[llvm] [VectorCombine] foldBitcastShuffle - peek through any residual bitcasts before creating a new bitcast on top (PR #86119)
Simon Pilgrim via llvm-commits
llvm-commits at lists.llvm.org
Thu Mar 21 06:45:48 PDT 2024
https://github.com/RKSimon created https://github.com/llvm/llvm-project/pull/86119
Encountered while working on #67803, wading through the chains of bitcasts that SSE intrinsics introduces - this patch helps prevents cases where the bitcast chains aren't cleared out and we can't perform further combines until after InstCombine/InstSimplify has run.
I'm assuming we can't safely put this inside IRBuilderBase.CreateBitCast?
>From 89881d28b9df4a8dde063341f652cee5bd2d200c Mon Sep 17 00:00:00 2001
From: Simon Pilgrim <llvm-dev at redking.me.uk>
Date: Thu, 21 Mar 2024 13:41:56 +0000
Subject: [PATCH] [VectorCombine] foldBitcastShuffle - peek through any
residual bitcasts before creating a new bitcast on top
Encountered while working on #67803, this helps prevents cases where the bitcast chains aren't cleared out and we can't perform further combines until after InstCombine/InstSimplify has run.
I'm assuming we can't safely put this inside IRBuilderBase.CreateBitCast?
---
llvm/lib/Transforms/Vectorize/VectorCombine.cpp | 16 ++++++++++++++--
.../VectorCombine/X86/shuffle-inseltpoison.ll | 6 ++----
.../test/Transforms/VectorCombine/X86/shuffle.ll | 6 ++----
3 files changed, 18 insertions(+), 10 deletions(-)
diff --git a/llvm/lib/Transforms/Vectorize/VectorCombine.cpp b/llvm/lib/Transforms/Vectorize/VectorCombine.cpp
index 7e86137f23f3c8..87e05dde545cd5 100644
--- a/llvm/lib/Transforms/Vectorize/VectorCombine.cpp
+++ b/llvm/lib/Transforms/Vectorize/VectorCombine.cpp
@@ -135,6 +135,18 @@ class VectorCombine {
};
} // namespace
+/// Return the source operand of a potentially bitcasted value while
+/// optionally checking if it has one use. If there is no bitcast or the one
+/// use check is not met, return the input value itself.
+static Value *peekThroughBitcast(Value *V, bool OneUseOnly = false) {
+ if (auto *BitCast = dyn_cast<BitCastInst>(V))
+ if (!OneUseOnly || BitCast->hasOneUse())
+ return BitCast->getOperand(0);
+
+ // V is not a bitcast or V has more than one use and OneUseOnly is true.
+ return V;
+}
+
static bool canWidenLoad(LoadInst *Load, const TargetTransformInfo &TTI) {
// Do not widen load if atomic/volatile or under asan/hwasan/memtag/tsan.
// The widened load may load data from dirty regions or create data races
@@ -751,8 +763,8 @@ bool VectorCombine::foldBitcastShuffle(Instruction &I) {
// bitcast (shuf V0, V1, MaskC) --> shuf (bitcast V0), (bitcast V1), MaskC'
++NumShufOfBitcast;
- Value *CastV0 = Builder.CreateBitCast(V0, NewShuffleTy);
- Value *CastV1 = Builder.CreateBitCast(V1, NewShuffleTy);
+ Value *CastV0 = Builder.CreateBitCast(peekThroughBitcast(V0), NewShuffleTy);
+ Value *CastV1 = Builder.CreateBitCast(peekThroughBitcast(V1), NewShuffleTy);
Value *Shuf = Builder.CreateShuffleVector(CastV0, CastV1, NewMask);
replaceValue(I, *Shuf);
return true;
diff --git a/llvm/test/Transforms/VectorCombine/X86/shuffle-inseltpoison.ll b/llvm/test/Transforms/VectorCombine/X86/shuffle-inseltpoison.ll
index 8c5c6656ca1795..74a58c8d313611 100644
