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Add a simple CG test, release note, comments for decision variable [dcl.struct.bind]
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‎clang/docs/ReleaseNotes.rst‎

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@@ -76,6 +76,8 @@ C++2c Feature Support
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- Implemented `P1061R10 Structured Bindings can introduce a Pack <https://wg21.link/P1061R10>`_.
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- Implemented `P0963R3 Structured binding declaration as a condition <https://wg21.link/P0963R3>`_.
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C++23 Feature Support
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^^^^^^^^^^^^^^^^^^^^^
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‎clang/include/clang/AST/DeclCXX.h‎

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@@ -4290,6 +4290,10 @@ class DecompositionDecl final
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std::move(Bindings));
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}
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/// The decision variable of a condition that is a structured binding
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/// declaration is specified in [dcl.struct.bind]p4:
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/// If a structured binding declaration appears as a condition, the decision
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/// variable of the condition is e.
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bool isDecisionVariable() const { return IsDecisionVariable; }
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void printName(raw_ostream &OS, const PrintingPolicy &Policy) const override;

‎clang/lib/CodeGen/CGStmt.cpp‎

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@@ -1110,6 +1110,11 @@ void CodeGenFunction::EmitWhileStmt(const WhileStmt &S,
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// execution of the loop body.
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llvm::Value *BoolCondVal = EvaluateExprAsBool(S.getCond());
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if (auto *DD =
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dyn_cast_if_present<DecompositionDecl>(S.getConditionVariable());
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DD && DD->isDecisionVariable())
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EmitDecompositionVarInit(*DD);
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// while(1) is common, avoid extra exit blocks. Be sure
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// to correctly handle break/continue though.
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llvm::ConstantInt *C = dyn_cast<llvm::ConstantInt>(BoolCondVal);
@@ -1343,6 +1348,12 @@ void CodeGenFunction::EmitForStmt(const ForStmt &S,
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// C99 6.8.5p2/p4: The first substatement is executed if the expression
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// compares unequal to 0. The condition must be a scalar type.
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llvm::Value *BoolCondVal = EvaluateExprAsBool(S.getCond());
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if (auto *DD =
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dyn_cast_if_present<DecompositionDecl>(S.getConditionVariable());
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DD && DD->isDecisionVariable())
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EmitDecompositionVarInit(*DD);
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llvm::MDNode *Weights =
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createProfileWeightsForLoop(S.getCond(), getProfileCount(S.getBody()));
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if (!Weights && CGM.getCodeGenOpts().OptimizationLevel)
@@ -2240,6 +2251,11 @@ void CodeGenFunction::EmitSwitchStmt(const SwitchStmt &S) {
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if (S.getConditionVariable())
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EmitDecl(*S.getConditionVariable());
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if (auto *DD =
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dyn_cast_if_present<DecompositionDecl>(S.getConditionVariable());
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DD && DD->isDecisionVariable())
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EmitDecompositionVarInit(*DD);
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// At this point, we are no longer "within" a switch instance, so
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// we can temporarily enforce this to ensure that any embedded case
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// statements are not emitted.
@@ -2271,6 +2287,11 @@ void CodeGenFunction::EmitSwitchStmt(const SwitchStmt &S) {
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EmitDecl(*S.getConditionVariable());
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llvm::Value *CondV = EmitScalarExpr(S.getCond());
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if (auto *DD =
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dyn_cast_if_present<DecompositionDecl>(S.getConditionVariable());
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DD && DD->isDecisionVariable())
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EmitDecompositionVarInit(*DD);
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// Create basic block to hold stuff that comes after switch
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// statement. We also need to create a default block now so that
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// explicit case ranges tests can have a place to jump to on

‎clang/lib/Sema/SemaDecl.cpp‎

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@@ -7770,7 +7770,8 @@ NamedDecl *Sema::ActOnVariableDeclarator(
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} else if (D.isDecompositionDeclarator()) {
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NewVD = DecompositionDecl::Create(
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Context, DC, D.getBeginLoc(), D.getIdentifierLoc(), R, TInfo, SC,
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Bindings, D.getContext() == DeclaratorContext::Condition);
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Bindings, /*IsDecisionVariable=*/D.getContext() ==
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DeclaratorContext::Condition);
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} else
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NewVD = VarDecl::Create(Context, DC, D.getBeginLoc(),
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D.getIdentifierLoc(), II, R, TInfo, SC);

