[OpenMP] diagnose assign to firstprivate const

[jdenny]

Summary

[OpenMP] diagnose assign to firstprivate const

Clang does not diagnose assignments to const variables declared
firstprivate. Furthermore, codegen is broken such that, at run time,
such assignments simply have no effect. For example, the following
prints 0 not 1:

int main() {

const int i = 0;
#pragma omp parallel firstprivate(i)
{ i=1; printf("%d\n", i); }
return 0;

}

This commit makes these assignments a compile error, which is
consistent with other OpenMP compilers I've tried (pgcc 17.4-0, gcc
6.3.0).

[ABataev]

lib/Sema/SemaExpr.cpp

14356

hasConst must start from capital letter HasConst.

14360

Better to make it this way:

DeclRefType.addConst();

test/OpenMP/parallel_firstprivate_messages.cpp

75

Please, add a separate directive with this assignment

[jdenny]

Hi Alexey. Thanks for your comments. This update should address them all.

[ABataev]

LG

[jdenny]

Alexey: Thanks for accepting. I do not have commit privileges. Would you please commit for me?

[ABataev]

In D39859#921780, @jdenny wrote:

Alexey: Thanks for accepting. I do not have commit privileges. Would you please commit for me?

Sure, no problems.

lib/Sema/SemaExpr.cpp

static bool captureInCapturedRegion(CapturedRegionScopeInfo *RSI,
                                     QualType &CaptureType,
                                     QualType &DeclRefType, 
                                     const bool RefersToCapturedVariable,
                                     Sema &S) {
   // By default, capture variables by reference.
   bool ByRef = true;
   // Using an LValue reference type is consistent with Lambdas (see below).
   if (S.getLangOpts().OpenMP && RSI->CapRegionKind == CR_OpenMP) {
-    if (S.IsOpenMPCapturedDecl(Var))
+    if (S.IsOpenMPCapturedDecl(Var)) {
+      bool HasConst = DeclRefType.isConstQualified();
       DeclRefType = DeclRefType.getUnqualifiedType();
+      // Don't lose diagnostics about assignments to const.
+      if (HasConst)
+        DeclRefType.addConst();
+    }
     ByRef = S.IsOpenMPCapturedByRef(Var, RSI->OpenMPLevel);
   }
 
   if (ByRef)
     CaptureType = S.Context.getLValueReferenceType(DeclRefType);
   else
     CaptureType = DeclRefType;
 

test/OpenMP/parallel_firstprivate_messages.cpp

 double x;
 #pragma omp threadprivate(x) // expected-note {{defined as threadprivate or thread local}}
 }
 namespace B {
 using A::x;
 }
 
 int main(int argc, char **argv) {
-  const int d = 5;
+  const int d = 5; // expected-note {{variable 'd' declared const here}}
   const int da[5] = { 0 };
   S4 e(4);
   S5 g(5);
   int i;
   int &j = i;
   static int m;
   #pragma omp parallel firstprivate // expected-error {{expected '(' after 'firstprivate'}}
   #pragma omp parallel firstprivate ( // expected-error {{expected expression}} expected-error {{expected ')'}} expected-note {{to match this '('}}
   #pragma omp parallel firstprivate () // expected-error {{expected expression}}
   #pragma omp parallel firstprivate (argc // expected-error {{expected ')'}} expected-note {{to match this '('}}
   #pragma omp parallel firstprivate (argc, // expected-error {{expected expression}} expected-error {{expected ')'}} expected-note {{to match this '('}}
   #pragma omp parallel firstprivate (argc > 0 ? argv[1] : argv[2]) // expected-error {{expected variable name}}
   #pragma omp parallel firstprivate (argc)
   #pragma omp parallel firstprivate (S1) // expected-error {{'S1' does not refer to a value}}
   #pragma omp parallel firstprivate (a, b, c, d, f) // expected-error {{firstprivate variable with incomplete type 'S1'}}
+  #pragma omp parallel firstprivate (d)
+    d = 5; // expected-error {{cannot assign to variable 'd' with const-qualified type}}
   #pragma omp parallel firstprivate (argv[1]) // expected-error {{expected variable name}}
   #pragma omp parallel firstprivate(ba)
   #pragma omp parallel firstprivate(ca)
   #pragma omp parallel firstprivate(da)
   #pragma omp parallel firstprivate(S2::S2s)
   #pragma omp parallel firstprivate(S2::S2sc)
   #pragma omp parallel firstprivate(e, g) // expected-error {{calling a private constructor of class 'S4'}} expected-error {{calling a private constructor of class 'S5'}}
   #pragma omp parallel firstprivate(h, B::x) // expected-error 2 {{threadprivate or thread local variable cannot be firstprivate}}