From ffc3fb665d0a0dccd64cc8c803ad8cc1a0d5dfa1 Mon Sep 17 00:00:00 2001 From: Christudasan Devadasan Date: Fri, 23 Jul 2021 08:28:55 -0400 Subject: [PATCH] SROA: Enhance speculateSelectInstLoads Allow the folding even if there is an intervening bitcast. Reviewed By: arsenm Differential Revision: https://reviews.llvm.org/D106667 --- llvm/lib/Transforms/Scalar/SROA.cpp | 29 +++++++++++++++-- llvm/test/Transforms/SROA/phi-and-select.ll | 19 +++-------- llvm/test/Transforms/SROA/select-load.ll | 35 +++++++++++++++++++++ 3 files changed, 66 insertions(+), 17 deletions(-) create mode 100644 llvm/test/Transforms/SROA/select-load.ll diff --git a/llvm/lib/Transforms/Scalar/SROA.cpp b/llvm/lib/Transforms/Scalar/SROA.cpp index b3c4308ae80c..4a6bf97602e5 100644 --- a/llvm/lib/Transforms/Scalar/SROA.cpp +++ b/llvm/lib/Transforms/Scalar/SROA.cpp @@ -1330,14 +1330,21 @@ static void speculatePHINodeLoads(PHINode &PN) { /// %V = select i1 %cond, i32 %V1, i32 %V2 /// /// We can do this to a select if its only uses are loads and if the operand -/// to the select can be loaded unconditionally. +/// to the select can be loaded unconditionally. If found an intervening bitcast +/// with a single use of the load, allow the promotion. static bool isSafeSelectToSpeculate(SelectInst &SI) { Value *TValue = SI.getTrueValue(); Value *FValue = SI.getFalseValue(); const DataLayout &DL = SI.getModule()->getDataLayout(); for (User *U : SI.users()) { - LoadInst *LI = dyn_cast(U); + LoadInst *LI; + BitCastInst *BC = dyn_cast(U); + if (BC && BC->hasOneUse()) + LI = dyn_cast(*BC->user_begin()); + else + LI = dyn_cast(U); + if (!LI || !LI->isSimple()) return false; @@ -1363,10 +1370,24 @@ static void speculateSelectInstLoads(SelectInst &SI) { Value *FV = SI.getFalseValue(); // Replace the loads of the select with a select of two loads. while (!SI.use_empty()) { - LoadInst *LI = cast(SI.user_back()); + LoadInst *LI; + BitCastInst *BC = dyn_cast(SI.user_back()); + if (BC) { + assert(BC->hasOneUse() && "Bitcast should have a single use."); + LI = cast(BC->user_back()); + } else { + LI = cast(SI.user_back()); + } + assert(LI->isSimple() && "We only speculate simple loads"); IRB.SetInsertPoint(LI); + if (BC) { + // Cast the operands to bitcast's target type. + TV = IRB.CreateBitCast(TV, BC->getType(), TV->getName() + ".sroa.cast"); + FV = IRB.CreateBitCast(FV, BC->getType(), FV->getName() + ".sroa.cast"); + } + LoadInst *TL = IRB.CreateLoad(LI->getType(), TV, LI->getName() + ".sroa.speculate.load.true"); LoadInst *FL = IRB.CreateLoad(LI->getType(), FV, @@ -1390,6 +1411,8 @@ static void speculateSelectInstLoads(SelectInst &SI) { LLVM_DEBUG(dbgs() << " speculated to: " << *V << "\n"); LI->replaceAllUsesWith(V); LI->eraseFromParent(); + if (BC) + BC->eraseFromParent(); } SI.eraseFromParent(); } diff --git a/llvm/test/Transforms/SROA/phi-and-select.ll b/llvm/test/Transforms/SROA/phi-and-select.ll index c77371498135..d1863359b163 100644 --- a/llvm/test/Transforms/SROA/phi-and-select.ll +++ b/llvm/test/Transforms/SROA/phi-and-select.ll @@ -60,23 +60,14 @@ entry: ret i32 %result } -; If bitcast isn't considered a safe phi/select use, the alloca -; remains as an array. -; FIXME: Why isn't this identical to test2? define float @test2_bitcast() { ; CHECK-LABEL: @test2_bitcast( ; CHECK-NEXT: entry: -; CHECK-NEXT: [[A_SROA_0:%.