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[GISel] Lower scalar G_SELECT in LegalizerHelper #79342

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Merged
merged 1 commit into from
Jan 26, 2024
Merged

[GISel] Lower scalar G_SELECT in LegalizerHelper #79342

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25 changes: 15 additions & 10 deletions llvm/lib/CodeGen/GlobalISel/LegalizerHelper.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -7946,13 +7946,11 @@ LegalizerHelper::lowerISFPCLASS(MachineInstr &MI) {
}

LegalizerHelper::LegalizeResult LegalizerHelper::lowerSelect(MachineInstr &MI) {
// Implement vector G_SELECT in terms of XOR, AND, OR.
// Implement G_SELECT in terms of XOR, AND, OR.
auto [DstReg, DstTy, MaskReg, MaskTy, Op1Reg, Op1Ty, Op2Reg, Op2Ty] =
MI.getFirst4RegLLTs();
if (!DstTy.isVector())
return UnableToLegalize;

bool IsEltPtr = DstTy.getElementType().isPointer();
bool IsEltPtr = DstTy.getScalarType().isPointer();
if (IsEltPtr) {
LLT ScalarPtrTy = LLT::scalar(DstTy.getScalarSizeInBits());
LLT NewTy = DstTy.changeElementType(ScalarPtrTy);
Expand All @@ -7962,7 +7960,7 @@ LegalizerHelper::LegalizeResult LegalizerHelper::lowerSelect(MachineInstr &MI) {
}

if (MaskTy.isScalar()) {
// Turn the scalar condition into a vector condition mask.
// Turn the scalar condition into a vector condition mask if needed.

Register MaskElt = MaskReg;

Expand All @@ -7972,13 +7970,20 @@ LegalizerHelper::LegalizeResult LegalizerHelper::lowerSelect(MachineInstr &MI) {
MaskElt = MIRBuilder.buildSExtInReg(MaskTy, MaskElt, 1).getReg(0);

// Continue the sign extension (or truncate) to match the data type.
MaskElt = MIRBuilder.buildSExtOrTrunc(DstTy.getElementType(),
MaskElt).getReg(0);
MaskElt =
MIRBuilder.buildSExtOrTrunc(DstTy.getScalarType(), MaskElt).getReg(0);

// Generate a vector splat idiom.
auto ShufSplat = MIRBuilder.buildShuffleSplat(DstTy, MaskElt);
MaskReg = ShufSplat.getReg(0);
if (DstTy.isVector()) {
// Generate a vector splat idiom.
auto ShufSplat = MIRBuilder.buildShuffleSplat(DstTy, MaskElt);
MaskReg = ShufSplat.getReg(0);
} else {
MaskReg = MaskElt;
}
MaskTy = DstTy;
} else if (!DstTy.isVector()) {
// Cannot handle the case that mask is a vector and dst is a scalar.
return UnableToLegalize;
}

if (MaskTy.getSizeInBits() != DstTy.getSizeInBits()) {
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41 changes: 41 additions & 0 deletions llvm/unittests/CodeGen/GlobalISel/LegalizerHelperTest.cpp
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Expand Up @@ -3431,6 +3431,47 @@ TEST_F(AArch64GISelMITest, LowerUDIVREM) {
EXPECT_TRUE(CheckMachineFunction(*MF, CheckStr)) << *MF;
}

// Test G_SELECT lowering.
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It might be good to add a comment to say we don't expect to legalize scalar selects on aarch64 like this, but it is useful for testing.

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Good point, added a comment.

// Note: This is for testing the legalizer, aarch64 does not lower scalar
// selects like this.
TEST_F(AArch64GISelMITest, LowerSelect) {
setUp();
if (!TM)
GTEST_SKIP();

// Declare your legalization info
DefineLegalizerInfo(A, { getActionDefinitionsBuilder(G_SELECT).lower(); });

LLT S1 = LLT::scalar(1);
LLT S32 = LLT::scalar(32);
auto Tst = B.buildTrunc(S1, Copies[0]);
auto SrcA = B.buildTrunc(S32, Copies[1]);
auto SrcB = B.buildTrunc(S32, Copies[2]);
auto SELECT = B.buildInstr(TargetOpcode::G_SELECT, {S32}, {Tst, SrcA, SrcB});

AInfo Info(MF->getSubtarget());
DummyGISelObserver Observer;
LegalizerHelper Helper(*MF, Info, Observer, B);
// Perform Legalization
EXPECT_EQ(LegalizerHelper::LegalizeResult::Legalized,
Helper.lower(*SELECT, 0, S32));

auto CheckStr = R"(
CHECK: [[TST:%[0-9]+]]:_(s1) = G_TRUNC
CHECK: [[TRUE:%[0-9]+]]:_(s32) = G_TRUNC
CHECK: [[FALSE:%[0-9]+]]:_(s32) = G_TRUNC
CHECK: [[MSK:%[0-9]+]]:_(s32) = G_SEXT [[TST]]
CHECK: [[M:%[0-9]+]]:_(s32) = G_CONSTANT i32 -1
CHECK: [[NEGMSK:%[0-9]+]]:_(s32) = G_XOR [[MSK]]:_, [[M]]:_
CHECK: [[TVAL:%[0-9]+]]:_(s32) = G_AND [[TRUE]]:_, [[MSK]]:_
CHECK: [[FVAL:%[0-9]+]]:_(s32) = G_AND [[FALSE]]:_, [[NEGMSK]]:_
CHECK: [[RES:%[0-9]+]]:_(s32) = G_OR [[TVAL]]:_, [[FVAL]]:_
)";

// Check
EXPECT_TRUE(CheckMachineFunction(*MF, CheckStr)) << *MF;
}

// Test widening of G_UNMERGE_VALUES
TEST_F(AArch64GISelMITest, WidenUnmerge) {
setUp();
Expand Down