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[InstCombine] matchThreeWayIntCompare(): commutativity awareness
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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
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@LebedevRI
LebedevRI committed Aug 24, 2019
1 parent 2c75fe7 commit de19f74
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55 changes: 42 additions & 13 deletions llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
View file
Expand Up @@ -2562,20 +2562,49 @@ bool InstCombiner::matchThreeWayIntCompare(SelectInst *SI, Value *&LHS,
// 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);
}
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 false;
return PredB == ICmpInst::ICMP_SLT && RHS == RHS2;
}

Instruction *InstCombiner::foldICmpSelectConstant(ICmpInst &Cmp,
Expand Down
76 changes: 24 additions & 52 deletions llvm/test/Transforms/InstCombine/unrecognized_three-way-comparison.ll
View file
Expand Up @@ -36,14 +36,10 @@ exit:
define i32 @compare_against_zero(i32 %x) {
; CHECK-LABEL: @compare_against_zero(
; CHECK-NEXT: entry:
; CHECK-NEXT: [[CMP1:%.*]] = icmp eq i32 [[X:%.*]], 0
; CHECK-NEXT: [[CMP2_INV:%.*]] = icmp sgt i32 [[X]], -1
; CHECK-NEXT: [[SELECT1:%.*]] = select i1 [[CMP2_INV]], i32 1, i32 -1
; CHECK-NEXT: [[SELECT2:%.*]] = select i1 [[CMP1]], i32 0, i32 [[SELECT1]]
; CHECK-NEXT: [[COND:%.*]] = icmp sgt i32 [[SELECT2]], 0
; CHECK-NEXT: br i1 [[COND]], label [[CALLFOO:%.*]], label [[EXIT:%.*]]
; CHECK-NEXT: [[TMP0:%.*]] = icmp sgt i32 [[X:%.*]], 0
; CHECK-NEXT: br i1 [[TMP0]], label [[CALLFOO:%.*]], label [[EXIT:%.*]]
; CHECK: callfoo:
; CHECK-NEXT: call void @foo(i32 [[SELECT2]])
; CHECK-NEXT: call void @foo(i32 1)
; CHECK-NEXT: br label [[EXIT]]
; CHECK: exit:
; CHECK-NEXT: ret i32 42
Expand Down Expand Up @@ -96,14 +92,10 @@ exit:
define i32 @compare_against_two(i32 %x) {
; CHECK-LABEL: @compare_against_two(
; CHECK-NEXT: entry:
; CHECK-NEXT: [[CMP1:%.*]] = icmp eq i32 [[X:%.*]], 2
; CHECK-NEXT: [[CMP2_INV:%.*]] = icmp sgt i32 [[X]], 1
; CHECK-NEXT: [[SELECT1:%.*]] = select i1 [[CMP2_INV]], i32 1, i32 -1
; CHECK-NEXT: [[SELECT2:%.*]] = select i1 [[CMP1]], i32 0, i32 [[SELECT1]]
; CHECK-NEXT: [[COND:%.*]] = icmp sgt i32 [[SELECT2]], 0
; CHECK-NEXT: br i1 [[COND]], label [[CALLFOO:%.*]], label [[EXIT:%.*]]
; CHECK-NEXT: [[TMP0:%.*]] = icmp sgt i32 [[X:%.*]], 2
; CHECK-NEXT: br i1 [[TMP0]], label [[CALLFOO:%.*]], label [[EXIT:%.*]]
; CHECK: callfoo:
