after going around in circles a few times, finally cave and emit structure
copies with memcpy instead of memmove. This matches what GCC does and if it
causes a problem with a particular libc we can always fix it with a target
hook.
git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@65699 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/CodeGen/CGExprAgg.cpp b/lib/CodeGen/CGExprAgg.cpp
index e2f5c79..b0596e2 100644
--- a/lib/CodeGen/CGExprAgg.cpp
+++ b/lib/CodeGen/CGExprAgg.cpp
@@ -518,7 +518,16 @@
llvm::Value *SrcPtr, QualType Ty) {
assert(!Ty->isAnyComplexType() && "Shouldn't happen for complex");
- // Aggregate assignment turns into llvm.memmove.
+ // Aggregate assignment turns into llvm.memset. This is almost valid per
+ // C99 6.5.16.1p3, which states "If the value being stored in an object is
+ // read from another object that overlaps in anyway the storage of the first
+ // object, then the overlap shall be exact and the two objects shall have
+ // qualified or unqualified versions of a compatible type."
+ //
+ // memset is not defined if the source and destination pointers are exactly
+ // equal, but other compilers do this optimization, and almost every memcpy
+ // implementation handles this case safely. If there is a libc that does not
+ // safely handle this, we can add a target hook.
const llvm::Type *BP = llvm::PointerType::getUnqual(llvm::Type::Int8Ty);
if (DestPtr->getType() != BP)
DestPtr = Builder.CreateBitCast(DestPtr, BP, "tmp");
@@ -531,7 +540,7 @@
// FIXME: Handle variable sized types.
const llvm::Type *IntPtr = llvm::IntegerType::get(LLVMPointerWidth);
- Builder.CreateCall4(CGM.getMemMoveFn(),
+ Builder.CreateCall4(CGM.getMemCpyFn(),
DestPtr, SrcPtr,
// TypeInfo.first describes size in bits.
llvm::ConstantInt::get(IntPtr, TypeInfo.first/8),