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[LoopUnswitch] Simplify branch condition if it is select with constant operands

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This fixes the miscompilation reported in https://reviews.llvm.org/rG5bb38e84d3d0#986154 .

`select _, true, false` matches both m_LogicalAnd and m_LogicalOr, making later
transformations confused.
Simplify the branch condition to not have the form.
This commit is contained in:
Juneyoung Lee 2021-03-30 20:03:50 +09:00
parent 6da35d08b6
commit bb16c311ef
2 changed files with 9 additions and 2 deletions
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7
lib/Transforms/Scalar/SimpleLoopUnswitch.cpp
View File

@ -2645,6 +2645,13 @@ unswitchBestCondition(Loop &L, DominatorTree &DT, LoopInfo &LI,
BI->getSuccessor(0) == BI->getSuccessor(1))
continue;
// If BI's condition is 'select _, true, false', simplify it to confuse
// matchers
Value *Cond = BI->getCondition(), *CondNext;
while (match(Cond, m_Select(m_Value(CondNext), m_One(), m_Zero())))
Cond = CondNext;
BI->setCondition(Cond);
if (L.isLoopInvariant(BI->getCondition())) {
UnswitchCandidates.push_back({BI, {BI->getCondition()}});
continue;

4
test/Transforms/SimpleLoopUnswitch/nontrivial-unswitch.ll
View File

@ -4248,7 +4248,7 @@ loop_begin:
; CHECK-NEXT: %[[V2:.*]] = load i1, i1* %ptr2
; CHECK-NEXT: %[[AND1:.*]] = select i1 %[[V1]], i1 true, i1 false
; CHECK-NEXT: %[[AND2:.*]] = select i1 %[[AND1]], i1 true, i1 false
; CHECK-NEXT: br i1 %[[AND2]], label %loop_a, label %loop_b
; CHECK-NEXT: br i1 %[[V1]], label %loop_a, label %loop_b
loop_a:
call i32 @a()
@ -4326,7 +4326,7 @@ loop_begin:
; CHECK-NEXT: %[[V2:.*]] = load i1, i1* %ptr2
; CHECK-NEXT: %[[AND1:.*]] = select i1 %[[V1]], i1 true, i1 false
; CHECK-NEXT: %[[AND2:.*]] = select i1 %[[AND1]], i1 true, i1 false
; CHECK-NEXT: br i1 %[[AND2]], label %loop_b, label %loop_a
; CHECK-NEXT: br i1 %[[V1]], label %loop_b, label %loop_a
loop_a:
call i32 @a()