[CodeGen] Refactor TLI/AtomicExpand interface to make LLSC explicit.

We used to have this magic "hasLoadLinkedStoreConditional()" callback,
which really meant two things:
- expand cmpxchg (to ll/sc).
- expand atomic loads using ll/sc (rather than cmpxchg).

Remove it, and, instead, introduce explicit callbacks:
- bool shouldExpandAtomicCmpXchgInIR(inst)
- AtomicExpansionKind shouldExpandAtomicLoadInIR(inst)

Differential Revision: http://reviews.llvm.org/D12557

llvm-svn: 247429

1 files changed, 5 insertions, 3 deletions

diff --git a/llvm/lib/Target/X86/X86ISelLowering.cpp b/llvm/lib/Target/X86/X86ISelLowering.cpp
index 611ccb92e4f..c338a4db23a 100644
--- a/llvm/lib/Target/X86/X86ISelLowering.cpp
+++ b/llvm/lib/Target/X86/X86ISelLowering.cpp
@@ -18406,12 +18406,14 @@ bool X86TargetLowering::shouldExpandAtomicStoreInIR(StoreInst *SI) const {
 
 // Note: this turns large loads into lock cmpxchg8b/16b.
 // FIXME: On 32 bits x86, fild/movq might be faster than lock cmpxchg8b.
-bool X86TargetLowering::shouldExpandAtomicLoadInIR(LoadInst *LI) const {
+TargetLowering::AtomicExpansionKind
+X86TargetLowering::shouldExpandAtomicLoadInIR(LoadInst *LI) const {
   auto PTy = cast<PointerType>(LI->getPointerOperand()->getType());
-  return needsCmpXchgNb(PTy->getElementType());
+  return needsCmpXchgNb(PTy->getElementType()) ? AtomicExpansionKind::CmpXChg
+                                               : AtomicExpansionKind::None;
 }
 
-TargetLoweringBase::AtomicExpansionKind
+TargetLowering::AtomicExpansionKind
 X86TargetLowering::shouldExpandAtomicRMWInIR(AtomicRMWInst *AI) const {
   unsigned NativeWidth = Subtarget->is64Bit() ? 64 : 32;
   Type *MemType = AI->getType();