r336746 - PR38095: Allow constant-folding of loads through bitcasted pointers if

[Richard Smith via cfe-commits]

Author: rsmith
Date: Tue Jul 10 17:29:05 2018
New Revision: 336746

URL: http://llvm.org/viewvc/llvm-project?rev=336746&view=rev
Log:
PR38095: Allow constant-folding of loads through bitcasted pointers if
the bitcast only changed cvr-qualifications within the pointer type.

Modified:
    cfe/trunk/lib/AST/ExprConstant.cpp
    cfe/trunk/test/Sema/diagnose_if.c

Modified: cfe/trunk/lib/AST/ExprConstant.cpp
URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/AST/ExprConstant.cpp?rev=336746&r1=336745&r2=336746&view=diff
==============================================================================
--- cfe/trunk/lib/AST/ExprConstant.cpp (original)
+++ cfe/trunk/lib/AST/ExprConstant.cpp Tue Jul 10 17:29:05 2018
@@ -5787,8 +5787,8 @@ bool PointerExprEvaluator::VisitUnaryAdd
   return evaluateLValue(E->getSubExpr(), Result);
 }
 
-bool PointerExprEvaluator::VisitCastExpr(const CastExpr* E) {
-  const Expr* SubExpr = E->getSubExpr();
+bool PointerExprEvaluator::VisitCastExpr(const CastExpr *E) {
+  const Expr *SubExpr = E->getSubExpr();
 
   switch (E->getCastKind()) {
   default:
@@ -5805,7 +5805,11 @@ bool PointerExprEvaluator::VisitCastExpr
     // permitted in constant expressions in C++11. Bitcasts from cv void* are
     // also static_casts, but we disallow them as a resolution to DR1312.
     if (!E->getType()->isVoidPointerType()) {
-      Result.Designator.setInvalid();
+      // If we changed anything other than cvr-qualifiers, we can't use this
+      // value for constant folding. FIXME: Qualification conversions should
+      // always be CK_NoOp, but we get this wrong in C.
+      if (!Info.Ctx.hasCvrSimilarType(E->getType(), E->getSubExpr()->getType()))
+        Result.Designator.setInvalid();
       if (SubExpr->getType()->isVoidPointerType())
         CCEDiag(E, diag::note_constexpr_invalid_cast)
           << 3 << SubExpr->getType();

Modified: cfe/trunk/test/Sema/diagnose_if.c
URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/test/Sema/diagnose_if.c?rev=336746&r1=336745&r2=336746&view=diff
==============================================================================
--- cfe/trunk/test/Sema/diagnose_if.c (original)
+++ cfe/trunk/test/Sema/diagnose_if.c Tue Jul 10 17:29:05 2018
@@ -157,3 +157,13 @@ void runAlwaysWarnWithArg(int a) {
 // Bug: we would complain about `a` being undeclared if this was spelled
 // __diagnose_if__.
 void underbarName(int a) __attribute__((__diagnose_if__(a, "", "warning")));
+
+// PR38095
+void constCharStar(const char *str) __attribute__((__diagnose_if__(!str[0], "empty string not allowed", "error"))); // expected-note {{from}}
+void charStar(char *str) __attribute__((__diagnose_if__(!str[0], "empty string not allowed", "error"))); // expected-note {{from}}
+void runConstCharStar() {
+  constCharStar("foo");
+  charStar("bar");
+  constCharStar(""); // expected-error {{empty string not allowed}}
+  charStar(""); // expected-error {{empty string not allowed}}
+}