md#expr.sub
-[expr.type.conv]: expr.md#expr.type.conv
-[expr.typeid]: expr.md#expr.typeid
-[expr.unary.op]: expr.md#expr.unary.op
-[get.new.handler]: support.md#get.new.handler
-[headers]: library.md#headers
-[intro.execution]: #intro.execution
-[intro.memory]: #intro.memory
-[intro.multithread]: #intro.multithread
-[intro.multithread.general]: #intro.multithread.general
-[intro.object]: #intro.object
-[intro.progress]: #intro.progress
-[intro.races]: #intro.races
-[lex.charset]: lex.md#lex.charset
-[lex.fcon]: lex.md#lex.fcon
-[lex.name]: lex.md#lex.name
-[lex.separate]: lex.md#lex.separate
-[module.context]: module.md#module.context
-[module.global.frag]: module.md#module.global.frag
-[module.interface]: module.md#module.interface
-[module.reach]: module.md#module.reach
-[module.unit]: module.md#module.unit
-[multibyte.strings]: library.md#multibyte.strings
-[namespace.def]: dcl.md#namespace.def
-[namespace.qual]: #namespace.qual
-[namespace.udecl]: dcl.md#namespace.udecl
-[namespace.udir]: dcl.md#namespace.udir
-[namespace.unnamed]: dcl.md#namespace.unnamed
-[new.delete]: support.md#new.delete
-[new.delete.array]: support.md#new.delete.array
-[new.delete.placement]: support.md#new.delete.placement
-[new.delete.single]: support.md#new.delete.single
-[new.handler]: support.md#new.handler
-[new.syn]: support.md#new.syn
-[obj.lifetime]: mem.md#obj.lifetime
-[over]: over.md#over
-[over.literal]: over.md#over.literal
-[over.match]: over.md#over.match
-[over.match.funcs]: over.md#over.match.funcs
-[over.oper]: over.md#over.oper
-[over.over]: over.md#over.over
-[ptr.align]: mem.md#ptr.align
-[ptr.launder]: support.md#ptr.launder
-[replacement.functions]: library.md#replacement.functions
-[special]: class.md#special
-[std.modules]: library.md#std.modules
-[stdfloat.syn]: support.md#stdfloat.syn
-[stmt.block]: stmt.md#stmt.block
-[stmt.dcl]: stmt.md#stmt.dcl
-[stmt.expr]: stmt.md#stmt.expr
-[stmt.if]: stmt.md#stmt.if
-[stmt.iter]: stmt.md#stmt.iter
-[stmt.pre]: stmt.md#stmt.pre
-[stmt.ranged]: stmt.md#stmt.ranged
-[stmt.return]: stmt.md#stmt.return
-[stmt.select]: stmt.md#stmt.select
-[support.dynamic]: support.md#support.dynamic
-[support.runtime]: support.md#support.runtime
-[support.start.term]: support.md#support.start.term
-[support.types]: support.md#support.types
-[temp.concept]: temp.md#temp.concept
-[temp.deduct.guide]: temp.md#temp.deduct.guide
-[temp.dep]: temp.md#temp.dep
-[temp.dep.candidate]: temp.md#temp.dep.candidate
-[temp.dep.constexpr]: temp.md#temp.dep.constexpr
-[temp.dep.type]: temp.md#temp.dep.type
-[temp.expl.spec]: temp.md#temp.expl.spec
-[temp.explicit]: temp.md#temp.explicit
-[temp.friend]: temp.md#temp.friend
-[temp.local]: temp.md#temp.local
-[temp.names]: temp.md#temp.names
-[temp.over]: temp.md#temp.over
-[temp.over.link]: temp.md#temp.over.link
-[temp.param]: temp.md#temp.param
-[temp.point]: temp.md#temp.point
-[temp.pre]: temp.md#temp.pre
-[temp.res]: temp.md#temp.res
-[temp.spec]: temp.md#temp.spec
-[temp.spec.partial]: temp.md#temp.spec.partial
-[temp.type]: temp.md#temp.type
-[term.incomplete.type]: #term.incomplete.type
-[term.odr.use]: #term.odr.use
-[term.unevaluated.operand]: expr.md#term.unevaluated.operand
-[thread]: thread.md#thread
-[thread.jthread.class]: thread.md#thread.jthread.class
-[thread.thread.class]: thread.md#thread.thread.class
-[thread.threads]: thread.md#thread.threads
-[^1]: Appearing inside the brace-enclosed *declaration-seq* in a
-    *linkage-specification* does not affect whether a declaration is a
-    definition.
-[^2]: An implementation is not required to call allocation and
-    deallocation functions from constructors or destructors; however,
-    this is a permissible implementation technique.
-[^3]: An implicit object parameter [[over.match.funcs]] is not part of
-    the parameter-type-list.
-[^4]: Lookups in which function names are ignored include names
-    appearing in a *nested-name-specifier*, an
-    *elaborated-type-specifier*, or a *base-specifier*.
-[^5]: Unicode® is a registered trademark of Unicode, Inc. This
-    information is given for the convenience of users of this document
-    and does not constitute an endorsement by ISO or IEC of this
-    product.
-[^6]: The number of bits in a byte is reported by the macro `CHAR_BIT`
-    in the header `<climits>`.
-[^7]: Under the “as-if” rule an implementation is allowed to store two
-    objects at the same machine address or not store an object at all if
-    the program cannot observe the difference [[intro.execution]].
-[^8]: For example, before the dynamic initialization of an object with
-    static storage duration [[basic.start.dynamic]].
-[^9]: That is, an object for which a destructor will be called
-    implicitly—upon exit from the block for an object with automatic
-    storage duration, upon exit from the thread for an object with
-    thread storage duration, or upon exit from the program for an object
-    with static storage duration.
-[^10]: Some implementations might define that copying an invalid pointer
-    value causes a system-generated runtime fault.
-[^11]: The intent is to have `operator new()` implementable by calling
-    `std::malloc()` or `std::calloc()`, so the rules are substantially
-    the same. C++ differs from C in requiring a zero request to return a
-    non-null pointer.
-[^12]: The global `operator delete(void*, std::size_t)` precludes use of
-    an allocation function `void operator new(std::size_t, std::size_t)`
-    as a placement allocation function [[diff.cpp11.basic]].
-[^13]: The same rules apply to initialization of an `initializer_list`
-    object [[dcl.init.list]] with its underlying temporary array.
-[^14]: By using, for example, the library functions [[headers]]
-    `std::memcpy` or `std::memmove`.
-[^15]: By using, for example, the library functions [[headers]]
-    `std::memcpy` or `std::memmove`.
-[^16]: The intent is that the memory model of C++ is compatible with
-    that of ISO/IEC 9899 Programming Language C.
-[^17]: The size and layout of an instance of an incompletely-defined
-    object type is unknown.
-[^18]: This is also known as two’s complement representation.
-[^19]: Static class members are objects or functions, and pointers to
-    them are ordinary pointers to objects or functions.
-[^20]: For an object that is not within its lifetime, this is the first
-    byte in memory that it will occupy or used to occupy.
-[^21]: The same representation and alignment requirements are meant to
-    imply interchangeability as arguments to functions, return values
-    from functions, and non-static data members of unions.
-[^22]: As specified in  [[class.temporary]], after a full-expression is
-    evaluated, a sequence of zero or more invocations of destructor
-    functions for temporary objects takes place, usually in reverse
-    order of the construction of each temporary object.
-[^23]: In other words, function executions do not interleave with each
-    other.
-[^24]: An object with automatic or thread storage duration [[basic.stc]]
-    is associated with one specific thread, and can be accessed by a
-    different thread only indirectly through a pointer or reference
-    [[basic.compound]].
-[^25]: A non-block variable with static storage duration having
-    initialization with side effects is initialized in this case, even
-    if it is not itself odr-used [[term.odr.use]], [[basic.stc.static]].

 A *full-expression* is
 - an unevaluated operand [[expr.context]],
 - a *constant-expression* [[expr.const]],
 - an immediate invocation [[expr.const]],
+- an *init-declarator* [[dcl.decl]] (including such introduced by a
+  structured binding [[dcl.struct.bind]]) or a *mem-initializer*
   [[class.base.init]], including the constituent expressions of the
   initializer,
 - an invocation of a destructor generated at the end of the lifetime of
   an object other than a temporary object [[class.temporary]] whose
+  lifetime has not been extended,
+- the predicate of a contract assertion [[basic.contract]], or
 - an expression that is not a subexpression of another expression and
   that is not otherwise part of a full-expression.
 If a language construct is defined to produce an implicit call of a
 function, a use of the language construct is considered to be an
 void f() {
   S s2 = 2;                     // full-expression comprises call of S::S(int)
   if (S(3).v())                 // full-expression includes lvalue-to-rvalue and int to bool conversions,
                                 // performed before temporary is deleted at end of full-expression
   { }
+  bool b = noexcept(S(4)); // exception specification of destructor of S considered for noexcept
   // full-expression is destruction of s2 at end of block
 }
 struct B {
   B(S = S(0));
 default arguments [[dcl.fct.default]] are considered to be created in
 the expression that calls the function, not the expression that defines
 the default argument. — *end note*]
 Reading an object designated by a `volatile` glvalue [[basic.lval]],
+modifying an object, producing an injected declaration [[expr.const]],
+calling a library I/O function, or calling a function that does any of
+those operations are all *side effects*, which are changes in the state
+of the execution or translation environment. *Evaluation* of an
+expression (or a subexpression) in general includes both value
 computations (including determining the identity of an object for
 glvalue evaluation and fetching a value previously assigned to an object
 for prvalue evaluation) and initiation of side effects. When a call to a
 library I/O function returns or an access through a volatile glvalue is
+evaluated, the side effect is considered complete, even though some
 external actions implied by the call (such as the I/O itself) or by the
 `volatile` access may not have completed yet.
 *Sequenced before* is an asymmetric, transitive, pair-wise relation
 between evaluations executed by a single thread [[intro.multithread]],
 expression *X* is sequenced before every value computation and every
 side effect associated with the expression *Y*.
 Every value computation and side effect associated with a
 full-expression is sequenced before every value computation and side
+effect associated with the next full-expression to be evaluated.[^21]
 Except where noted, evaluations of operands of individual operators and
 of subexpressions of individual expressions are unsequenced.
 [*Note 5*: In an expression that is evaluated more than once during the
 execution of a program, unsequenced and indeterminately sequenced
 evaluations of its subexpressions need not be performed consistently in
 different evaluations. — *end note*]
 The value computations of the operands of an operator are sequenced
+before the value computation of the result of the operator. The behavior
+is undefined if
+- a side effect on a memory location [[intro.memory]] or
+- starting or ending the lifetime of an object in a memory location
+is unsequenced relative to
+- another side effect on the same memory location,
+- starting or ending the lifetime of an object occupying storage that
+  overlaps with the memory location, or
+- a value computation using the value of any object in the same memory
+  location,
+and the two evaluations are not potentially concurrent
+[[intro.multithread]].
+[*Note 6*: Starting the lifetime of an object in a memory location can
+end the lifetime of objects in other memory locations
+[[basic.life]]. — *end note*]
+[*Note 7*: The next subclause imposes similar, but more complex
 restrictions on potentially concurrent computations. — *end note*]
 [*Example 3*:
 ``` cpp
   i = 7, i++, i++;              // i becomes 9
   i = i++ + 1;                  // the value of i is incremented
   i = i++ + i;                  // undefined behavior
   i = i + 1;                    // the value of i is incremented
+  union U { int x, y; } u;
+  (u.x = 1, 0) + (u.y = 2, 0);  // undefined behavior
 }
 ```
 — *end example*]
+When invoking a function *f* (whether or not the function is inline),
+every argument expression and the postfix expression designating *f* are
+sequenced before every precondition assertion of *f*
+[[dcl.contract.func]], which in turn are sequenced before every
+expression or statement in the body of *f*, which in turn are sequenced
+before every postcondition assertion of *f*.
+For each
+- function invocation,
+- evaluation of an *await-expression* [[expr.await]], or
+- evaluation of a *throw-expression* [[expr.throw]]
+*F*, each evaluation that does not occur within *F* but is evaluated on
+the same thread and as part of the same signal handler (if any) is
+either sequenced before all evaluations that occur within *F* or
+sequenced after all evaluations that occur within *F*;[^22]
 if *F* invokes or resumes a coroutine [[expr.await]], only evaluations
 subsequent to the previous suspension (if any) and prior to the next
 suspension (if any) are considered to occur within *F*.
 If a signal handler is executed as a result of a call to the
 `std::raise` function, then the execution of the handler is sequenced
 after the invocation of the `std::raise` function and before its return.
+[*Note 8*: When a signal is received for another reason, the execution
 of the signal handler is usually unsequenced with respect to the rest of
 the program. — *end note*]
+During the evaluation of an expression as a core constant expression
+[[expr.const]], evaluations of operands of individual operators and of
+subexpressions of individual expressions that are otherwise either
+unsequenced or indeterminately sequenced are evaluated in lexical order.
 ### Multi-threaded executions and data races <a id="intro.multithread">[[intro.multithread]]</a>
 #### General <a id="intro.multithread.general">[[intro.multithread.general]]</a>
 A *thread of execution* (also known as a *thread*) is a single flow of
 [*Note 1*: When one thread creates another, the initial call to the
 top-level function of the new thread is executed by the new thread, not
 by the creating thread. — *end note*]
+Every thread in a program can potentially use every object and function
+in a program.[^23]
 Under a hosted implementation, a C++ program can have more than one
 thread running concurrently. The execution of each thread proceeds as
 defined by the remainder of this document. The execution of the entire
 program consists of an execution of all of its threads.
 Much of this subclause is motivated by the desire to support atomic
 operations with explicit and detailed visibility constraints. However,
 it also implicitly supports a simpler view for more restricted
 programs. — *end note*]
+Two expression evaluations *conflict* if one of them
+- modifies [[defns.access]] a memory location [[intro.memory]] or
+- starts or ends the lifetime of an object in a memory location
+and the other one
+- reads or modifies the same memory location or
+- starts or ends the lifetime of an object occupying storage that
+  overlaps with the memory location.
+[*Note 2*: A modification can still conflict even if it does not alter
+the value of any bits. — *end note*]
 The library defines a number of atomic operations [[atomics]] and
 operations on mutexes [[thread]] that are specially identified as
 synchronization operations. These operations play a special role in
 making assignments in one thread visible to another. A synchronization
+operation on one or more memory locations is either an acquire
+operation, a release operation, or both an acquire and release
+operation. A synchronization operation without an associated memory
+location is a fence and can be either an acquire fence, a release fence,
+or both an acquire and release fence. In addition, there are relaxed
+atomic operations, which are not synchronization operations, and atomic
+read-modify-write operations, which have special characteristics.
+[*Note 3*: For example, a call that acquires a mutex will perform an
 acquire operation on the locations comprising the mutex.
 Correspondingly, a call that releases the same mutex will perform a
 release operation on those same locations. Informally, performing a
 release operation on A forces prior side effects on other memory
 locations to become visible to other threads that later perform a
 operations, they cannot contribute to data races. — *end note*]
 All modifications to a particular atomic object M occur in some
 particular total order, called the *modification order* of M.
+[*Note 4*: There is a separate order for each atomic object. There is
 no requirement that these can be combined into a single total order for
 all objects. In general this will be impossible since different threads
 can observe modifications to different objects in inconsistent
 orders. — *end note*]
 Certain library calls *synchronize with* other library calls performed
 by another thread. For example, an atomic store-release synchronizes
 with a load-acquire that takes its value from the store
 [[atomics.order]].
+[*Note 5*: Except in the specified cases, reading a later value does
 not necessarily ensure visibility as described below. Such a requirement
 would sometimes interfere with efficient implementation. — *end note*]
+[*Note 6*: The specifications of the synchronization operations define
 when one reads the value written by another. For atomic objects, the
 definition is clear. All operations on a given mutex occur in a single
 total order. Each mutex acquisition “reads the value written” by the
 last mutex release. — *end note*]
 An evaluation A *happens before* an evaluation B (or, equivalently, B
+happens after A) if either
 - A is sequenced before B, or
 - A synchronizes with B, or
+- A happens before X and X happens before B.
+[*Note 7*: An evaluation does not happen before itself. — *end note*]
 An evaluation A *strongly happens before* an evaluation D if, either
 - A is sequenced before D, or
 - A synchronizes with D, and both A and D are sequentially consistent
   atomic operations [[atomics.order]], or
 - there are evaluations B and C such that A is sequenced before B, B
+  happens before C, and C is sequenced before D, or
 - there is an evaluation B such that A strongly happens before B, and B
   strongly happens before D.
+[*Note 8*: Informally, if A strongly happens before B, then A appears
+to be evaluated before B in all contexts. — *end note*]
 A *visible side effect* A on a scalar object or bit-field M with respect
 to a value computation B of M satisfies the conditions:
 - A happens before B and
 - there is no other side effect X to M such that A happens before X and
   X happens before B.
 The value of a non-atomic scalar object or bit-field M, as determined by
+evaluation B, is the value stored by the visible side effect A.
+[*Note 9*: If there is ambiguity about which side effect to a
 non-atomic object or bit-field is visible, then the behavior is either
 unspecified or undefined. — *end note*]
+[*Note 10*: This states that operations on ordinary objects are not
 visibly reordered. This is not actually detectable without data races,
+but is needed to ensure that data races, as defined below, and with
+suitable restrictions on the use of atomics, correspond to data races in
+a simple interleaved (sequentially consistent) execution. — *end note*]
+The value of an atomic object M, as determined by evaluation B, is the
+value stored by some unspecified side effect A that modifies M, where B
+does not happen before A.
+[*Note 11*: The set of such side effects is also restricted by the rest
 of the rules described here, and in particular, by the coherence
 requirements below. — *end note*]
 If an operation A that modifies an atomic object M happens before an
+operation B that modifies M, then A is earlier than B in the
 modification order of M.
+[*Note 12*: This requirement is known as write-write
 coherence. — *end note*]
 If a value computation A of an atomic object M happens before a value
 computation B of M, and A takes its value from a side effect X on M,
+then the value computed by B is either the value stored by X or the
+value stored by a side effect Y on M, where Y follows X in the
 modification order of M.
+[*Note 13*: This requirement is known as read-read
 coherence. — *end note*]
 If a value computation A of an atomic object M happens before an
+operation B that modifies M, then A takes its value from a side effect X
+on M, where X precedes B in the modification order of M.
+[*Note 14*: This requirement is known as read-write
 coherence. — *end note*]
 If a side effect X on an atomic object M happens before a value
+computation B of M, then the evaluation B takes its value from X or from
+a side effect Y that follows X in the modification order of M.
