[OpenACC] Properly ignore side-effects in clause arguments

The OpenACC standard makes depending on side effects to be effectively
UB, so this patch ensures we handle them reaonably by making it a potentially
evaluated context, and ignoring cleanups.

Author: erichkeane

clang/lib/Sema/SemaOpenACC.cpp

@@ -1210,6 +1210,10 @@ ExprResult SemaOpenACC::CheckReductionVar(Expr *VarExpr) {
 
 void SemaOpenACC::ActOnConstruct(OpenACCDirectiveKind K,
                                  SourceLocation DirLoc) {
+  // Start an evaluation context to parse the clause arguments on.
+  SemaRef.PushExpressionEvaluationContext(
+      Sema::ExpressionEvaluationContext::PotentiallyEvaluated);
+
   switch (K) {
   case OpenACCDirectiveKind::Invalid:
     // Nothing to do here, an invalid kind has nothing we can check here.  We
@@ -1626,6 +1630,8 @@ ExprResult SemaOpenACC::ActOnArraySectionExpr(Expr *Base, SourceLocation LBLoc,
 
 bool SemaOpenACC::ActOnStartStmtDirective(OpenACCDirectiveKind K,
                                           SourceLocation StartLoc) {
+  SemaRef.DiscardCleanupsInEvaluationContext();
+  SemaRef.PopExpressionEvaluationContext();
   return diagnoseConstructAppertainment(*this, K, StartLoc, /*IsStmt=*/true);
 }
 
@@ -1649,6 +1655,7 @@ StmtResult SemaOpenACC::ActOnEndStmtDirective(OpenACCDirectiveKind K,
         ParentlessLoopConstructs);
 
     ParentlessLoopConstructs.clear();
+
     return ComputeConstruct;
   }
   case OpenACCDirectiveKind::Loop: {
@@ -1704,6 +1711,11 @@ StmtResult SemaOpenACC::ActOnAssociatedStmt(SourceLocation DirectiveLoc,
 
 bool SemaOpenACC::ActOnStartDeclDirective(OpenACCDirectiveKind K,
                                           SourceLocation StartLoc) {
+  // OpenCC3.3 2.1 (line 889)
+  // A program must not depend on the order of evaluation of expressions in
+  // clause arguments or on any side effects of the evaluations.
+  SemaRef.DiscardCleanupsInEvaluationContext();
+  SemaRef.PopExpressionEvaluationContext();
   return diagnoseConstructAppertainment(*this, K, StartLoc, /*IsStmt=*/false);
 }
 

clang/test/SemaOpenACC/compute-construct-ast.cpp

@@ -117,5 +117,26 @@ struct S {
 void use() {
   TemplFunc<S>();
 }
-#endif
 
+struct HasCtor { HasCtor(); operator int(); ~HasCtor();};
+
+void useCtorType() {
+  // CHECK-LABEL: useCtorType
+  // CHECK-NEXT: CompoundStmt
+
+#pragma acc kernels num_workers(HasCtor{})
+  // CHECK-NEXT: OpenACCComputeConstruct{{.*}} kernels
+  // CHECK-NEXT: num_workers clause
+  // CHECK-NEXT: ImplicitCastExpr{{.*}}'int' <UserDefinedConversion>
+  // CHECK-NEXT: CXXMemberCallExpr{{.*}}'int'
+  // CHECK-NEXT: MemberExpr{{.*}}.operator int
+  // CHECK-NEXT: MaterializeTemporaryExpr{{.*}}'HasCtor'
+  // CHECK-NEXT: CXXBindTemporaryExpr{{.*}}'HasCtor'
+  // CHECK-NEXT: CXXTemporaryObjectExpr{{.*}}'HasCtor'
+
+  while(true);
+  // CHECK-NEXT: WhileStmt
+  // CHECK-NEXT: CXXBoolLiteralExpr
+  // CHECK-NEXT: NullStmt
+}
+#endif