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[LVI] Add trunc to i1 handling. #124480

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Merged
merged 1 commit into from
Feb 2, 2025
Merged

[LVI] Add trunc to i1 handling. #124480

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26 changes: 26 additions & 0 deletions llvm/lib/Analysis/LazyValueInfo.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -398,6 +398,8 @@ class LazyValueInfoImpl {
std::optional<ValueLatticeElement>
getValueFromICmpCondition(Value *Val, ICmpInst *ICI, bool isTrueDest,
bool UseBlockValue);
ValueLatticeElement getValueFromTrunc(Value *Val, TruncInst *Trunc,
bool IsTrueDest);

std::optional<ValueLatticeElement>
getValueFromCondition(Value *Val, Value *Cond, bool IsTrueDest,
Expand Down Expand Up @@ -1283,6 +1285,27 @@ std::optional<ValueLatticeElement> LazyValueInfoImpl::getValueFromICmpCondition(
return ValueLatticeElement::getOverdefined();
}

ValueLatticeElement LazyValueInfoImpl::getValueFromTrunc(Value *Val,
TruncInst *Trunc,
bool IsTrueDest) {
assert(Trunc->getType()->isIntOrIntVectorTy(1));

if (Trunc->getOperand(0) != Val)
return ValueLatticeElement::getOverdefined();

Type *Ty = Val->getType();

if (Trunc->hasNoUnsignedWrap()) {
if (IsTrueDest)
return ValueLatticeElement::get(ConstantInt::get(Ty, 1));
return ValueLatticeElement::get(Constant::getNullValue(Ty));
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You can use ConstantInt::getBool() here.

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I do not think it is not possible to use ConstantInt::getBool() as the type of val is not i1.
it is possible to swap the true case to ConstantInt::get(Ty, 1)

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You're right, I got confused with the types here. And yes, using ConstantInt::get is preferable. (getIntegerValue is a specialized API if you need to potentially create an inttoptr expression...)

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Fixed

}

if (IsTrueDest)
return ValueLatticeElement::getNot(Constant::getNullValue(Ty));
return ValueLatticeElement::getNot(Constant::getAllOnesValue(Ty));
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We could further improve these by taking the nowrap flags into account. I think in a lot of cases we'll have trunc nuw %x to i1, in which case if (trunc nuw %x to i1) implies %x == 1, not just %x != 0.

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added handling for nuw and update the proof

}

// Handle conditions of the form
// extractvalue(op.with.overflow(%x, C), 1).
static ValueLatticeElement getValueFromOverflowCondition(
Expand Down Expand Up @@ -1312,6 +1335,9 @@ LazyValueInfoImpl::getValueFromCondition(Value *Val, Value *Cond,
if (ICmpInst *ICI = dyn_cast<ICmpInst>(Cond))
return getValueFromICmpCondition(Val, ICI, IsTrueDest, UseBlockValue);

if (auto *Trunc = dyn_cast<TruncInst>(Cond))
return getValueFromTrunc(Val, Trunc, IsTrueDest);

if (auto *EVI = dyn_cast<ExtractValueInst>(Cond))
if (auto *WO = dyn_cast<WithOverflowInst>(EVI->getAggregateOperand()))
if (EVI->getNumIndices() == 1 && *EVI->idx_begin() == 1)
Expand Down
10 changes: 4 additions & 6 deletions llvm/test/Transforms/CorrelatedValuePropagation/cond-at-use.ll
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Expand Up @@ -557,9 +557,8 @@ define i16 @and_elide(i16 noundef %x) {

define i16 @and_elide_trunc_cond(i16 noundef %x) {
; CHECK-LABEL: @and_elide_trunc_cond(
; CHECK-NEXT: [[AND:%.*]] = and i16 [[X:%.*]], 1
; CHECK-NEXT: [[CMP:%.*]] = trunc nuw i16 [[X]] to i1
; CHECK-NEXT: [[SEL:%.*]] = select i1 [[CMP]], i16 [[AND]], i16 24
; CHECK-NEXT: [[CMP:%.*]] = trunc nuw i16 [[X:%.*]] to i1
; CHECK-NEXT: [[SEL:%.*]] = select i1 [[CMP]], i16 [[X]], i16 24
; CHECK-NEXT: ret i16 [[SEL]]
;
%and = and i16 %x, 1
Expand All @@ -570,9 +569,8 @@ define i16 @and_elide_trunc_cond(i16 noundef %x) {

