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[InstCombine] adjust branch on logical-and fold

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The transform was just added with:
115d2f69a5
...but as noted in post-commit feedback, it was
confusingly coded. Now, we create the final
expected canonicalized form directly and put
an extra use check on the match, so we should
not ever end up with more instructions.
This commit is contained in:
Sanjay Patel
2022-10-31 17:32:34 -04:00
parent aa887ff3f4
commit 1f8ac37e2d
2 changed files with 12 additions and 7 deletions
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12
llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
View File

@@ -3187,13 +3187,17 @@ Instruction *InstCombinerImpl::visitBranchInst(BranchInst &BI) {
return replaceOperand(BI, 0, X);
}
// br (X && !Y), T, F --> br ((X && Y) || !X), F, T
// Canonicalize logical-and-with-invert as logical-or-with-invert.
// This is done by inverting the condition and swapping successors:
// br (X && !Y), T, F --> br !(X && !Y), F, T --> br (!X || Y), F, T
Value *Y;
if (isa<SelectInst>(Cond) &&
match(Cond, m_OneUse(m_LogicalAnd(m_Value(X), m_Not(m_Value(Y)))))) {
Value *AndOr = Builder.CreateSelect(X, Y, Builder.getTrue());
match(Cond,
m_OneUse(m_LogicalAnd(m_Value(X), m_OneUse(m_Not(m_Value(Y))))))) {
Value *NotX = Builder.CreateNot(X, "not." + X->getName());
Value *Or = Builder.CreateLogicalOr(NotX, Y);
BI.swapSuccessors();
return replaceOperand(BI, 0, AndOr);
return replaceOperand(BI, 0, Or);
}
// If the condition is irrelevant, remove the use so that other

7
llvm/test/Transforms/InstCombine/branch.ll
View File

@@ -189,14 +189,15 @@ f:
ret i32 3
}
; negative test
define i32 @logical_and_not_use1(i1 %x, i1 %y) {
; CHECK-LABEL: @logical_and_not_use1(
; CHECK-NEXT: entry:
; CHECK-NEXT: [[NOTY:%.*]] = xor i1 [[Y:%.*]], true
; CHECK-NEXT: call void @use(i1 [[NOTY]])
; CHECK-NEXT: [[NOT_X:%.*]] = xor i1 [[X:%.*]], true
; CHECK-NEXT: [[TMP0:%.*]] = select i1 [[NOT_X]], i1 true, i1 [[Y]]
; CHECK-NEXT: br i1 [[TMP0]], label [[F:%.*]], label [[T:%.*]]
; CHECK-NEXT: [[AND:%.*]] = select i1 [[X:%.*]], i1 [[NOTY]], i1 false
; CHECK-NEXT: br i1 [[AND]], label [[T:%.*]], label [[F:%.*]]
; CHECK: t:
; CHECK-NEXT: ret i32 42
; CHECK: f: