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[InstSimplify][InstCombine][ConstantFold] Move vector div/rem by zero fold to InstCombine #114280

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Merged
merged 3 commits into from
Nov 1, 2024
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[InstSimplify][InstCombine][ConstantFold] Move vector div/rem by zero fold to InstCombine #114280

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fed321f
[InstCombine] Add pre-commit tests. NFC.
dtcxzyw Oct 30, 2024
ed7dfec
[InstCombine] Move duplicate logic into `commonIDivRemTransforms`. NFC.
dtcxzyw Oct 31, 2024
e43b3b9
[InstSimplify][InstCombine][ConstantFold] Move vector div/rem by zero…
dtcxzyw Oct 31, 2024
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13 changes: 0 additions & 13 deletions llvm/lib/Analysis/InstructionSimplify.cpp
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Expand Up @@ -1095,19 +1095,6 @@ static Value *simplifyDivRem(Instruction::BinaryOps Opcode, Value *Op0,
if (match(Op1, m_Zero()))
return PoisonValue::get(Ty);

// If any element of a constant divisor fixed width vector is zero or undef
// the behavior is undefined and we can fold the whole op to poison.
auto *Op1C = dyn_cast<Constant>(Op1);
auto *VTy = dyn_cast<FixedVectorType>(Ty);
if (Op1C && VTy) {
unsigned NumElts = VTy->getNumElements();
for (unsigned i = 0; i != NumElts; ++i) {
Constant *Elt = Op1C->getAggregateElement(i);
if (Elt && (Elt->isNullValue() || Q.isUndefValue(Elt)))
return PoisonValue::get(Ty);
}
}

// poison / X -> poison
// poison % X -> poison
if (isa<PoisonValue>(Op0))
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5 changes: 0 additions & 5 deletions llvm/lib/IR/ConstantFold.cpp
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Expand Up @@ -902,11 +902,6 @@ Constant *llvm::ConstantFoldBinaryInstruction(unsigned Opcode, Constant *C1,
Constant *ExtractIdx = ConstantInt::get(Ty, i);
Constant *LHS = ConstantExpr::getExtractElement(C1, ExtractIdx);
Constant *RHS = ConstantExpr::getExtractElement(C2, ExtractIdx);

// If any element of a divisor vector is zero, the whole op is poison.
if (Instruction::isIntDivRem(Opcode) && RHS->isNullValue())
return PoisonValue::get(VTy);
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Could you just do Res = PoisonValue::get(RHS->getType()) and make a poison element?

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Isn't it handled by the scalar path? See test vec_select_udiv_poison. udiv <i32 42, i32 -7>, <i32 0, i32 1> is folded into <i32 poison, i32 -7>.


Constant *Res = ConstantExpr::isDesirableBinOp(Opcode)
? ConstantExpr::get(Opcode, LHS, RHS)
: ConstantFoldBinaryInstruction(Opcode, LHS, RHS);
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1 change: 1 addition & 0 deletions llvm/lib/Transforms/InstCombine/InstCombineInternal.h
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Expand Up @@ -102,6 +102,7 @@ class LLVM_LIBRARY_VISIBILITY InstCombinerImpl final
Instruction *visitSRem(BinaryOperator &I);
Instruction *visitFRem(BinaryOperator &I);
bool simplifyDivRemOfSelectWithZeroOp(BinaryOperator &I);
Instruction *commonIDivRemTransforms(BinaryOperator &I);
Instruction *commonIRemTransforms(BinaryOperator &I);
Instruction *commonIDivTransforms(BinaryOperator &I);
Instruction *visitUDiv(BinaryOperator &I);
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71 changes: 39 additions & 32 deletions llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
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Expand Up @@ -1158,29 +1158,39 @@ static Value *foldIDivShl(BinaryOperator &I, InstCombiner::BuilderTy &Builder) {
return nullptr;
}

