Add warning when assigning enums to bitfields without an explicit unsigned underlying type
Summary:
Add a warning when assigning enums to bitfields without an explicit
unsigned underlying type. This is to prevent problems with MSVC
compatibility, since the Microsoft ABI defaults to storing enums with a
signed type, causing inconsistencies with saving to/reading from
bitfields.
Also disabled the warning in the dr0xx.cpp test which throws the error,
and added a test for the warning.
The warning can be disabled with -Wno-signed-enum-bitfield.
Patch by Sasha Bermeister!
Reviewers: rnk, aaron.ballman
Subscribers: mehdi_amini, aaron.ballman, cfe-commits, thakis, dcheng
Differential Revision: https://reviews.llvm.org/D24289
llvm-svn: 287177
diff --git a/clang/lib/Sema/SemaChecking.cpp b/clang/lib/Sema/SemaChecking.cpp
index 56bc3ac..c1db062 100644
--- a/clang/lib/Sema/SemaChecking.cpp
+++ b/clang/lib/Sema/SemaChecking.cpp
@@ -8518,6 +8518,24 @@
return false;
// White-list bool bitfields.
+ QualType BitfieldType = Bitfield->getType();
+ if (BitfieldType->isBooleanType())
+ return false;
+
+ if (BitfieldType->isEnumeralType()) {
+ EnumDecl *BitfieldEnumDecl = BitfieldType->getAs<EnumType>()->getDecl();
+ // If the underlying enum type was not explicitly specified as an unsigned
+ // type and the enum contain only positive values, MSVC++ will cause an
+ // inconsistency by storing this as a signed type.
+ if (S.getLangOpts().CPlusPlus11 &&
+ !BitfieldEnumDecl->getIntegerTypeSourceInfo() &&
+ BitfieldEnumDecl->getNumPositiveBits() > 0 &&
+ BitfieldEnumDecl->getNumNegativeBits() == 0) {
+ S.Diag(InitLoc, diag::warn_no_underlying_type_specified_for_enum_bitfield)
+ << BitfieldEnumDecl->getNameAsString();
+ }
+ }
+
if (Bitfield->getType()->isBooleanType())
return false;
@@ -8547,7 +8565,7 @@
// Compute the value which the bitfield will contain.
llvm::APSInt TruncatedValue = Value.trunc(FieldWidth);
- TruncatedValue.setIsSigned(Bitfield->getType()->isSignedIntegerType());
+ TruncatedValue.setIsSigned(BitfieldType->isSignedIntegerType());
// Check whether the stored value is equal to the original value.
TruncatedValue = TruncatedValue.extend(OriginalWidth);