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[InstCombine] Support trunc to i1 in foldSelectICmpAnd #127905

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Merged
merged 1 commit into from
Mar 18, 2025
Merged

[InstCombine] Support trunc to i1 in foldSelectICmpAnd #127905

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65 changes: 38 additions & 27 deletions llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -119,7 +119,7 @@ static Instruction *foldSelectBinOpIdentity(SelectInst &Sel,
/// (shl (and (X, C1)), (log2(TC-FC) - log2(C1))) + FC
/// With some variations depending if FC is larger than TC, or the shift
/// isn't needed, or the bit widths don't match.
static Value *foldSelectICmpAnd(SelectInst &Sel, ICmpInst *Cmp,
static Value *foldSelectICmpAnd(SelectInst &Sel, Value *CondVal,
InstCombiner::BuilderTy &Builder,
const SimplifyQuery &SQ) {
const APInt *SelTC, *SelFC;
Expand All @@ -129,36 +129,47 @@ static Value *foldSelectICmpAnd(SelectInst &Sel, ICmpInst *Cmp,

// If this is a vector select, we need a vector compare.
Type *SelType = Sel.getType();
if (SelType->isVectorTy() != Cmp->getType()->isVectorTy())
if (SelType->isVectorTy() != CondVal->getType()->isVectorTy())
return nullptr;

Value *V;
APInt AndMask;
bool CreateAnd = false;
ICmpInst::Predicate Pred = Cmp->getPredicate();
if (ICmpInst::isEquality(Pred)) {
if (!match(Cmp->getOperand(1), m_Zero()))
return nullptr;
CmpPredicate Pred;
Value *CmpLHS, *CmpRHS;

V = Cmp->getOperand(0);
const APInt *AndRHS;
if (!match(V, m_And(m_Value(), m_Power2(AndRHS))))
return nullptr;
if (match(CondVal, m_ICmp(Pred, m_Value(CmpLHS), m_Value(CmpRHS)))) {
if (ICmpInst::isEquality(Pred)) {
if (!match(CmpRHS, m_Zero()))
return nullptr;

V = CmpLHS;
const APInt *AndRHS;
if (!match(V, m_And(m_Value(), m_Power2(AndRHS))))
return nullptr;

AndMask = *AndRHS;
} else if (auto Res = decomposeBitTestICmp(Cmp->getOperand(0),
Cmp->getOperand(1), Pred)) {
assert(ICmpInst::isEquality(Res->Pred) && "Not equality test?");
AndMask = Res->Mask;
V = Res->X;
KnownBits Known =
computeKnownBits(V, /*Depth=*/0, SQ.getWithInstruction(&Sel));
AndMask &= Known.getMaxValue();
if (!AndMask.isPowerOf2())
AndMask = *AndRHS;
} else if (auto Res = decomposeBitTestICmp(CmpLHS, CmpRHS, Pred)) {
assert(ICmpInst::isEquality(Res->Pred) && "Not equality test?");
AndMask = Res->Mask;
V = Res->X;
KnownBits Known =
computeKnownBits(V, /*Depth=*/0, SQ.getWithInstruction(&Sel));
AndMask &= Known.getMaxValue();
if (!AndMask.isPowerOf2())
return nullptr;

Pred = Res->Pred;
CreateAnd = true;
} else {
return nullptr;
}

Pred = Res->Pred;
CreateAnd = true;
} else if (auto *Trunc = dyn_cast<TruncInst>(CondVal)) {
V = Trunc->getOperand(0);
AndMask = APInt(V->getType()->getScalarSizeInBits(), 1);
Pred = ICmpInst::ICMP_NE;
CreateAnd = !Trunc->hasNoUnsignedWrap();
} else {
return nullptr;
}
Expand All @@ -176,7 +187,7 @@ static Value *foldSelectICmpAnd(SelectInst &Sel, ICmpInst *Cmp,
return nullptr;
// If we have to create an 'and', then we must kill the cmp to not
// increase the instruction count.
if (CreateAnd && !Cmp->hasOneUse())
if (CreateAnd && !CondVal->hasOneUse())
return nullptr;