/// This function implements the transforms common to both integer division
/// instructions (udiv and sdiv). It is called by the visitors to those integer
/// division instructions.
/// Common integer divide transforms
Instruction *InstCombinerImpl::commonIDivTransforms(BinaryOperator &I) {
if (Instruction *Phi = foldBinopWithPhiOperands(I))
return Phi;

/// Common integer divide/remainder transforms
Instruction *InstCombinerImpl::commonIDivRemTransforms(BinaryOperator &I) {
assert(I.isIntDivRem() && "Unexpected instruction");
Value *Op0 = I.getOperand(0), *Op1 = I.getOperand(1);
bool IsSigned = I.getOpcode() == Instruction::SDiv;

// If any element of a constant divisor fixed width vector is zero or undef
// the behavior is undefined and we can fold the whole op to poison.
auto *Op1C = dyn_cast<Constant>(Op1);
Type *Ty = I.getType();
auto *VTy = dyn_cast<FixedVectorType>(Ty);
if (Op1C && VTy) {
unsigned NumElts = VTy->getNumElements();
for (unsigned i = 0; i != NumElts; ++i) {
Constant *Elt = Op1C->getAggregateElement(i);
if (Elt && (Elt->isNullValue() || isa<UndefValue>(Elt)))
return replaceInstUsesWith(I, PoisonValue::get(Ty));
}
}

if (Instruction *Phi = foldBinopWithPhiOperands(I))
return Phi;

// The RHS is known non-zero.
if (Value *V = simplifyValueKnownNonZero(I.getOperand(1), *this, I))
return replaceOperand(I, 1, V);

// Handle cases involving: [su]div X, (select Cond, Y, Z)
// This does not apply for fdiv.
// Handle cases involving: div/rem X, (select Cond, Y, Z)
if (simplifyDivRemOfSelectWithZeroOp(I))
return &I;

// If the divisor is a select-of-constants, try to constant fold all div ops:
// C / (select Cond, TrueC, FalseC) --> select Cond, (C / TrueC), (C / FalseC)
// C div/rem (select Cond, TrueC, FalseC) --> select Cond, (C div/rem TrueC),
// (C div/rem FalseC)
// TODO: Adapt simplifyDivRemOfSelectWithZeroOp to allow this and other folds.
if (match(Op0, m_ImmConstant()) &&
match(Op1, m_Select(m_Value(), m_ImmConstant(), m_ImmConstant()))) {
Expand All @@ -1189,6 +1199,21 @@ Instruction *InstCombinerImpl::commonIDivTransforms(BinaryOperator &I) {
return R;
}

return nullptr;
}

/// This function implements the transforms common to both integer division
/// instructions (udiv and sdiv). It is called by the visitors to those integer
/// division instructions.
/// Common integer divide transforms
Instruction *InstCombinerImpl::commonIDivTransforms(BinaryOperator &I) {
if (Instruction *Res = commonIDivRemTransforms(I))
return Res;

Value *Op0 = I.getOperand(0), *Op1 = I.getOperand(1);
bool IsSigned = I.getOpcode() == Instruction::SDiv;
Type *Ty = I.getType();

const APInt *C2;
if (match(Op1, m_APInt(C2))) {
Value *X;
Expand Down Expand Up @@ -2138,29 +2163,11 @@ static Instruction *simplifyIRemMulShl(BinaryOperator &I,
/// remainder instructions.
/// Common integer remainder transforms
Instruction *InstCombinerImpl::commonIRemTransforms(BinaryOperator &I) {
if (Instruction *Phi = foldBinopWithPhiOperands(I))
return Phi;
if (Instruction *Res = commonIDivRemTransforms(I))
return Res;

Value *Op0 = I.getOperand(0), *Op1 = I.getOperand(1);

// The RHS is known non-zero.
if (Value *V = simplifyValueKnownNonZero(I.getOperand(1), *this, I))
return replaceOperand(I, 1, V);