+[*Note 15*: This requirement is known as write-read
 coherence. — *end note*]
+[*Note 16*: The four preceding coherence requirements effectively
 disallow compiler reordering of atomic operations to a single object,
 even if both operations are relaxed loads. This effectively makes the
 cache coherence guarantee provided by most hardware available to C++
 atomic operations. — *end note*]
+[*Note 17*: The value observed by a load of an atomic depends on the
 “happens before” relation, which depends on the values observed by loads
 of atomics. The intended reading is that there must exist an association
 of atomic loads with modifications they observe that, together with
 suitably chosen modification orders and the “happens before” relation
 derived as described above, satisfy the resulting constraints as imposed
 potentially concurrent conflicting actions, at least one of which is not
 atomic, and neither happens before the other, except for the special
 case for signal handlers described below. Any such data race results in
 undefined behavior.
+[*Note 18*: It can be shown that programs that correctly use mutexes
 and `memory_order::seq_cst` operations to prevent all data races and use
 no other synchronization operations behave as if the operations executed
 by their constituent threads were simply interleaved, with each value
 computation of an object being taken from the last side effect on that
 object in that interleaving. This is normally referred to as “sequential
 consistency”. However, this applies only to data-race-free programs, and
 data-race-free programs cannot observe most program transformations that
 do not change single-threaded program semantics. In fact, most
+single-threaded program transformations remain possible, since any
+program that behaves differently as a result has undefined
 behavior. — *end note*]
+Two accesses to the same non-bit-field object of type
+`volatile std::sig_atomic_t` do not result in a data race if both occur
+in the same thread, even if one or more occurs in a signal handler. For
+each signal handler invocation, evaluations performed by the thread
+invoking a signal handler can be divided into two groups A and B, such
+that no evaluations in B happen before evaluations in A, and the
+evaluations of such `volatile std::sig_atomic_t` objects take values as
+though all evaluations in A happened before the execution of the signal
+handler and the execution of the signal handler happened before all
+evaluations in B.
+[*Note 19*: Compiler transformations that introduce assignments to a
 potentially shared memory location that would not be modified by the
 abstract machine are generally precluded by this document, since such an
 assignment might overwrite another assignment by a different thread in
 cases in which an abstract machine execution would not have encountered
 a data race. This includes implementations of data member assignment
 that overwrite adjacent members in separate memory locations. Reordering
 of atomic loads in cases in which the atomics in question might alias is
 also generally precluded, since this could violate the coherence
 rules. — *end note*]
+[*Note 20*: It is possible that transformations that introduce a
+speculative read of a potentially shared memory location do not preserve
+the semantics of the C++ program as defined in this document, since they
+potentially introduce a data race. However, they are typically valid in
+the context of an optimizing compiler that targets a specific machine
+with well-defined semantics for data races. They would be invalid for a
 hypothetical machine that is not tolerant of races or provides hardware
 race detection. — *end note*]
 #### Forward progress <a id="intro.progress">[[intro.progress]]</a>
 The implementation may assume that any thread will eventually do one of
 the following:
 - terminate,
+- invoke the function `std::this_thread::yield` [[thread.thread.this]],
 - make a call to a library I/O function,
+- perform an access through a volatile glvalue,
+- perform an atomic or synchronization operation other than an atomic
+  modify-write operation [[atomics.order]], or
+- continue execution of a trivial infinite loop [[stmt.iter.general]].
 [*Note 1*: This is intended to allow compiler transformations such as
+removal, merging, and reordering of empty loops, even when termination
+cannot be proven. An affordance is made for trivial infinite loops,
+which cannot be removed nor reordered. — *end note*]
 Executions of atomic functions that are either defined to be lock-free
 [[atomics.flag]] or indicated as lock-free [[atomics.lockfree]] are
 *lock-free executions*.
 During the execution of a thread of execution, each of the following is
 termed an *execution step*:
 - termination of the thread of execution,
+- performing an access through a volatile glvalue,
+- completion of a call to a library I/O function, or
+- completion of an atomic or synchronization operation other than an
+  atomic modify-write operation [[atomics.order]].