; CHECK-NEXT: call void @foo(i32 [[SELECT2]])
; CHECK-NEXT: call void @foo(i32 1)
; CHECK-NEXT: br label [[EXIT]]
; CHECK: exit:
; CHECK-NEXT: ret i32 42
Expand Down Expand Up @@ -497,13 +489,10 @@ define i32 @compare_against_fortytwo_commutatibility_1(i32 %x) {
; CHECK-NEXT: entry:
; CHECK-NEXT: [[CMP1:%.*]] = icmp ne i32 [[X:%.*]], 42
; CHECK-NEXT: call void @use1(i1 [[CMP1]])
; CHECK-NEXT: [[CMP2:%.*]] = icmp slt i32 [[X]], 42
; CHECK-NEXT: [[SELECT1:%.*]] = select i1 [[CMP2]], i32 -1, i32 1
; CHECK-NEXT: [[SELECT2:%.*]] = select i1 [[CMP1]], i32 [[SELECT1]], i32 0
; CHECK-NEXT: [[COND:%.*]] = icmp sgt i32 [[SELECT2]], 0
; CHECK-NEXT: br i1 [[COND]], label [[CALLFOO:%.*]], label [[EXIT:%.*]]
; CHECK-NEXT: [[TMP0:%.*]] = icmp sgt i32 [[X]], 42
; CHECK-NEXT: br i1 [[TMP0]], label [[CALLFOO:%.*]], label [[EXIT:%.*]]
; CHECK: callfoo:
; CHECK-NEXT: call void @foo(i32 [[SELECT2]])
; CHECK-NEXT: call void @foo(i32 1)
; CHECK-NEXT: br label [[EXIT]]
; CHECK: exit:
; CHECK-NEXT: ret i32 84
Expand All @@ -527,14 +516,10 @@ exit:
define i32 @compare_against_fortytwo_commutatibility_2(i32 %x) {
; CHECK-LABEL: @compare_against_fortytwo_commutatibility_2(
; CHECK-NEXT: entry:
; CHECK-NEXT: [[CMP1:%.*]] = icmp eq i32 [[X:%.*]], 42
; CHECK-NEXT: [[CMP2:%.*]] = icmp sgt i32 [[X]], 41
; CHECK-NEXT: [[SELECT1:%.*]] = select i1 [[CMP2]], i32 1, i32 -1
; CHECK-NEXT: [[SELECT2:%.*]] = select i1 [[CMP1]], i32 0, i32 [[SELECT1]]
; CHECK-NEXT: [[COND:%.*]] = icmp sgt i32 [[SELECT2]], 0
; CHECK-NEXT: br i1 [[COND]], label [[CALLFOO:%.*]], label [[EXIT:%.*]]
; CHECK-NEXT: [[TMP0:%.*]] = icmp sgt i32 [[X:%.*]], 42
; CHECK-NEXT: br i1 [[TMP0]], label [[CALLFOO:%.*]], label [[EXIT:%.*]]
; CHECK: callfoo:
; CHECK-NEXT: call void @foo(i32 [[SELECT2]])
; CHECK-NEXT: call void @foo(i32 1)
; CHECK-NEXT: br label [[EXIT]]
; CHECK: exit:
; CHECK-NEXT: ret i32 84
Expand All @@ -559,13 +544,10 @@ define i32 @compare_against_fortytwo_commutatibility_3(i32 %x) {
; CHECK-NEXT: entry:
; CHECK-NEXT: [[CMP1:%.*]] = icmp ne i32 [[X:%.*]], 42
; CHECK-NEXT: call void @use1(i1 [[CMP1]])
; CHECK-NEXT: [[CMP2:%.*]] = icmp sgt i32 [[X]], 41
; CHECK-NEXT: [[SELECT1:%.*]] = select i1 [[CMP2]], i32 1, i32 -1
; CHECK-NEXT: [[SELECT2:%.*]] = select i1 [[CMP1]], i32 [[SELECT1]], i32 0
; CHECK-NEXT: [[COND:%.*]] = icmp sgt i32 [[SELECT2]], 0
; CHECK-NEXT: br i1 [[COND]], label [[CALLFOO:%.*]], label [[EXIT:%.*]]
; CHECK-NEXT: [[TMP0:%.*]] = icmp sgt i32 [[X]], 42
