Commit ffc3fb66 authored by Christudasan Devadasan's avatar Christudasan Devadasan
Browse files

SROA: Enhance speculateSelectInstLoads 

Allow the folding even if there is an
intervening bitcast.

Reviewed By: arsenm

Differential Revision: https://reviews.llvm.org/D106667
parent a00aafc3

llvm/lib/Transforms/Scalar/SROA.cpp

+26 −3
Original line number Diff line number Diff line
@@ -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<LoadInst>(U);

    LoadInst *LI;

    BitCastInst *BC = dyn_cast<BitCastInst>(U);

    if (BC && BC->hasOneUse())

      LI = dyn_cast<LoadInst>(*BC->user_begin());

    else

      LI = dyn_cast<LoadInst>(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<LoadInst>(SI.user_back());

    LoadInst *LI;

    BitCastInst *BC = dyn_cast<BitCastInst>(SI.user_back());

    if (BC) {

      assert(BC->hasOneUse() && "Bitcast should have a single use.");

      LI = cast<LoadInst>(BC->user_back());

    } else {

      LI = cast<LoadInst>(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();

}

llvm/test/Transforms/SROA/phi-and-select.ll

+5 −14
Original line number Diff line number Diff line
@@ -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]

llvm/test/Transforms/SROA/select-load.ll

0 → 100644
+35 −0
Original line number Diff line number Diff line 
; 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

}