First pass at implementing C++ enum semantics: calculate (and store) an

"integer promotion" type associated with an enum decl, and use this type to
determine which type to promote to.  This type obeys C++ [conv.prom]p2 and
is therefore generally signed unless the range of the enumerators forces
it to be unsigned.

Kills off a lot of false positives from -Wsign-compare in C++, addressing
rdar://7455616

llvm-svn: 90965

1 files changed, 11 insertions, 9 deletions

diff --git a/clang/lib/Sema/SemaOverload.cpp b/clang/lib/Sema/SemaOverload.cpp
index 2555f5bde60..4443de05380 100644
--- a/clang/lib/Sema/SemaOverload.cpp
+++ b/clang/lib/Sema/SemaOverload.cpp
@@ -754,19 +754,21 @@ bool Sema::IsIntegralPromotion(Expr *From, QualType FromType, QualType ToType) {
   // can be converted to an rvalue of the first of the following types
   // that can represent all the values of its underlying type: int,
   // unsigned int, long, or unsigned long (C++ 4.5p2).
-  if ((FromType->isEnumeralType() || FromType->isWideCharType())
-      && ToType->isIntegerType()) {
+
+  // We pre-calculate the promotion type for enum types.
+  if (const EnumType *FromEnumType = FromType->getAs<EnumType>())
+    if (ToType->isIntegerType())
+      return Context.hasSameUnqualifiedType(ToType,
+                                FromEnumType->getDecl()->getPromotionType());
+
+  if (FromType->isWideCharType() && ToType->isIntegerType()) {
     // Determine whether the type we're converting from is signed or
     // unsigned.
     bool FromIsSigned;
     uint64_t FromSize = Context.getTypeSize(FromType);
-    if (const EnumType *FromEnumType = FromType->getAs<EnumType>()) {
-      QualType UnderlyingType = FromEnumType->getDecl()->getIntegerType();
-      FromIsSigned = UnderlyingType->isSignedIntegerType();
-    } else {
-      // FIXME: Is wchar_t signed or unsigned? We assume it's signed for now.
-      FromIsSigned = true;
-    }
+    
+    // FIXME: Is wchar_t signed or unsigned? We assume it's signed for now.
+    FromIsSigned = true;
 
     // The types we'll try to promote to, in the appropriate
     // order. Try each of these types.