--- a/llvm/test/Transforms/VectorCombine/X86/shuffle-inseltpoison.ll
+++ b/llvm/test/Transforms/VectorCombine/X86/shuffle-inseltpoison.ll
@@ -133,8 +133,7 @@ define <2 x i64> @PR35454_1(<2 x i64> %v) {
; SSE-NEXT: ret <2 x i64> [[BC3]]
;
; AVX-LABEL: @PR35454_1(
-; AVX-NEXT: [[BC:%.*]] = bitcast <2 x i64> [[V:%.*]] to <4 x i32>
-; AVX-NEXT: [[TMP1:%.*]] = bitcast <4 x i32> [[BC]] to <16 x i8>
+; AVX-NEXT: [[TMP1:%.*]] = bitcast <2 x i64> [[V:%.*]] to <16 x i8>
; AVX-NEXT: [[BC1:%.*]] = shufflevector <16 x i8> [[TMP1]], <16 x i8> poison, <16 x i32> <i32 12, i32 13, i32 14, i32 15, i32 8, i32 9, i32 10, i32 11, i32 4, i32 5, i32 6, i32 7, i32 0, i32 1, i32 2, i32 3>
; AVX-NEXT: [[ADD:%.*]] = shl <16 x i8> [[BC1]], <i8 1, i8 1, i8 1, i8 1, i8 1, i8 1, i8 1, i8 1, i8 1, i8 1, i8 1, i8 1, i8 1, i8 1, i8 1, i8 1>
; AVX-NEXT: [[BC2:%.*]] = bitcast <16 x i8> [[ADD]] to <4 x i32>
@@ -164,8 +163,7 @@ define <2 x i64> @PR35454_2(<2 x i64> %v) {
; SSE-NEXT: ret <2 x i64> [[BC3]]
;
; AVX-LABEL: @PR35454_2(
-; AVX-NEXT: [[BC:%.*]] = bitcast <2 x i64> [[V:%.*]] to <4 x i32>
-; AVX-NEXT: [[TMP1:%.*]] = bitcast <4 x i32> [[BC]] to <8 x i16>
+; AVX-NEXT: [[TMP1:%.*]] = bitcast <2 x i64> [[V:%.*]] to <8 x i16>
; AVX-NEXT: [[BC1:%.*]] = shufflevector <8 x i16> [[TMP1]], <8 x i16> poison, <8 x i32> <i32 6, i32 7, i32 4, i32 5, i32 2, i32 3, i32 0, i32 1>
; AVX-NEXT: [[ADD:%.*]] = shl <8 x i16> [[BC1]], <i16 1, i16 1, i16 1, i16 1, i16 1, i16 1, i16 1, i16 1>
; AVX-NEXT: [[BC2:%.*]] = bitcast <8 x i16> [[ADD]] to <4 x i32>
diff --git a/llvm/test/Transforms/VectorCombine/X86/shuffle.ll b/llvm/test/Transforms/VectorCombine/X86/shuffle.ll
index 60cfc4d4b07079..d1484fd5ab3399 100644
--- a/llvm/test/Transforms/VectorCombine/X86/shuffle.ll
+++ b/llvm/test/Transforms/VectorCombine/X86/shuffle.ll
@@ -133,8 +133,7 @@ define <2 x i64> @PR35454_1(<2 x i64> %v) {
; SSE-NEXT: ret <2 x i64> [[BC3]]
;
; AVX-LABEL: @PR35454_1(
-; AVX-NEXT: [[BC:%.*]] = bitcast <2 x i64> [[V:%.*]] to <4 x i32>
-; AVX-NEXT: [[TMP1:%.*]] = bitcast <4 x i32> [[BC]] to <16 x i8>
+; AVX-NEXT: [[TMP1:%.*]] = bitcast <2 x i64> [[V:%.*]] to <16 x i8>
; AVX-NEXT: [[BC1:%.*]] = shufflevector <16 x i8> [[TMP1]], <16 x i8> poison, <16 x i32> <i32 12, i32 13, i32 14, i32 15, i32 8, i32 9, i32 10, i32 11, i32 4, i32 5, i32 6, i32 7, i32 0, i32 1, i32 2, i32 3>
; AVX-NEXT: [[ADD:%.*]] = shl <16 x i8> [[BC1]], <i8 1, i8 1, i8 1, i8 1, i8 1, i8 1, i8 1, i8 1, i8 1, i8 1, i8 1, i8 1, i8 1, i8 1, i8 1, i8 1>
; AVX-NEXT: [[BC2:%.*]] = bitcast <16 x i8> [[ADD]] to <4 x i32>
@@ -164,8 +163,7 @@ define <2 x i64> @PR35454_2(<2 x i64> %v) {
; SSE-NEXT: ret <2 x i64> [[BC3]]
;
; AVX-LABEL: @PR35454_2(
-; AVX-NEXT: [[BC:%.*]] = bitcast <2 x i64> [[V:%.*]] to <4 x i32>
-; AVX-NEXT: [[TMP1:%.*]] = bitcast <4 x i32> [[BC]] to <8 x i16>
+; AVX-NEXT: [[TMP1:%.*]] = bitcast <2 x i64> [[V:%.*]] to <8 x i16>
; AVX-NEXT: [[BC1:%.*]] = shufflevector <8 x i16> [[TMP1]], <8 x i16> poison, <8 x i32> <i32 6, i32 7, i32 4, i32 5, i32 2, i32 3, i32 0, i32 1>
; AVX-NEXT: [[ADD:%.*]] = shl <8 x i16> [[BC1]], <i16 1, i16 1, i16 1, i16 1, i16 1, i16 1, i16 1, i16 1>
; AVX-NEXT: [[BC2:%.*]] = bitcast <8 x i16> [[ADD]] to <4 x i32>
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