[LoopStrengthReduce, x86] don't add cost for a cmp that will be macro-fused (PR35681)

In the motivating case from PR35681 and represented by the macro-fuse-cmp test:
https://bugs.llvm.org/show_bug.cgi?id=35681
...there's a 37 -> 31 byte size win for the loop because we eliminate the big base 
address offsets.

SPEC2017 on Ryzen shows no significant perf difference.

Differential Revision: https://reviews.llvm.org/D42607

llvm-svn: 324289

2 files changed, 5 insertions, 0 deletions

diff --git a/llvm/lib/Target/X86/X86TargetTransformInfo.cpp b/llvm/lib/Target/X86/X86TargetTransformInfo.cpp
index 8571be8cd2b..adda3490819 100644
--- a/llvm/lib/Target/X86/X86TargetTransformInfo.cpp
+++ b/llvm/lib/Target/X86/X86TargetTransformInfo.cpp
@@ -2482,6 +2482,10 @@ bool X86TTIImpl::isLSRCostLess(TargetTransformInfo::LSRCost &C1,
                     C2.ScaleCost, C2.ImmCost, C2.SetupCost);
 }
 
+bool X86TTIImpl::canMacroFuseCmp() {
+  return ST->hasMacroFusion();
+}
+
 bool X86TTIImpl::isLegalMaskedLoad(Type *DataTy) {
   // The backend can't handle a single element vector.
   if (isa<VectorType>(DataTy) && DataTy->getVectorNumElements() == 1)
diff --git a/llvm/lib/Target/X86/X86TargetTransformInfo.h b/llvm/lib/Target/X86/X86TargetTransformInfo.h
index 6f01a6fd11d..3df89903882 100644
--- a/llvm/lib/Target/X86/X86TargetTransformInfo.h
+++ b/llvm/lib/Target/X86/X86TargetTransformInfo.h
@@ -120,6 +120,7 @@ public:
                     Type *Ty);
   bool isLSRCostLess(TargetTransformInfo::LSRCost &C1,
                      TargetTransformInfo::LSRCost &C2);
+  bool canMacroFuseCmp();
   bool isLegalMaskedLoad(Type *DataType);
   bool isLegalMaskedStore(Type *DataType);
   bool isLegalMaskedGather(Type *DataType);