 An invocation of a standard library function that blocks [[defns.block]]
 is considered to continuously execute execution steps while waiting for
 the condition that it blocks on to be satisfied.
 For a thread of execution providing *concurrent forward progress
 guarantees*, the implementation ensures that the thread will eventually
 make progress for as long as it has not terminated.
+[*Note 5*: This applies regardless of whether or not other threads of
+execution (if any) have been or are making progress. To eventually
 fulfill this requirement means that this will happen in an unspecified
 but finite amount of time. — *end note*]
 It is *implementation-defined* whether the implementation-created thread
 of execution that executes `main` [[basic.start.main]] and the threads
 arguments passed to the program from the environment in which the
 program is run. If `argc` is nonzero these arguments shall be supplied
 in `argv[0]` through `argv[argc - 1]` as pointers to the initial
 characters of null-terminated multibyte strings (NTMBSs)
 [[multibyte.strings]] and `argv[0]` shall be the pointer to the initial
+character of an NTMBS that represents the name used to invoke the
+program or `""`. The value of `argc` shall be non-negative. The value of
 `argv[argc]` shall be 0.
 *Recommended practice:* Any further (optional) parameters should be
 added after `argv`.
+The function `main` shall not be named by an expression. The linkage
 [[basic.link]] of `main` is *implementation-defined*. A program that
 defines `main` as deleted or that declares `main` to be `inline`,
 `static`, `constexpr`, or `consteval` is ill-formed. The function `main`
 shall not be a coroutine [[dcl.fct.def.coroutine]]. The `main` function
+shall not be declared with a *linkage-specification* [[dcl.link]] other
+than `"C++"`. A program that declares
 - a variable `main` that belongs to the global scope, or
 - a function `main` that belongs to the global scope and is attached to
   a named module, or
 - a function template `main` that belongs to the global scope, or
 destroy any objects with automatic storage duration [[class.dtor]]. If
 `std::exit` is invoked during the destruction of an object with static
 or thread storage duration, the program has undefined behavior.
 A `return` statement [[stmt.return]] in `main` has the effect of leaving
+the `main` function (destroying any objects with automatic storage
+duration and evaluating any postcondition assertions of `main`) and
+calling `std::exit` with the return value as the argument. If control
+flows off the end of the *compound-statement* of `main`, the effect is
+equivalent to a `return` with operand `0` (see also [[except.handle]]).
 #### Static initialization <a id="basic.start.static">[[basic.start.static]]</a>
 Variables with static storage duration are initialized as a consequence
 of program initiation. Variables with thread storage duration are
 initialized as a consequence of thread execution. Within each of these
 phases of initiation, initialization occurs as follows.
+*Constant initialization* is performed if a variable with static or
+thread storage duration is constant-initialized [[expr.const]]. If
+constant initialization is not performed, a variable with static storage
+duration [[basic.stc.static]] or thread storage duration
+[[basic.stc.thread]] is zero-initialized [[dcl.init]]. Together,
+zero-initialization and constant initialization are called
 *static initialization*; all other initialization is
 *dynamic initialization*. All static initialization strongly happens
 before [[intro.races]] any dynamic initialization.
 [*Note 1*: The dynamic initialization of non-block variables is
 It is *implementation-defined* whether the dynamic initialization of a
 non-block non-inline variable with static storage duration is sequenced
 before the first statement of `main` or is deferred. If it is deferred,
 it strongly happens before any non-initialization odr-use of any
 non-inline function or non-inline variable defined in the same
+translation unit as the variable to be initialized.[^24]
 It is *implementation-defined* in which threads and at which points in
 the program such deferred dynamic initialization occurs.
 *Recommended practice:* An implementation should choose such points in a
 Calling the function `std::abort()` declared in `<cstdlib>` terminates
 the program without executing any destructors and without calling the
 functions passed to `std::atexit()` or `std::at_quick_exit()`.

Diff to HTML by rtfpessoa