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[AggressiveInstcombine] Fold away shift in or reduction chain. #137875

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Merged
merged 1 commit into from
May 13, 2025
Merged

[AggressiveInstcombine] Fold away shift in or reduction chain. #137875

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57 changes: 57 additions & 0 deletions llvm/lib/Transforms/AggressiveInstCombine/AggressiveInstCombine.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -827,6 +827,62 @@ static bool foldConsecutiveLoads(Instruction &I, const DataLayout &DL,
return true;
}

/// Combine away instructions providing they are still equivalent when compared
/// against 0. i.e do they have any bits set.
static Value *optimizeShiftInOrChain(Value *V, IRBuilder<> &Builder) {
auto *I = dyn_cast<Instruction>(V);
if (!I || I->getOpcode() != Instruction::Or || !I->hasOneUse())
return nullptr;

Value *A;

// Look deeper into the chain of or's, combining away shl (so long as they are
// nuw or nsw).
Value *Op0 = I->getOperand(0);
if (match(Op0, m_CombineOr(m_NSWShl(m_Value(A), m_Value()),
m_NUWShl(m_Value(A), m_Value()))))
Op0 = A;
else if (auto *NOp = optimizeShiftInOrChain(Op0, Builder))
Op0 = NOp;

Value *Op1 = I->getOperand(1);
if (match(Op1, m_CombineOr(m_NSWShl(m_Value(A), m_Value()),
m_NUWShl(m_Value(A), m_Value()))))
Op1 = A;
else if (auto *NOp = optimizeShiftInOrChain(Op1, Builder))
Op1 = NOp;

if (Op0 != I->getOperand(0) || Op1 != I->getOperand(1))
return Builder.CreateOr(Op0, Op1);
return nullptr;
}

static bool foldICmpOrChain(Instruction &I, const DataLayout &DL,
TargetTransformInfo &TTI, AliasAnalysis &AA,
const DominatorTree &DT) {
CmpPredicate Pred;
Value *Op0;
if (!match(&I, m_ICmp(Pred, m_Value(Op0), m_Zero())) ||
!ICmpInst::isEquality(Pred))
return false;

// If the chain or or's matches a load, combine to that before attempting to
// remove shifts.
if (auto OpI = dyn_cast<Instruction>(Op0))
if (OpI->getOpcode() == Instruction::Or)
if (foldConsecutiveLoads(*OpI, DL, TTI, AA, DT))
return true;

IRBuilder<> Builder(&I);
// icmp eq/ne or(shl(a), b), 0 -> icmp eq/ne or(a, b), 0
if (auto *Res = optimizeShiftInOrChain(Op0, Builder)) {
I.replaceAllUsesWith(Builder.CreateICmp(Pred, Res, I.getOperand(1)));
return true;
}

return false;
}

// Calculate GEP Stride and accumulated const ModOffset. Return Stride and
// ModOffset
static std::pair<APInt, APInt>
Expand Down Expand Up @@ -1253,6 +1309,7 @@ static bool foldUnusualPatterns(Function &F, DominatorTree &DT,
MadeChange |= tryToRecognizeTableBasedCttz(I);
MadeChange |= foldConsecutiveLoads(I, DL, TTI, AA, DT);
MadeChange |= foldPatternedLoads(I, DL);
MadeChange |= foldICmpOrChain(I, DL, TTI, AA, DT);
// NOTE: This function introduces erasing of the instruction `I`, so it
// needs to be called at the end of this sequence, otherwise we may make
// bugs.
Expand Down
26 changes: 8 additions & 18 deletions llvm/test/Transforms/AggressiveInstCombine/or-shift-chain.ll
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Original file line number Diff line number Diff line change
Expand Up @@ -3,8 +3,7 @@

define i1 @remove_shift_nuw_ab(i8 %a, i8 %b, i8 %s) {
; CHECK-LABEL: @remove_shift_nuw_ab(
; CHECK-NEXT: [[T:%.*]] = shl nuw i8 [[A:%.*]], [[S:%.*]]
; CHECK-NEXT: [[OR:%.*]] = or i8 [[T]], [[B:%.*]]
; CHECK-NEXT: [[OR:%.*]] = or i8 [[T:%.*]], [[B:%.*]]
; CHECK-NEXT: [[IC:%.*]] = icmp eq i8 [[OR]], 0
; CHECK-NEXT: ret i1 [[IC]]
;
Expand All @@ -16,8 +15,7 @@ define i1 @remove_shift_nuw_ab(i8 %a, i8 %b, i8 %s) {

define i1 @remove_shift_nuw_ba(i8 %a, i8 %b, i8 %s) {
; CHECK-LABEL: @remove_shift_nuw_ba(
; CHECK-NEXT: [[T:%.*]] = shl nuw i8 [[A:%.*]], [[S:%.*]]
; CHECK-NEXT: [[OR:%.*]] = or i8 [[B:%.*]], [[T]]
; CHECK-NEXT: [[OR:%.*]] = or i8 [[B:%.*]], [[T:%.*]]
; CHECK-NEXT: [[IC:%.*]] = icmp eq i8 [[OR]], 0
; CHECK-NEXT: ret i1 [[IC]]
;
Expand All @@ -29,8 +27,7 @@ define i1 @remove_shift_nuw_ba(i8 %a, i8 %b, i8 %s) {