// (V & AndMaskC) == 0 ? TC : FC --> TC | (V & AndMaskC)
Expand Down Expand Up @@ -217,7 +228,7 @@ static Value *foldSelectICmpAnd(SelectInst &Sel, ICmpInst *Cmp,
// a 'select' + 'icmp', then this transformation would result in more
// instructions and potentially interfere with other folding.
if (CreateAnd + ShouldNotVal + NeedShift + NeedZExtTrunc >
1 + Cmp->hasOneUse())
1 + CondVal->hasOneUse())
return nullptr;

// Insert the 'and' instruction on the input to the truncate.
Expand Down Expand Up @@ -1961,9 +1972,6 @@ Instruction *InstCombinerImpl::foldSelectInstWithICmp(SelectInst &SI,
tryToReuseConstantFromSelectInComparison(SI, *ICI, *this))
return NewSel;

if (Value *V = foldSelectICmpAnd(SI, ICI, Builder, SQ))
return replaceInstUsesWith(SI, V);

// NOTE: if we wanted to, this is where to detect integer MIN/MAX
bool Changed = false;
Value *TrueVal = SI.getTrueValue();
Expand Down Expand Up @@ -3961,6 +3969,9 @@ Instruction *InstCombinerImpl::visitSelectInst(SelectInst &SI) {
if (Instruction *Result = foldSelectInstWithICmp(SI, ICI))
return Result;

if (Value *V = foldSelectICmpAnd(SI, CondVal, Builder, SQ))
return replaceInstUsesWith(SI, V);

if (Value *V = foldSelectICmpAndBinOp(CondVal, TrueVal, FalseVal, Builder))
return replaceInstUsesWith(SI, V);

Expand Down
26 changes: 13 additions & 13 deletions llvm/test/Transforms/InstCombine/select-icmp-and.ll
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Original file line number Diff line number Diff line change
Expand Up @@ -809,8 +809,8 @@ define i8 @select_bittest_to_xor(i8 %x) {

define i8 @select_trunc_bittest_to_sub(i8 %x) {
; CHECK-LABEL: @select_trunc_bittest_to_sub(
; CHECK-NEXT: [[TRUNC:%.*]] = trunc i8 [[X:%.*]] to i1
; CHECK-NEXT: [[RET:%.*]] = select i1 [[TRUNC]], i8 3, i8 4
; CHECK-NEXT: [[TMP1:%.*]] = and i8 [[X:%.*]], 1
; CHECK-NEXT: [[RET:%.*]] = sub nuw nsw i8 4, [[TMP1]]
; CHECK-NEXT: ret i8 [[RET]]
;
%trunc = trunc i8 %x to i1
Expand All @@ -820,8 +820,7 @@ define i8 @select_trunc_bittest_to_sub(i8 %x) {

define i8 @select_trunc_nuw_bittest_to_sub(i8 %x) {
; CHECK-LABEL: @select_trunc_nuw_bittest_to_sub(
; CHECK-NEXT: [[TRUNC:%.*]] = trunc nuw i8 [[X:%.*]] to i1
; CHECK-NEXT: [[RET:%.*]] = select i1 [[TRUNC]], i8 3, i8 4
; CHECK-NEXT: [[RET:%.*]] = sub i8 4, [[X:%.*]]
; CHECK-NEXT: ret i8 [[RET]]
;
%trunc = trunc nuw i8 %x to i1
Expand All @@ -831,8 +830,8 @@ define i8 @select_trunc_nuw_bittest_to_sub(i8 %x) {

