[PATCH] D52918: Emit CK_NoOp casts in C mode, not just C++.

[James Y Knight via Phabricator via cfe-commits]

jyknight created this revision.
jyknight added a reviewer: rsmith.

Previously, it had been using CK_BitCast even for casts that only
change const/restrict/volatile. Now it will use CK_Noop where
appropriate.

This is an alternate solution to r336746.


https://reviews.llvm.org/D52918

Files:
  clang/lib/AST/ExprConstant.cpp
  clang/lib/Sema/SemaExpr.cpp


Index: clang/lib/Sema/SemaExpr.cpp
===================================================================
--- clang/lib/Sema/SemaExpr.cpp
+++ clang/lib/Sema/SemaExpr.cpp
@@ -5846,7 +5846,9 @@
   // pointers.  Everything else should be possible.
 
   QualType SrcTy = Src.get()->getType();
-  if (Context.hasSameUnqualifiedType(SrcTy, DestTy))
+  // We can use a no-op cast if the types are the same, or only adding/removing
+  // const, volatile, or restricted qualifiers.
+  if (Context.hasCvrSimilarType(SrcTy, DestTy))
     return CK_NoOp;
 
   switch (Type::ScalarTypeKind SrcKind = SrcTy->getScalarTypeKind()) {
@@ -7762,7 +7764,12 @@
     if (isa<PointerType>(RHSType)) {
       LangAS AddrSpaceL = LHSPointer->getPointeeType().getAddressSpace();
       LangAS AddrSpaceR = RHSType->getPointeeType().getAddressSpace();
-      Kind = AddrSpaceL != AddrSpaceR ? CK_AddressSpaceConversion : CK_BitCast;
+      if (AddrSpaceL != AddrSpaceR)
+        Kind = CK_AddressSpaceConversion;
+      else if (Context.hasCvrSimilarType(RHSType, LHSType))
+        Kind = CK_NoOp;
+      else
+        Kind = CK_BitCast;
       return checkPointerTypesForAssignment(*this, LHSType, RHSType);
     }
 
Index: clang/lib/AST/ExprConstant.cpp
===================================================================
--- clang/lib/AST/ExprConstant.cpp
+++ clang/lib/AST/ExprConstant.cpp
@@ -5861,11 +5861,7 @@
     // 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()) {
-      // 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();
+      Result.Designator.setInvalid();
       if (SubExpr->getType()->isVoidPointerType())
         CCEDiag(E, diag::note_constexpr_invalid_cast)
           << 3 << SubExpr->getType();


-------------- next part --------------
A non-text attachment was scrubbed...
Name: D52918.168415.patch
Type: text/x-patch
Size: 2110 bytes
Desc: not available
URL: <http://lists.llvm.org/pipermail/cfe-commits/attachments/20181005/8e101dc6/attachment.bin>