define i1 @remove_shift_nsw(i8 %a, i8 %b, i8 %s) {
; CHECK-LABEL: @remove_shift_nsw(
; CHECK-NEXT: [[T:%.*]] = shl nsw i8 [[A:%.*]], [[S:%.*]]
; CHECK-NEXT: [[OR:%.*]] = or i8 [[T]], [[B:%.*]]
; CHECK-NEXT: [[OR:%.*]] = or i8 [[T:%.*]], [[B:%.*]]
; CHECK-NEXT: [[IC:%.*]] = icmp eq i8 [[OR]], 0
; CHECK-NEXT: ret i1 [[IC]]
;
Expand All @@ -42,8 +39,7 @@ define i1 @remove_shift_nsw(i8 %a, i8 %b, i8 %s) {

define i1 @remove_shift_nuw_ne(i8 %a, i8 %b, i8 %s) {
; CHECK-LABEL: @remove_shift_nuw_ne(
; CHECK-NEXT: [[T:%.*]] = shl nuw i8 [[A:%.*]], [[S:%.*]]
; CHECK-NEXT: [[OR:%.*]] = or i8 [[T]], [[B:%.*]]
; CHECK-NEXT: [[OR:%.*]] = or i8 [[T:%.*]], [[B:%.*]]
; CHECK-NEXT: [[IC:%.*]] = icmp eq i8 [[OR]], 0
; CHECK-NEXT: ret i1 [[IC]]
;
Expand All @@ -55,8 +51,7 @@ define i1 @remove_shift_nuw_ne(i8 %a, i8 %b, i8 %s) {

define i1 @remove_shift_nsw_ne(i8 %a, i8 %b, i8 %s) {
; CHECK-LABEL: @remove_shift_nsw_ne(
; CHECK-NEXT: [[T:%.*]] = shl nsw i8 [[A:%.*]], [[S:%.*]]
; CHECK-NEXT: [[OR:%.*]] = or i8 [[T]], [[B:%.*]]
; CHECK-NEXT: [[OR:%.*]] = or i8 [[T:%.*]], [[B:%.*]]
; CHECK-NEXT: [[IC:%.*]] = icmp eq i8 [[OR]], 0
; CHECK-NEXT: ret i1 [[IC]]
;
Expand All @@ -81,9 +76,8 @@ define i1 @remove_shift_wraps(i8 %a, i8 %b, i8 %s) {

define i1 @remove_shift_chain_d(i8 %a, i8 %b, i8 %c, i8 %d, i8 %s) {
; CHECK-LABEL: @remove_shift_chain_d(
; CHECK-NEXT: [[DT:%.*]] = shl nuw i8 [[D:%.*]], [[S:%.*]]
; CHECK-NEXT: [[OR1:%.*]] = or i8 [[A:%.*]], [[B:%.*]]
; CHECK-NEXT: [[OR2:%.*]] = or i8 [[C:%.*]], [[DT]]
; CHECK-NEXT: [[OR2:%.*]] = or i8 [[C:%.*]], [[DT:%.*]]
; CHECK-NEXT: [[OR:%.*]] = or i8 [[OR1]], [[OR2]]
; CHECK-NEXT: [[IC:%.*]] = icmp eq i8 [[OR]], 0
; CHECK-NEXT: ret i1 [[IC]]
Expand All @@ -98,12 +92,8 @@ define i1 @remove_shift_chain_d(i8 %a, i8 %b, i8 %c, i8 %d, i8 %s) {

define i1 @remove_shift_chain_abcd(i8 %a, i8 %b, i8 %c, i8 %d, i8 %s) {
; CHECK-LABEL: @remove_shift_chain_abcd(
; CHECK-NEXT: [[AT:%.*]] = shl nuw i8 [[A:%.*]], [[S:%.*]]
; CHECK-NEXT: [[BT:%.*]] = shl nuw i8 [[B:%.*]], 2
; CHECK-NEXT: [[CT:%.*]] = shl nuw i8 [[C:%.*]], 1
; CHECK-NEXT: [[DT:%.*]] = shl nuw i8 [[D:%.*]], [[S]]
; CHECK-NEXT: [[OR1:%.*]] = or i8 [[AT]], [[BT]]
; CHECK-NEXT: [[OR2:%.*]] = or i8 [[CT]], [[DT]]
; CHECK-NEXT: [[OR1:%.*]] = or i8 [[AT:%.*]], [[BT:%.*]]
; CHECK-NEXT: [[OR2:%.*]] = or i8 [[CT:%.*]], [[DT:%.*]]
; CHECK-NEXT: [[OR:%.*]] = or i8 [[OR1]], [[OR2]]
; CHECK-NEXT: [[IC:%.*]] = icmp eq i8 [[OR]], 0
; CHECK-NEXT: ret i1 [[IC]]
Expand Down
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