define <2 x i8> @and_elide_trunc_cond_vec(<2 x i8> noundef %x) {
; CHECK-LABEL: @and_elide_trunc_cond_vec(
; CHECK-NEXT: [[AND:%.*]] = and <2 x i8> [[X:%.*]], splat (i8 1)
; CHECK-NEXT: [[CMP:%.*]] = trunc nuw <2 x i8> [[X]] to <2 x i1>
; CHECK-NEXT: [[SEL:%.*]] = select <2 x i1> [[CMP]], <2 x i8> [[AND]], <2 x i8> splat (i8 24)
; CHECK-NEXT: [[CMP:%.*]] = trunc nuw <2 x i8> [[X:%.*]] to <2 x i1>
; CHECK-NEXT: [[SEL:%.*]] = select <2 x i1> [[CMP]], <2 x i8> [[X]], <2 x i8> splat (i8 24)
; CHECK-NEXT: ret <2 x i8> [[SEL]]
;
%and = and <2 x i8> %x, splat (i8 1)
Expand Down
36 changes: 12 additions & 24 deletions llvm/test/Transforms/CorrelatedValuePropagation/icmp.ll
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Expand Up @@ -1515,10 +1515,8 @@ define void @test_trunc_bittest(i8 %a) {
; CHECK-NEXT: [[TRUNC:%.*]] = trunc i8 [[A:%.*]] to i1
; CHECK-NEXT: br i1 [[TRUNC]], label [[IF_TRUE:%.*]], label [[IF_FALSE:%.*]]
; CHECK: if.true:
; CHECK-NEXT: [[CMP1:%.*]] = icmp ne i8 [[A]], 0
; CHECK-NEXT: call void @check1(i1 [[CMP1]])
; CHECK-NEXT: [[CMP2:%.*]] = icmp eq i8 [[A]], 0
; CHECK-NEXT: call void @check1(i1 [[CMP2]])
; CHECK-NEXT: call void @check1(i1 true)
; CHECK-NEXT: call void @check1(i1 false)
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We should also have negative tests, e.g. to show that it does not imply == 1.

; CHECK-NEXT: [[CMP3:%.*]] = icmp ne i8 [[A]], 1
; CHECK-NEXT: call void @check1(i1 [[CMP3]])
; CHECK-NEXT: [[CMP4:%.*]] = icmp eq i8 [[A]], 1
Expand Down Expand Up @@ -1559,10 +1557,8 @@ define void @test_trunc_not_bittest(i8 %a) {
; CHECK-NEXT: [[NOT:%.*]] = xor i1 [[TRUNC]], true
; CHECK-NEXT: br i1 [[NOT]], label [[IF_FALSE:%.*]], label [[IF_TRUE:%.*]]
; CHECK: if.true:
; CHECK-NEXT: [[CMP1:%.*]] = icmp ne i8 [[A]], -1
; CHECK-NEXT: call void @check1(i1 [[CMP1]])
; CHECK-NEXT: [[CMP2:%.*]] = icmp eq i8 [[A]], -1
; CHECK-NEXT: call void @check1(i1 [[CMP2]])
; CHECK-NEXT: call void @check1(i1 true)
; CHECK-NEXT: call void @check1(i1 false)
; CHECK-NEXT: [[CMP3:%.*]] = icmp ne i8 [[A]], 0
; CHECK-NEXT: call void @check1(i1 [[CMP3]])
; CHECK-NEXT: [[CMP4:%.*]] = icmp eq i8 [[A]], 0
Expand Down Expand Up @@ -1603,14 +1599,10 @@ define void @test_trunc_nuw_bittest(i8 %a) {
; CHECK-NEXT: [[TRUNC:%.*]] = trunc nuw i8 [[A:%.*]] to i1
; CHECK-NEXT: br i1 [[TRUNC]], label [[IF_TRUE:%.*]], label [[IF_FALSE:%.*]]
; CHECK: if.true:
; CHECK-NEXT: [[CMP1:%.*]] = icmp ne i8 [[A]], 0
; CHECK-NEXT: call void @check1(i1 [[CMP1]])
; CHECK-NEXT: [[CMP2:%.*]] = icmp eq i8 [[A]], 0
; CHECK-NEXT: call void @check1(i1 [[CMP2]])
; CHECK-NEXT: [[CMP3:%.*]] = icmp ne i8 [[A]], 1
; CHECK-NEXT: call void @check1(i1 [[CMP3]])
; CHECK-NEXT: [[CMP4:%.*]] = icmp eq i8 [[A]], 1
; CHECK-NEXT: call void @check1(i1 [[CMP4]])
; CHECK-NEXT: call void @check1(i1 true)
; CHECK-NEXT: call void @check1(i1 false)
; CHECK-NEXT: call void @check1(i1 false)
; CHECK-NEXT: call void @check1(i1 true)
; CHECK-NEXT: ret void
; CHECK: if.false:
; CHECK-NEXT: ret void
Expand Down Expand Up @@ -1639,14 +1631,10 @@ define void @test_trunc_nuw_not_bittest(i8 %a) {
; CHECK-NEXT: [[NOT:%.*]] = xor i1 [[TRUNC]], true
; CHECK-NEXT: br i1 [[NOT]], label [[IF_TRUE:%.*]], label [[IF_FALSE:%.*]]
; CHECK: if.true:
; CHECK-NEXT: [[CMP1:%.*]] = icmp ne i8 [[A]], 0
; CHECK-NEXT: call void @check1(i1 [[CMP1]])
; CHECK-NEXT: [[CMP2:%.*]] = icmp eq i8 [[A]], 0
; CHECK-NEXT: call void @check1(i1 [[CMP2]])
; CHECK-NEXT: [[CMP3:%.*]] = icmp ne i8 [[A]], 1
; CHECK-NEXT: call void @check1(i1 [[CMP3]])
; CHECK-NEXT: [[CMP4:%.*]] = icmp eq i8 [[A]], 1
; CHECK-NEXT: call void @check1(i1 [[CMP4]])
; CHECK-NEXT: call void @check1(i1 false)
; CHECK-NEXT: call void @check1(i1 true)
; CHECK-NEXT: call void @check1(i1 true)
; CHECK-NEXT: call void @check1(i1 false)
; CHECK-NEXT: ret void
; CHECK: if.false:
; CHECK-NEXT: ret void
Expand Down