// Handle cases involving: rem X, (select Cond, Y, Z)
if (simplifyDivRemOfSelectWithZeroOp(I))
return &I;

// If the divisor is a select-of-constants, try to constant fold all rem ops:
// C % (select Cond, TrueC, FalseC) --> select Cond, (C % TrueC), (C % FalseC)
// TODO: Adapt simplifyDivRemOfSelectWithZeroOp to allow this and other folds.
if (match(Op0, m_ImmConstant()) &&
match(Op1, m_Select(m_Value(), m_ImmConstant(), m_ImmConstant()))) {
if (Instruction *R = FoldOpIntoSelect(I, cast<SelectInst>(Op1),
/*FoldWithMultiUse*/ true))
return R;
}

if (isa<Constant>(Op1)) {
if (Instruction *Op0I = dyn_cast<Instruction>(Op0)) {
if (SelectInst *SI = dyn_cast<SelectInst>(Op0I)) {
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6 changes: 4 additions & 2 deletions llvm/test/Transforms/InstCombine/div.ll
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Expand Up @@ -1163,7 +1163,8 @@ define <2 x i8> @sdiv_constant_dividend_select_of_constants_divisor_vec(i1 %b) {

define <2 x i8> @sdiv_constant_dividend_select_of_constants_divisor_vec_ub1(i1 %b) {
; CHECK-LABEL: @sdiv_constant_dividend_select_of_constants_divisor_vec_ub1(
; CHECK-NEXT: ret <2 x i8> <i8 -10, i8 -10>
; CHECK-NEXT: [[R:%.*]] = select i1 [[B:%.*]], <2 x i8> <i8 poison, i8 8>, <2 x i8> <i8 -10, i8 -10>
; CHECK-NEXT: ret <2 x i8> [[R]]
;
%s = select i1 %b, <2 x i8> <i8 0, i8 -5>, <2 x i8> <i8 -4, i8 4>
%r = sdiv <2 x i8> <i8 42, i8 -42>, %s
Expand Down Expand Up @@ -1269,7 +1270,8 @@ define <2 x i8> @udiv_constant_dividend_select_of_constants_divisor_vec(i1 %b) {

define <2 x i8> @udiv_constant_dividend_select_of_constants_divisor_vec_ub1(i1 %b) {
; CHECK-LABEL: @udiv_constant_dividend_select_of_constants_divisor_vec_ub1(
; CHECK-NEXT: ret <2 x i8> <i8 0, i8 53>
; CHECK-NEXT: [[R:%.*]] = select i1 [[B:%.*]], <2 x i8> <i8 poison, i8 0>, <2 x i8> <i8 0, i8 53>
; CHECK-NEXT: ret <2 x i8> [[R]]
;
%s = select i1 %b, <2 x i8> <i8 0, i8 -5>, <2 x i8> <i8 -4, i8 4>
%r = udiv <2 x i8> <i8 42, i8 -42>, %s
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3 changes: 2 additions & 1 deletion llvm/test/Transforms/InstCombine/rem.ll
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Expand Up @@ -997,7 +997,8 @@ define <2 x i8> @urem_constant_dividend_select_of_constants_divisor_vec(i1 %b) {

define <2 x i8> @urem_constant_dividend_select_of_constants_divisor_vec_ub1(i1 %b) {
; CHECK-LABEL: @urem_constant_dividend_select_of_constants_divisor_vec_ub1(
; CHECK-NEXT: ret <2 x i8> <i8 42, i8 2>
; CHECK-NEXT: [[R:%.*]] = select i1 [[B:%.*]], <2 x i8> <i8 poison, i8 -42>, <2 x i8> <i8 42, i8 2>
; CHECK-NEXT: ret <2 x i8> [[R]]
;
%s = select i1 %b, <2 x i8> <i8 0, i8 -5>, <2 x i8> <i8 -4, i8 4>
%r = urem <2 x i8> <i8 42, i8 -42>, %s
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13 changes: 13 additions & 0 deletions llvm/test/Transforms/InstCombine/vector-udiv.ll
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Expand Up @@ -97,3 +97,16 @@ define <4 x i32> @test_v4i32_zext_shl_const_pow2(<4 x i32> %a0, <4 x i16> %a1) {
%3 = udiv <4 x i32> %a0, %2
ret <4 x i32> %3
}

; Make sure we do not simplify udiv <i32 42, i32 -7>, <i32 0, i32 1> to
; poison when threading udiv over selects

define <2 x i32> @vec_select_udiv_poison(<2 x i1> %x) {
; CHECK-LABEL: @vec_select_udiv_poison(
; CHECK-NEXT: [[DIV:%.*]] = select <2 x i1> [[X:%.*]], <2 x i32> zeroinitializer, <2 x i32> <i32 poison, i32 -7>
; CHECK-NEXT: ret <2 x i32> [[DIV]]
;
%sel = select <2 x i1> %x, <2 x i32> <i32 -1, i32 -1>, <2 x i32> <i32 0, i32 1>
%div = udiv <2 x i32> <i32 42, i32 -7>, %sel
ret <2 x i32> %div
}
16 changes: 10 additions & 6 deletions llvm/test/Transforms/InstSimplify/div.ll
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Expand Up @@ -29,47 +29,51 @@ define <2 x i32> @zero_dividend_vector_poison_elt(<2 x i32> %A) {

define <2 x i8> @sdiv_zero_elt_vec_constfold(<2 x i8> %x) {
; CHECK-LABEL: @sdiv_zero_elt_vec_constfold(
; CHECK-NEXT: ret <2 x i8> poison
; CHECK-NEXT: ret <2 x i8> <i8 poison, i8 0>
;
%div = sdiv <2 x i8> <i8 1, i8 2>, <i8 0, i8 -42>
ret <2 x i8> %div
}

define <2 x i8> @udiv_zero_elt_vec_constfold(<2 x i8> %x) {
; CHECK-LABEL: @udiv_zero_elt_vec_constfold(
; CHECK-NEXT: ret <2 x i8> poison
; CHECK-NEXT: ret <2 x i8> <i8 0, i8 poison>
;
%div = udiv <2 x i8> <i8 1, i8 2>, <i8 42, i8 0>
ret <2 x i8> %div
}

define <2 x i8> @sdiv_zero_elt_vec(<2 x i8> %x) {
; CHECK-LABEL: @sdiv_zero_elt_vec(
; CHECK-NEXT: ret <2 x i8> poison
; CHECK-NEXT: [[DIV:%.*]] = sdiv <2 x i8> [[X:%.*]], <i8 -42, i8 0>
; CHECK-NEXT: ret <2 x i8> [[DIV]]
;
%div = sdiv <2 x i8> %x, <i8 -42, i8 0>
ret <2 x i8> %div
}

define <2 x i8> @udiv_zero_elt_vec(<2 x i8> %x) {
; CHECK-LABEL: @udiv_zero_elt_vec(
; CHECK-NEXT: ret <2 x i8> poison
; CHECK-NEXT: [[DIV:%.*]] = udiv <2 x i8> [[X:%.*]], <i8 0, i8 42>
; CHECK-NEXT: ret <2 x i8> [[DIV]]
;
%div = udiv <2 x i8> %x, <i8 0, i8 42>
ret <2 x i8> %div
}

define <2 x i8> @sdiv_poison_elt_vec(<2 x i8> %x) {
; CHECK-LABEL: @sdiv_poison_elt_vec(
; CHECK-NEXT: ret <2 x i8> poison
; CHECK-NEXT: [[DIV:%.*]] = sdiv <2 x i8> [[X:%.*]], <i8 -42, i8 poison>
; CHECK-NEXT: ret <2 x i8> [[DIV]]
;
%div = sdiv <2 x i8> %x, <i8 -42, i8 poison>
ret <2 x i8> %div
}

