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InstCombine: fold(select C, (X | A), X) | B into X | select C, (A | B), B. (#154246) #154267

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InstCombine: fold(select C, (X | A), X) | B into X | select C, (A | B), B. (#154246) #154267

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70 changes: 70 additions & 0 deletions llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -2695,6 +2695,40 @@ Instruction *InstCombinerImpl::visitAnd(BinaryOperator &I) {
if (Instruction *FoldedLogic = foldBinOpIntoSelectOrPhi(I))
return FoldedLogic;

// Factor a common operand across select feeding an 'or':
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Any reason for duplicating the code in visitAnd?

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Hello,
while working on the optimization for the OR operation , I rewrite the expression from (select C, (X | A), X) | B to select C, (A | B),B. The same OR optimization can be used to rewrite AND operations as well. Instead of overengineering , I thought of duplicating it for AND operations.

if not required for AND operations, the code can be discarded.

// (select Cond, (X | A), X) | B -> X | select Cond, (A | B), B
// (select Cond, X, (X | A)) | B -> X | select Cond, B, (A | B)
// and commuted variants swapping the operands of the outer 'or'.
auto TryFactorSelectOr = [&](Value *SelOp, Value *OtherOp) -> Instruction * {
auto *SI = dyn_cast<SelectInst>(SelOp);
if (!SI)
return nullptr;

Value *Cond = SI->getCondition();
Value *T = SI->getTrueValue();
Value *F = SI->getFalseValue();
Value *X, *A;

// Match: select Cond, (X|A), X
if (match(T, m_c_Or(m_Value(X), m_Value(A))) && F == X) {
Value *AorB = Builder.CreateOr(A, OtherOp);
Value *InnerSel = Builder.CreateSelect(Cond, AorB, OtherOp);
return BinaryOperator::CreateOr(X, InnerSel);
}
// Match: select Cond, X, (X|A)
if (match(F, m_c_Or(m_Value(X), m_Value(A))) && T == X) {
Value *AorB = Builder.CreateOr(A, OtherOp);
Value *InnerSel = Builder.CreateSelect(Cond, OtherOp, AorB);
return BinaryOperator::CreateOr(X, InnerSel);
}
return nullptr;
};

if (Instruction *R = TryFactorSelectOr(Op0, Op1))
return R;
if (Instruction *R = TryFactorSelectOr(Op1, Op0))
return R;

if (Instruction *DeMorgan = matchDeMorgansLaws(I, *this))
return DeMorgan;

Expand Down Expand Up @@ -4022,6 +4056,42 @@ Instruction *InstCombinerImpl::visitOr(BinaryOperator &I) {
}
}

// Factor a common operand across select feeding an 'or' before pushing the
// constant into the select arms:
// (select Cond, (X | A), X) | B -> X | select Cond, (A | B), B
// (select Cond, X, (X | A)) | B -> X | select Cond, B, (A | B)
// and commuted variants swapping the operands of the outer 'or'.
auto TryFactorSelectOrEarly = [&](Value *SelOp,
Value *OtherOp) -> Instruction * {
auto *SI = dyn_cast<SelectInst>(SelOp);
if (!SI)
return nullptr;

Value *Cond = SI->getCondition();
Value *T = SI->getTrueValue();
Value *F = SI->getFalseValue();
Value *X, *A;

// Match: select Cond, (X|A), X
if (match(T, m_c_Or(m_Value(X), m_Value(A))) && F == X) {
Value *AorB = Builder.CreateOr(A, OtherOp);
Value *InnerSel = Builder.CreateSelect(Cond, AorB, OtherOp);
return BinaryOperator::CreateOr(X, InnerSel);
}
// Match: select Cond, X, (X|A)
if (match(F, m_c_Or(m_Value(X), m_Value(A))) && T == X) {
Value *AorB = Builder.CreateOr(A, OtherOp);
Value *InnerSel = Builder.CreateSelect(Cond, OtherOp, AorB);
return BinaryOperator::CreateOr(X, InnerSel);
}
return nullptr;
};

if (Instruction *R = TryFactorSelectOrEarly(Op0, Op1))
return R;
if (Instruction *R = TryFactorSelectOrEarly(Op1, Op0))
return R;

if (Instruction *FoldedLogic = foldBinOpIntoSelectOrPhi(I))
return FoldedLogic;

Expand Down
33 changes: 33 additions & 0 deletions llvm/test/Transforms/InstCombine/or-select-factor.ll
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@@ -0,0 +1,33 @@
; RUN: opt -passes=instcombine -S < %s | FileCheck %s
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  1. Use update_test_checks.py to generate test files.
  2. Add some negative tests.
  3. Add some multi-use tests.
  4. Do not add the tgt function. It should be generated by the script above.

Please read https://llvm.org/docs/InstCombineContributorGuide.html#tests for more information.


; Fold: (select C, (x | a), x) | b -> x | select C, (a | b), b

define i8 @src(i8 %x, i8 %y) {
; CHECK-LABEL: @src(
; CHECK-NEXT: [[V0:%.*]] = icmp eq i8 [[Y:%.*]], -1
; CHECK-NEXT: [[V1:%.*]] = or i8 [[X:%.*]], 4
; CHECK-NEXT: [[V2:%.*]] = select i1 [[V0]], i8 [[V1]], i8 [[X]]
; CHECK-NEXT: [[V3:%.*]] = or i8 [[V2]], 1
; CHECK-NEXT: ret i8 [[V3]]
;
%v0 = icmp eq i8 %y, -1
%v1 = or i8 %x, 4
%v2 = select i1 %v0, i8 %v1, i8 %x
%v3 = or i8 %v2, 1
ret i8 %v3
}

define i8 @tgt(i8 %x, i8 %y) {
; CHECK-LABEL: @tgt(
; CHECK-NEXT: [[V0:%.*]] = icmp eq i8 [[Y:%.*]], -1
; CHECK-NEXT: [[V1:%.*]] = select i1 [[V0]], i8 5, i8 1
; CHECK-NEXT: [[V2:%.*]] = or i8 [[X:%.*]], [[V1]]
; CHECK-NEXT: ret i8 [[V2]]
;
%v0 = icmp eq i8 %y, -1
%v1 = select i1 %v0, i8 5, i8 1
%v2 = or i8 %x, %v1
ret i8 %v2
}


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