*]] = alloca i32, align 4 -; CHECK-NEXT: [[A_SROA_3:%.*]] = alloca i32, align 4 -; CHECK-NEXT: store i32 0, i32* [[A_SROA_0]], align 4 -; CHECK-NEXT: store i32 1, i32* [[A_SROA_3]], align 4 -; CHECK-NEXT: [[A_SROA_0_0_A_SROA_0_0_V0:%.*]] = load i32, i32* [[A_SROA_0]], align 4 -; CHECK-NEXT: [[A_SROA_3_0_A_SROA_3_4_V1:%.*]] = load i32, i32* [[A_SROA_3]], align 4 -; CHECK-NEXT: [[COND:%.*]] = icmp sle i32 [[A_SROA_0_0_A_SROA_0_0_V0]], [[A_SROA_3_0_A_SROA_3_4_V1]] -; CHECK-NEXT: [[SELECT:%.*]] = select i1 [[COND]], i32* [[A_SROA_3]], i32* [[A_SROA_0]] -; CHECK-NEXT: [[SELECT_BC:%.*]] = bitcast i32* [[SELECT]] to float* -; CHECK-NEXT: [[RESULT:%.*]] = load float, float* [[SELECT_BC]], align 4 -; CHECK-NEXT: ret float [[RESULT]] +; CHECK-NEXT: [[COND:%.*]] = icmp sle i32 0, 1 +; CHECK-NEXT: [[TMP0:%.*]] = bitcast i32 1 to float +; CHECK-NEXT: [[TMP1:%.*]] = bitcast i32 0 to float +; CHECK-NEXT: [[RESULT_SROA_SPECULATED:%.*]] = select i1 [[COND]], float [[TMP0]], float [[TMP1]] +; CHECK-NEXT: ret float [[RESULT_SROA_SPECULATED]] ; entry: %a = alloca [2 x i32] diff --git a/llvm/test/Transforms/SROA/select-load.ll b/llvm/test/Transforms/SROA/select-load.ll new file mode 100644 index 000000000000..60cbae4fb1e5 --- /dev/null +++ b/llvm/test/Transforms/SROA/select-load.ll @@ -0,0 +1,35 @@ +; NOTE: Assertions have been autogenerated by utils/update_test_checks.py +; RUN: opt -S -sroa < %s | FileCheck %s + +%st.half = type { half } + +; Allow speculateSelectInstLoads to fold load and select +; even if there is an intervening bitcast. +define <2 x i16> @test_load_bitcast_select(i1 %cond1, i1 %cond2) { +; CHECK-LABEL: @test_load_bitcast_select( +; CHECK-NEXT: [[TMP1:%.*]] = bitcast half 0xHFFFF to i16 +; CHECK-NEXT: [[TMP2:%.*]] = bitcast half 0xH0000 to i16 +; CHECK-NEXT: [[LD1_SROA_SPECULATED:%.*]] = select i1 [[COND1:%.*]], i16 [[TMP1]], i16 [[TMP2]] +; CHECK-NEXT: [[V1:%.*]] = insertelement <2 x i16> undef, i16 [[LD1_SROA_SPECULATED]], i32 0 +; CHECK-NEXT: [[TMP3:%.*]] = bitcast half 0xHFFFF to i16 +; CHECK-NEXT: [[TMP4:%.*]] = bitcast half 0xH0000 to i16 +; CHECK-NEXT: [[LD2_SROA_SPECULATED:%.*]] = select i1 [[COND2:%.*]], i16 [[TMP3]], i16 [[TMP4]] +; CHECK-NEXT: [[V2:%.*]] = insertelement <2 x i16> [[V1]], i16 [[LD2_SROA_SPECULATED]], i32 1 +; CHECK-NEXT: ret <2 x i16> [[V2]] +; + %true = alloca half, align 2 + %false = alloca half, align 2 + store half 0xHFFFF, half* %true, align 2 + store half 0xH0000, half* %false, align 2 + %false.cast = bitcast half* %false to %st.half* + %true.cast = bitcast half* %true to %st.half* + %sel1 = select i1 %cond1, %st.half* %true.cast, %st.half* %false.cast + %cast1 = bitcast %st.half* %sel1 to i16* + %ld1 = load i16, i16* %cast1, align 2 + %v1 = insertelement <2 x i16> undef, i16 %ld1, i32 0 + %sel2 = select i1 %cond2, %st.half* %true.cast, %st.half* %false.cast + %cast2 = bitcast %st.half* %sel2 to i16* + %ld2 = load i16, i16* %cast2, align 2 + %v2 = insertelement <2 x i16> %v1, i16 %ld2, i32 1 + ret <2 x i16> %v2 +}