define <2 x i8> @udiv_poison_elt_vec(<2 x i8> %x) {
; CHECK-LABEL: @udiv_poison_elt_vec(
; CHECK-NEXT: ret <2 x i8> poison
; CHECK-NEXT: [[DIV:%.*]] = udiv <2 x i8> [[X:%.*]], <i8 poison, i8 42>
; CHECK-NEXT: ret <2 x i8> [[DIV]]
;
%div = udiv <2 x i8> %x, <i8 poison, i8 42>
ret <2 x i8> %div
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16 changes: 10 additions & 6 deletions llvm/test/Transforms/InstSimplify/rem.ll
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Expand Up @@ -29,47 +29,51 @@ define <2 x i32> @zero_dividend_vector_poison_elt(<2 x i32> %A) {

define <2 x i8> @srem_zero_elt_vec_constfold(<2 x i8> %x) {
; CHECK-LABEL: @srem_zero_elt_vec_constfold(
; CHECK-NEXT: ret <2 x i8> poison
; CHECK-NEXT: ret <2 x i8> <i8 poison, i8 2>
;
%rem = srem <2 x i8> <i8 1, i8 2>, <i8 0, i8 -42>
ret <2 x i8> %rem
}

define <2 x i8> @urem_zero_elt_vec_constfold(<2 x i8> %x) {
; CHECK-LABEL: @urem_zero_elt_vec_constfold(
; CHECK-NEXT: ret <2 x i8> poison
; CHECK-NEXT: ret <2 x i8> <i8 1, i8 poison>
;
%rem = urem <2 x i8> <i8 1, i8 2>, <i8 42, i8 0>
ret <2 x i8> %rem
}

define <2 x i8> @srem_zero_elt_vec(<2 x i8> %x) {
; CHECK-LABEL: @srem_zero_elt_vec(
; CHECK-NEXT: ret <2 x i8> poison
; CHECK-NEXT: [[REM:%.*]] = srem <2 x i8> [[X:%.*]], <i8 -42, i8 0>
; CHECK-NEXT: ret <2 x i8> [[REM]]
;
%rem = srem <2 x i8> %x, <i8 -42, i8 0>
ret <2 x i8> %rem
}

define <2 x i8> @urem_zero_elt_vec(<2 x i8> %x) {
; CHECK-LABEL: @urem_zero_elt_vec(
; CHECK-NEXT: ret <2 x i8> poison
; CHECK-NEXT: [[REM:%.*]] = urem <2 x i8> [[X:%.*]], <i8 0, i8 42>
; CHECK-NEXT: ret <2 x i8> [[REM]]
;
%rem = urem <2 x i8> %x, <i8 0, i8 42>
ret <2 x i8> %rem
}

define <2 x i8> @srem_undef_elt_vec(<2 x i8> %x) {
; CHECK-LABEL: @srem_undef_elt_vec(
; CHECK-NEXT: ret <2 x i8> poison
; CHECK-NEXT: [[REM:%.*]] = srem <2 x i8> [[X:%.*]], <i8 -42, i8 undef>
; CHECK-NEXT: ret <2 x i8> [[REM]]
;
%rem = srem <2 x i8> %x, <i8 -42, i8 undef>
ret <2 x i8> %rem
}

define <2 x i8> @urem_undef_elt_vec(<2 x i8> %x) {
; CHECK-LABEL: @urem_undef_elt_vec(
; CHECK-NEXT: ret <2 x i8> poison
; CHECK-NEXT: [[REM:%.*]] = urem <2 x i8> [[X:%.*]], <i8 undef, i8 42>
; CHECK-NEXT: ret <2 x i8> [[REM]]
;
%rem = urem <2 x i8> %x, <i8 undef, i8 42>
ret <2 x i8> %rem
Expand Down
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