[MSVC Compat] Don't provide /volatile:ms semantics to types > pointer
Volatile loads of type wider than a pointer get split by MSVC because
the base x86 ISA doesn't provide loads which are wider than pointer
width. LLVM assumes that it can emit an cmpxchg8b but this is
problematic if the memory is in a CONST memory segment.
Instead, provide behavior compatible with MSVC: split loads wider than a
pointer.
llvm-svn: 258506
diff --git a/clang/lib/CodeGen/CGAtomic.cpp b/clang/lib/CodeGen/CGAtomic.cpp
index 1ef5d10..4e52c36 100644
--- a/clang/lib/CodeGen/CGAtomic.cpp
+++ b/clang/lib/CodeGen/CGAtomic.cpp
@@ -1295,10 +1295,23 @@
/// performing such an operation can be performed without a libcall.
bool CodeGenFunction::typeIsSuitableForInlineAtomic(QualType Ty,
bool IsVolatile) const {
+ // The operation must be volatile for us to make it atomic.
+ if (!IsVolatile)
+ return false;
+ // The -fms-volatile flag must be passed for us to adopt this behavior.
+ if (!CGM.getCodeGenOpts().MSVolatile)
+ return false;
+
// An atomic is inline if we don't need to use a libcall (e.g. it is builtin).
- bool AtomicIsInline = getContext().getTargetInfo().hasBuiltinAtomic(
- getContext().getTypeSize(Ty), getContext().getTypeAlign(Ty));
- return CGM.getCodeGenOpts().MSVolatile && IsVolatile && AtomicIsInline;
+ if (!getContext().getTargetInfo().hasBuiltinAtomic(
+ getContext().getTypeSize(Ty), getContext().getTypeAlign(Ty)))
+ return false;
+
+ // MSVC doesn't seem to do this for types wider than a pointer.
+ if (getContext().getTypeSize(Ty) >
+ getContext().getTypeSize(getContext().getIntPtrType()))
+ return false;
+ return true;
}
RValue CodeGenFunction::EmitAtomicLoad(LValue LV, SourceLocation SL,