diff options
Diffstat (limited to 'llvm')
| -rw-r--r-- | llvm/lib/Transforms/InstCombine/InstCombineVectorOps.cpp | 5 | ||||
| -rw-r--r-- | llvm/test/Transforms/InstCombine/vec_shuffle.ll | 4 |
2 files changed, 7 insertions, 2 deletions
diff --git a/llvm/lib/Transforms/InstCombine/InstCombineVectorOps.cpp b/llvm/lib/Transforms/InstCombine/InstCombineVectorOps.cpp index abc2297f346..6889cd9189c 100644 --- a/llvm/lib/Transforms/InstCombine/InstCombineVectorOps.cpp +++ b/llvm/lib/Transforms/InstCombine/InstCombineVectorOps.cpp @@ -1498,6 +1498,11 @@ static Instruction *foldIdentityExtractShuffle(ShuffleVectorInst &Shuf) { if (!match(Op0, m_ShuffleVector(m_Value(X), m_Value(Y), m_Constant(Mask)))) return nullptr; + // Be conservative with shuffle transforms. If we can't kill the 1st shuffle, + // then combining may result in worse codegen. + if (!Op0->hasOneUse()) + return nullptr; + // We are extracting a subvector from a shuffle. Remove excess elements from // the 1st shuffle mask to eliminate the extract. // diff --git a/llvm/test/Transforms/InstCombine/vec_shuffle.ll b/llvm/test/Transforms/InstCombine/vec_shuffle.ll index 401bcee4991..aae337d0de3 100644 --- a/llvm/test/Transforms/InstCombine/vec_shuffle.ll +++ b/llvm/test/Transforms/InstCombine/vec_shuffle.ll @@ -195,7 +195,7 @@ define <4 x i8> @extract_subvector_of_shuffle_undefs_types(<2 x i8> %x, <2 x i8> ret <4 x i8> %extract_subv } -; FIXME: Extra uses are not ok - we should only do the transform when we can eliminate an instruction. +; Extra uses are not ok - we only do the transform when we can eliminate an instruction. declare void @use_v5i8(<5 x i8>) @@ -203,7 +203,7 @@ define <4 x i8> @extract_subvector_of_shuffle_extra_use(<2 x i8> %x, <2 x i8> %y ; CHECK-LABEL: @extract_subvector_of_shuffle_extra_use( ; CHECK-NEXT: [[SHUF:%.*]] = shufflevector <2 x i8> [[X:%.*]], <2 x i8> [[Y:%.*]], <5 x i32> <i32 undef, i32 2, i32 0, i32 1, i32 0> ; CHECK-NEXT: call void @use_v5i8(<5 x i8> [[SHUF]]) -; CHECK-NEXT: [[EXTRACT_SUBV:%.*]] = shufflevector <2 x i8> [[X]], <2 x i8> [[Y]], <4 x i32> <i32 undef, i32 2, i32 0, i32 undef> +; CHECK-NEXT: [[EXTRACT_SUBV:%.*]] = shufflevector <5 x i8> [[SHUF]], <5 x i8> undef, <4 x i32> <i32 0, i32 1, i32 2, i32 undef> ; CHECK-NEXT: ret <4 x i8> [[EXTRACT_SUBV]] ; %shuf = shufflevector <2 x i8> %x, <2 x i8> %y, <5 x i32> <i32 undef, i32 2, i32 0, i32 1, i32 0> |
