[InstCombine] matchThreeWayIntCompare(): commutativity awareness
Summary:
`matchThreeWayIntCompare()` looks for
```
select i1 (a == b),
i32 Equal,
i32 (select i1 (a < b), i32 Less, i32 Greater)
```
but both of these selects/compares can be in it's commuted form,
so out of 8 variants, only the two most basic ones is handled.
This fixes regression being introduced in D66232.
Reviewers: spatel, nikic, efriedma, xbolva00
Reviewed By: spatel
Subscribers: hiraditya, llvm-commits
Tags: #llvm
Differential Revision: https://reviews.llvm.org/D66607
llvm-svn: 369841
diff --git a/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp b/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
index 0b3eddd..b80e9ad 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
@@ -2562,20 +2562,49 @@
// TODO: Generalize this to work with other comparison idioms or ensure
// they get canonicalized into this form.
- // select i1 (a == b), i32 Equal, i32 (select i1 (a < b), i32 Less, i32
- // Greater), where Equal, Less and Greater are placeholders for any three
- // constants.
- ICmpInst::Predicate PredA, PredB;
- if (match(SI->getTrueValue(), m_ConstantInt(Equal)) &&
- match(SI->getCondition(), m_ICmp(PredA, m_Value(LHS), m_Value(RHS))) &&
- PredA == ICmpInst::ICMP_EQ &&
- match(SI->getFalseValue(),
- m_Select(m_ICmp(PredB, m_Specific(LHS), m_Specific(RHS)),
- m_ConstantInt(Less), m_ConstantInt(Greater))) &&
- PredB == ICmpInst::ICMP_SLT) {
- return true;
+ // select i1 (a == b),
+ // i32 Equal,
+ // i32 (select i1 (a < b), i32 Less, i32 Greater)
+ // where Equal, Less and Greater are placeholders for any three constants.
+ ICmpInst::Predicate PredA;
+ if (!match(SI->getCondition(), m_ICmp(PredA, m_Value(LHS), m_Value(RHS))) ||
+ !ICmpInst::isEquality(PredA))
+ return false;
+ Value *EqualVal = SI->getTrueValue();
+ Value *UnequalVal = SI->getFalseValue();
+ // We still can get non-canonical predicate here, so canonicalize.
+ if (PredA == ICmpInst::ICMP_NE)
+ std::swap(EqualVal, UnequalVal);
+ if (!match(EqualVal, m_ConstantInt(Equal)))
+ return false;
+ ICmpInst::Predicate PredB;
+ Value *LHS2, *RHS2;
+ if (!match(UnequalVal, m_Select(m_ICmp(PredB, m_Value(LHS2), m_Value(RHS2)),
+ m_ConstantInt(Less), m_ConstantInt(Greater))))
+ return false;
+ // We can get predicate mismatch here, so canonicalize if possible:
+ // First, ensure that 'LHS' match.
+ if (LHS2 != LHS) {
+ // x sgt y <--> y slt x
+ std::swap(LHS2, RHS2);
+ PredB = ICmpInst::getSwappedPredicate(PredB);
}
- return false;
+ if (LHS2 != LHS)
+ return false;
+ // We also need to canonicalize 'RHS'.
+ if (PredB == ICmpInst::ICMP_SGT && isa<Constant>(RHS2)) {
+ // x sgt C-1 <--> x sge C <--> not(x slt C)
+ auto FlippedStrictness =
+ getFlippedStrictnessPredicateAndConstant(PredB, cast<Constant>(RHS2));
+ if (!FlippedStrictness)
+ return false;
+ assert(FlippedStrictness->first == ICmpInst::ICMP_SGE && "Sanity check");
+ RHS2 = FlippedStrictness->second;
+ // And kind-of perform the result swap.
+ std::swap(Less, Greater);
+ PredB = ICmpInst::ICMP_SLT;
+ }
+ return PredB == ICmpInst::ICMP_SLT && RHS == RHS2;
}
Instruction *InstCombiner::foldICmpSelectConstant(ICmpInst &Cmp,