[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
diff --git a/llvm/lib/Transforms/Scalar/LoopStrengthReduce.cpp b/llvm/lib/Transforms/Scalar/LoopStrengthReduce.cpp
index 4b8e228..b7d9a25 100644
--- a/llvm/lib/Transforms/Scalar/LoopStrengthReduce.cpp
+++ b/llvm/lib/Transforms/Scalar/LoopStrengthReduce.cpp
@@ -1343,14 +1343,15 @@
// If ICmpZero formula ends with not 0, it could not be replaced by
// just add or sub. We'll need to compare final result of AddRec.
- // That means we'll need an additional instruction.
+ // That means we'll need an additional instruction. But if the target can
+ // macro-fuse a compare with a branch, don't count this extra instruction.
// For -10 + {0, +, 1}:
// i = i + 1;
// cmp i, 10
//
// For {-10, +, 1}:
// i = i + 1;
- if (LU.Kind == LSRUse::ICmpZero && !F.hasZeroEnd())
+ if (LU.Kind == LSRUse::ICmpZero && !F.hasZeroEnd() && !TTI.canMacroFuseCmp())
C.Insns++;
// Each new AddRec adds 1 instruction to calculation.
C.Insns += (C.AddRecCost - PrevAddRecCost);