Fix assertion failure with constant lvalues.

[johngarvin]

Summary

(Resubmitted with Phabricator for easier reviewing.)

This fixes an assertion failure in assignment if an lvalue is constant but its
type is not const-qualified.

An expression may be MLV_ConstQualified either because the type is actually
“const” or because it’s in the OpenCL constant address space (see
ExprClassification.cpp:608). Unfortunately, isReferenceToConstCapture asserts
that the type must actually be “const”, which is not necessarily true. This
patch changes the assertion to what I think is intended.

[rsmith]

It seems to me that the bug is using MLV_ConstQualified to represent a situation other than a const qualifier. A better fix would be to add a separate enumeration value for this case.

[johngarvin]

Add new enumeration value for variables in constant address space.

[rsmith]

LGTM

It'd be nice to give a more specific diagnostic for this change, but let's get the assert fix in for now. Do you have commit access?

[johngarvin]

No, no commit access.

John

[johngarvin]

Ping. Is this ready to commit?

John

[rsmith]

Committed as r237983.

lib/Sema/SemaExpr.cpp

static bool IsReadonlyMessage(Expr *E, Sema &S) {
   return Base->getMethodDecl() != nullptr;
 }
 
 /// Is the given expression (which must be 'const') a reference to a
 /// variable which was originally non-const, but which has become
 /// 'const' due to being captured within a block?
 enum NonConstCaptureKind { NCCK_None, NCCK_Block, NCCK_Lambda };
 static NonConstCaptureKind isReferenceToNonConstCapture(Sema &S, Expr *E) {
-  assert(E->isLValue() && E->getType().isConstQualified());
+  assert(E->isModifiableLvalue(S.getASTContext()) == Expr::MLV_ConstQualified);
   E = E->IgnoreParens();
 
   // Must be a reference to a declaration from an enclosing scope.
   DeclRefExpr *DRE = dyn_cast<DeclRefExpr>(E);
   if (!DRE) return NCCK_None;
   if (!DRE->refersToEnclosingVariableOrCapture()) return NCCK_None;
 
   // The declaration must be a variable which is not declared 'const'.

test/Sema/invalid-assignment-constant-address-space.c

+// RUN: %clang_cc1 %s -verify -pedantic -fsyntax-only
+
+#define OPENCL_CONSTANT 16776962
+int __attribute__((address_space(OPENCL_CONSTANT))) c[3] = {0};
+
+void foo() {
+  c[0] = 1; //expected-error{{read-only variable is not assignable}}
+}