define i8 @select_trunc_nsw_bittest_to_sub(i8 %x) {
; CHECK-LABEL: @select_trunc_nsw_bittest_to_sub(
; CHECK-NEXT: [[TRUNC:%.*]] = trunc nsw i8 [[X:%.*]] to i1
; CHECK-NEXT: [[RET:%.*]] = select i1 [[TRUNC]], i8 3, i8 4
; CHECK-NEXT: [[TMP1:%.*]] = and i8 [[X:%.*]], 1
; CHECK-NEXT: [[RET:%.*]] = sub nuw nsw i8 4, [[TMP1]]
; CHECK-NEXT: ret i8 [[RET]]
;
%trunc = trunc nsw i8 %x to i1
Expand All @@ -844,7 +843,7 @@ define i8 @select_trunc_nuw_bittest_to_sub_extra_use(i8 %x) {
; CHECK-LABEL: @select_trunc_nuw_bittest_to_sub_extra_use(
; CHECK-NEXT: [[TRUNC:%.*]] = trunc nuw i8 [[X:%.*]] to i1
; CHECK-NEXT: call void @use1(i1 [[TRUNC]])
; CHECK-NEXT: [[RET:%.*]] = select i1 [[TRUNC]], i8 3, i8 4
; CHECK-NEXT: [[RET:%.*]] = sub i8 4, [[X]]
; CHECK-NEXT: ret i8 [[RET]]
;
%trunc = trunc nuw i8 %x to i1
Expand All @@ -868,8 +867,8 @@ define i8 @neg_select_trunc_bittest_to_sub_extra_use(i8 %x) {

define i8 @select_trunc_nuw_bittest_to_shl_not(i8 %x) {
; CHECK-LABEL: @select_trunc_nuw_bittest_to_shl_not(
; CHECK-NEXT: [[TRUNC:%.*]] = trunc nuw i8 [[X:%.*]] to i1
; CHECK-NEXT: [[RET:%.*]] = select i1 [[TRUNC]], i8 0, i8 4
; CHECK-NEXT: [[TMP1:%.*]] = shl i8 [[X:%.*]], 2
; CHECK-NEXT: [[RET:%.*]] = xor i8 [[TMP1]], 4
; CHECK-NEXT: ret i8 [[RET]]
;
%trunc = trunc nuw i8 %x to i1
Expand All @@ -879,8 +878,8 @@ define i8 @select_trunc_nuw_bittest_to_shl_not(i8 %x) {

define i8 @select_trunc_bittest_to_shl(i8 %x) {
; CHECK-LABEL: @select_trunc_bittest_to_shl(
; CHECK-NEXT: [[TRUNC:%.*]] = trunc i8 [[X:%.*]] to i1
; CHECK-NEXT: [[RET:%.*]] = select i1 [[TRUNC]], i8 4, i8 0
; CHECK-NEXT: [[TMP1:%.*]] = shl i8 [[X:%.*]], 2
; CHECK-NEXT: [[RET:%.*]] = and i8 [[TMP1]], 4
; CHECK-NEXT: ret i8 [[RET]]
;
%trunc = trunc i8 %x to i1
Expand All @@ -903,8 +902,9 @@ define i8 @neg_select_trunc_bittest_to_shl_extra_use(i8 %x) {

define i16 @select_trunc_nuw_bittest_or(i8 %x) {
; CHECK-LABEL: @select_trunc_nuw_bittest_or(
; CHECK-NEXT: [[TMP1:%.*]] = trunc nuw i8 [[X:%.*]] to i1
; CHECK-NEXT: [[RES:%.*]] = select i1 [[TMP1]], i16 20, i16 4
; CHECK-NEXT: [[TMP1:%.*]] = zext i8 [[X:%.*]] to i16
; CHECK-NEXT: [[SELECT:%.*]] = shl nuw nsw i16 [[TMP1]], 4
; CHECK-NEXT: [[RES:%.*]] = or disjoint i16 [[SELECT]], 4
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It is not a regression. The codegen without select is generally better: https://godbolt.org/z/1W6ocqdT3

; CHECK-NEXT: ret i16 [[RES]]
;
%trunc = trunc nuw i8 %x to i1
Expand Down
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