‎clang/test/CodeGen/p0963r3.cpp‎

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@@ -0,0 +1,108 @@
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// RUN: %clang_cc1 -std=c++2c -verify -emit-llvm %s -o - | FileCheck %s
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// expected-no-diagnostics
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namespace std {
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template <typename T> struct tuple_size;
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template <int, typename> struct tuple_element;
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} // namespace std
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namespace Case1 {
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struct S {
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int a, b;
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bool called_operator_bool = false;
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operator bool() {
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called_operator_bool = true;
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return a != b;
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}
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template <int I> int get() {
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if (!called_operator_bool)
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return a + b;
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return I == 0 ? a : b;
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}
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};
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} // namespace Case1
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template <> struct std::tuple_size<Case1::S> {
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static const int value = 2;
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};
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template <int I> struct std::tuple_element<I, Case1::S> {
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using type = int;
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};
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namespace Case1 {
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void foo() {
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if (S s(1, 2); auto [a, b] = s) {
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__builtin_assume(a == 1);
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__builtin_assume(b == 2);
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}
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// CHECK: %[[call:.+]] = call {{.*}} i1 @_ZN5Case11ScvbEv
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// CHECK: %{{.*}} = call {{.*}} i32 @_ZN5Case11S3getILi0EEEiv
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// CHECK: %{{.*}} = call {{.*}} i32 @_ZN5Case11S3getILi1EEEiv
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// CHECK: br i1 %[[call]], label {{.*}}, label {{.*}}
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if (auto [a, b] = S(1, 2)) {
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__builtin_assume(a == 1);
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__builtin_assume(b == 2);
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}
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// CHECK: %[[call2:.+]] = call {{.*}} i1 @_ZN5Case11ScvbEv
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// CHECK: %{{.*}} = call {{.*}} i32 @_ZN5Case11S3getILi0EEEiv
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// CHECK: %{{.*}} = call {{.*}} i32 @_ZN5Case11S3getILi1EEEiv
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// CHECK: br i1 %[[call2]], label {{.*}}, label {{.*}}
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if (S s(3, 4); auto& [a, b] = s) {
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__builtin_assume(a == 3);
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__builtin_assume(b == 4);
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}
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// CHECK: %[[call3:.+]] = call {{.*}} i1 @_ZN5Case11ScvbEv
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// CHECK: %{{.*}} = call {{.*}} i32 @_ZN5Case11S3getILi0EEEiv
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// CHECK: %{{.*}} = call {{.*}} i32 @_ZN5Case11S3getILi1EEEiv
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// CHECK: br i1 %[[call3]], label {{.*}}, label {{.*}}
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while (auto [i, j] = S(5, 6))
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break;
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// CHECK: while.cond{{.*}}:
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// CHECK: %[[call4:.+]] = call {{.*}} i1 @_ZN5Case11ScvbEv
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// CHECK: %{{.*}} = call {{.*}} i32 @_ZN5Case11S3getILi0EEEiv
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// CHECK: %{{.*}} = call {{.*}} i32 @_ZN5Case11S3getILi1EEEiv
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// CHECK: br i1 %[[call4]], label {{.*}}, label {{.*}}
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S s(7, 8);
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while (auto& [i, j] = s)
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break;
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// CHECK: while.cond{{.*}}:
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// CHECK: %[[call5:.+]] = call {{.*}} i1 @_ZN5Case11ScvbEv
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// CHECK: %{{.*}} = call {{.*}} i32 @_ZN5Case11S3getILi0EEEiv
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// CHECK: %{{.*}} = call {{.*}} i32 @_ZN5Case11S3getILi1EEEiv
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// CHECK: br i1 %[[call5]], label {{.*}}, label {{.*}}
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for (int k = 0; auto [i, j] = S(24, 42); ++k)
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break;
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// CHECK: for.cond{{.*}}:
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// CHECK: %[[call6:.+]] = call {{.*}} i1 @_ZN5Case11ScvbEv
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// CHECK: %{{.*}} = call {{.*}} i32 @_ZN5Case11S3getILi0EEEiv
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// CHECK: %{{.*}} = call {{.*}} i32 @_ZN5Case11S3getILi1EEEiv
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// CHECK: br i1 %[[call6]], label {{.*}}, label {{.*}}
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for (S s(114, 514); auto& [i, j] = s; ++i)
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break;
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// CHECK: for.cond{{.*}}:
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// CHECK: %[[call7:.+]] = call {{.*}} i1 @_ZN5Case11ScvbEv
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// CHECK: %{{.*}} = call {{.*}} i32 @_ZN5Case11S3getILi0EEEiv
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// CHECK: %{{.*}} = call {{.*}} i32 @_ZN5Case11S3getILi1EEEiv
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// CHECK: br i1 %[[call7]], label {{.*}}, label {{.*}}
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}
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} // namespace Case1

‎clang/www/cxx_status.html‎

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@@ -223,7 +223,7 @@ <h2 id="cxx26">C++2c implementation status</h2>
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<tr>
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<td>Structured binding declaration as a condition</td>
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<td><a href="https://wg21.link/P0963R3">P0963R3</a></td>
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<td class="none" align="center">No</td>
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<td class="unreleased" align="center">Clang 21</td>
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</tr>
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<!--Poland, Fall 2024-->
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<tr>

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