[OpenACC] Implement Duffs-Device restriction for Compute Constructs (llvm#83460)

Like the last few patches, branching in/out of a compute construct is
not valid. This patch implements checking to ensure that a 'case' or
'default' statement cannot jump into a Compute Construct (in the style
of a duff's device!).

Author: erichkeane

clang/include/clang/Sema/Scope.h

@@ -534,6 +534,25 @@ class Scope {
     return false;
   }
 
+  /// Determine if this scope (or its parents) are a compute construct inside of
+  /// the nearest 'switch' scope.  This is needed to check whether we are inside
+  /// of a 'duffs' device, which is an illegal branch into a compute construct.
+  bool isInOpenACCComputeConstructBeforeSwitch() const {
+    for (const Scope *S = this; S; S = S->getParent()) {
+      if (S->getFlags() & Scope::OpenACCComputeConstructScope)
+        return true;
+      if (S->getFlags() & Scope::SwitchScope)
+        return false;
+
+      if (S->getFlags() &
+          (Scope::FnScope | Scope::ClassScope | Scope::BlockScope |
+           Scope::TemplateParamScope | Scope::FunctionPrototypeScope |
+           Scope::AtCatchScope | Scope::ObjCMethodScope))
+        return false;
+    }
+    return false;
+  }
+
   /// Determine whether this scope is a while/do/for statement, which can have
   /// continue statements embedded into it.
   bool isContinueScope() const {

clang/lib/Sema/SemaStmt.cpp

@@ -527,6 +527,13 @@ Sema::ActOnCaseStmt(SourceLocation CaseLoc, ExprResult LHSVal,
     return StmtError();
   }
 
+  if (LangOpts.OpenACC &&
+      getCurScope()->isInOpenACCComputeConstructBeforeSwitch()) {
+    Diag(CaseLoc, diag::err_acc_branch_in_out_compute_construct)
+        << /*branch*/ 0 << /*into*/ 1;
+    return StmtError();
+  }
+
   auto *CS = CaseStmt::Create(Context, LHSVal.get(), RHSVal.get(),
                               CaseLoc, DotDotDotLoc, ColonLoc);
   getCurFunction()->SwitchStack.back().getPointer()->addSwitchCase(CS);
@@ -546,6 +553,13 @@ Sema::ActOnDefaultStmt(SourceLocation DefaultLoc, SourceLocation ColonLoc,
     return SubStmt;
   }
 
+  if (LangOpts.OpenACC &&
+      getCurScope()->isInOpenACCComputeConstructBeforeSwitch()) {
+    Diag(DefaultLoc, diag::err_acc_branch_in_out_compute_construct)
+        << /*branch*/ 0 << /*into*/ 1;
+    return StmtError();
+  }
+
   DefaultStmt *DS = new (Context) DefaultStmt(DefaultLoc, ColonLoc, SubStmt);
   getCurFunction()->SwitchStack.back().getPointer()->addSwitchCase(DS);
   return DS;

clang/test/SemaOpenACC/no-branch-in-out.c

@@ -310,3 +310,30 @@ LABEL4:{}
 
   ptr=&&LABEL5;
 }
+
+void DuffsDevice() {
+  int j;
+  switch (j) {
+#pragma acc parallel
+  for(int i =0; i < 5; ++i) {
+    case 0: // expected-error{{invalid branch into OpenACC Compute Construct}}
+      {}
+  }
+  }
+
+  switch (j) {
+#pragma acc parallel
+  for(int i =0; i < 5; ++i) {
+    default: // expected-error{{invalid branch into OpenACC Compute Construct}}
+      {}
+  }
+  }
+
+  switch (j) {
+#pragma acc parallel
+  for(int i =0; i < 5; ++i) {
+    case 'a' ... 'z': // expected-error{{invalid branch into OpenACC Compute Construct}}
+      {}
+  }
+  }
+}

clang/test/SemaOpenACC/no-branch-in-out.cpp

@@ -18,7 +18,6 @@ void ReturnTest() {
 
 template<typename T>
 void BreakContinue() {
-
 #pragma acc parallel
   for(int i =0; i < 5; ++i) {
     switch(i) {
@@ -109,6 +108,35 @@ void BreakContinue() {
   } while (j );
 }
 
+template<typename T>
+void DuffsDevice() {
+  int j;
+  switch (j) {
+#pragma acc parallel
+  for(int i =0; i < 5; ++i) {
+    case 0: // expected-error{{invalid branch into OpenACC Compute Construct}}
+      {}
+  }
+  }
+
+  switch (j) {
+#pragma acc parallel
+  for(int i =0; i < 5; ++i) {
+    default: // expected-error{{invalid branch into OpenACC Compute Construct}}
+      {}
+  }
+  }
+
+  switch (j) {
+#pragma acc parallel
+  for(int i =0; i < 5; ++i) {
+    case 'a' ... 'z': // expected-error{{invalid branch into OpenACC Compute Construct}}
+      {}
+  }
+  }
+}
+
 void Instantiate() {
   BreakContinue<int>();
+  DuffsDevice<int>();
 }