Author: rakete1111 Date: Thu Jan 10 11:03:33 2019 New Revision: 350874 URL: http://llvm.org/viewvc/llvm-project?rev=350874&view=rev Log: Fix false positive unsequenced access and modification warning in array subscript expression.
Summary: In the [expr.sub] p1, we can read that for a given E1[E2], E1 is sequenced before E2. Patch by Mateusz Janek. Reviewers: rsmith, Rakete1111 Reviewed By: rsmith, Rakete1111 Subscribers: riccibruno, lebedev.ri, Rakete1111, hiraditya, cfe-commits Tags: #clang Differential Revision: https://reviews.llvm.org/D50766 Added: cfe/trunk/test/SemaCXX/warn-unsequenced-cxx17.cpp Modified: cfe/trunk/lib/Sema/SemaChecking.cpp cfe/trunk/test/SemaCXX/warn-unsequenced.cpp Modified: cfe/trunk/lib/Sema/SemaChecking.cpp URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/Sema/SemaChecking.cpp?rev=350874&r1=350873&r2=350874&view=diff ============================================================================== --- cfe/trunk/lib/Sema/SemaChecking.cpp (original) +++ cfe/trunk/lib/Sema/SemaChecking.cpp Thu Jan 10 11:03:33 2019 @@ -11908,30 +11908,42 @@ public: notePostUse(O, E); } - void VisitBinComma(BinaryOperator *BO) { - // C++11 [expr.comma]p1: - // Every value computation and side effect associated with the left - // expression is sequenced before every value computation and side - // effect associated with the right expression. - SequenceTree::Seq LHS = Tree.allocate(Region); - SequenceTree::Seq RHS = Tree.allocate(Region); + void VisitSequencedExpressions(Expr *SequencedBefore, Expr *SequencedAfter) { + SequenceTree::Seq BeforeRegion = Tree.allocate(Region); + SequenceTree::Seq AfterRegion = Tree.allocate(Region); SequenceTree::Seq OldRegion = Region; { - SequencedSubexpression SeqLHS(*this); - Region = LHS; - Visit(BO->getLHS()); + SequencedSubexpression SeqBefore(*this); + Region = BeforeRegion; + Visit(SequencedBefore); } - Region = RHS; - Visit(BO->getRHS()); + Region = AfterRegion; + Visit(SequencedAfter); Region = OldRegion; - // Forget that LHS and RHS are sequenced. They are both unsequenced - // with respect to other stuff. - Tree.merge(LHS); - Tree.merge(RHS); + Tree.merge(BeforeRegion); + Tree.merge(AfterRegion); + } + + void VisitArraySubscriptExpr(ArraySubscriptExpr *ASE) { + // C++17 [expr.sub]p1: + // The expression E1[E2] is identical (by definition) to *((E1)+(E2)). The + // expression E1 is sequenced before the expression E2. + if (SemaRef.getLangOpts().CPlusPlus17) + VisitSequencedExpressions(ASE->getLHS(), ASE->getRHS()); + else + Base::VisitStmt(ASE); + } + + void VisitBinComma(BinaryOperator *BO) { + // C++11 [expr.comma]p1: + // Every value computation and side effect associated with the left + // expression is sequenced before every value computation and side + // effect associated with the right expression. + VisitSequencedExpressions(BO->getLHS(), BO->getRHS()); } void VisitBinAssign(BinaryOperator *BO) { Added: cfe/trunk/test/SemaCXX/warn-unsequenced-cxx17.cpp URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/test/SemaCXX/warn-unsequenced-cxx17.cpp?rev=350874&view=auto ============================================================================== --- cfe/trunk/test/SemaCXX/warn-unsequenced-cxx17.cpp (added) +++ cfe/trunk/test/SemaCXX/warn-unsequenced-cxx17.cpp Thu Jan 10 11:03:33 2019 @@ -0,0 +1,8 @@ +// RUN: %clang_cc1 -fsyntax-only -verify -std=c++17 -Wno-unused %s + +void test() { + int xs[10]; + int *p = xs; + // expected-no-diagnostics + p[(long long unsigned)(p = 0)]; // ok +} Modified: cfe/trunk/test/SemaCXX/warn-unsequenced.cpp URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/test/SemaCXX/warn-unsequenced.cpp?rev=350874&r1=350873&r2=350874&view=diff ============================================================================== --- cfe/trunk/test/SemaCXX/warn-unsequenced.cpp (original) +++ cfe/trunk/test/SemaCXX/warn-unsequenced.cpp Thu Jan 10 11:03:33 2019 @@ -81,6 +81,7 @@ void test() { int *p = xs; a = *(a++, p); // ok a = a++ && a; // ok + p[(long long unsigned)(p = 0)]; // expected-warning {{unsequenced modification and access to 'p'}} A *q = &agg1; (q = &agg2)->y = q->x; // expected-warning {{unsequenced modification and access to 'q'}} _______________________________________________ cfe-commits mailing list cfe-commits@lists.llvm.org http://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