; CHECK-NEXT: br i1 [[TMP0]], label [[CALLFOO:%.*]], label [[EXIT:%.*]]
; CHECK: callfoo:
; CHECK-NEXT: call void @foo(i32 [[SELECT2]])
; CHECK-NEXT: call void @foo(i32 1)
; CHECK-NEXT: br label [[EXIT]]
; CHECK: exit:
; CHECK-NEXT: ret i32 84
Expand Down Expand Up @@ -616,14 +598,10 @@ exit:
define i32 @compare_against_arbitrary_value_commutativity1(i32 %x, i32 %c) {
; CHECK-LABEL: @compare_against_arbitrary_value_commutativity1(
; CHECK-NEXT: entry:
; CHECK-NEXT: [[CMP1:%.*]] = icmp eq i32 [[X:%.*]], [[C:%.*]]
; CHECK-NEXT: [[CMP2:%.*]] = icmp sgt i32 [[C]], [[X]]
; CHECK-NEXT: [[SELECT1:%.*]] = select i1 [[CMP2]], i32 -1, i32 1
; CHECK-NEXT: [[SELECT2:%.*]] = select i1 [[CMP1]], i32 0, i32 [[SELECT1]]
; CHECK-NEXT: [[COND:%.*]] = icmp sgt i32 [[SELECT2]], 0
; CHECK-NEXT: br i1 [[COND]], label [[CALLFOO:%.*]], label [[EXIT:%.*]]
; CHECK-NEXT: [[TMP0:%.*]] = icmp sgt i32 [[X:%.*]], [[C:%.*]]
; CHECK-NEXT: br i1 [[TMP0]], label [[CALLFOO:%.*]], label [[EXIT:%.*]]
; CHECK: callfoo:
; CHECK-NEXT: call void @foo(i32 [[SELECT2]])
; CHECK-NEXT: call void @foo(i32 1)
; CHECK-NEXT: br label [[EXIT]]
; CHECK: exit:
; CHECK-NEXT: ret i32 42
Expand All @@ -648,13 +626,10 @@ define i32 @compare_against_arbitrary_value_commutativity2(i32 %x, i32 %c) {
; CHECK-NEXT: entry:
; CHECK-NEXT: [[CMP1:%.*]] = icmp ne i32 [[X:%.*]], [[C:%.*]]
; CHECK-NEXT: call void @use1(i1 [[CMP1]])
; CHECK-NEXT: [[CMP2:%.*]] = icmp slt i32 [[X]], [[C]]
; CHECK-NEXT: [[SELECT1:%.*]] = select i1 [[CMP2]], i32 -1, i32 1
; CHECK-NEXT: [[SELECT2:%.*]] = select i1 [[CMP1]], i32 [[SELECT1]], i32 0
; CHECK-NEXT: [[COND:%.*]] = icmp sgt i32 [[SELECT2]], 0
; CHECK-NEXT: br i1 [[COND]], label [[CALLFOO:%.*]], label [[EXIT:%.*]]
; CHECK-NEXT: [[TMP0:%.*]] = icmp sgt i32 [[X]], [[C]]
; CHECK-NEXT: br i1 [[TMP0]], label [[CALLFOO:%.*]], label [[EXIT:%.*]]
; CHECK: callfoo:
; CHECK-NEXT: call void @foo(i32 [[SELECT2]])
; CHECK-NEXT: call void @foo(i32 1)
; CHECK-NEXT: br label [[EXIT]]
; CHECK: exit:
; CHECK-NEXT: ret i32 42
Expand All @@ -680,13 +655,10 @@ define i32 @compare_against_arbitrary_value_commutativity3(i32 %x, i32 %c) {
; CHECK-NEXT: entry:
; CHECK-NEXT: [[CMP1:%.*]] = icmp ne i32 [[X:%.*]], [[C:%.*]]
; CHECK-NEXT: call void @use1(i1 [[CMP1]])
; CHECK-NEXT: [[CMP2:%.*]] = icmp sgt i32 [[C]], [[X]]
; CHECK-NEXT: [[SELECT1:%.*]] = select i1 [[CMP2]], i32 -1, i32 1
; CHECK-NEXT: [[SELECT2:%.*]] = select i1 [[CMP1]], i32 [[SELECT1]], i32 0
; CHECK-NEXT: [[COND:%.*]] = icmp sgt i32 [[SELECT2]], 0
; CHECK-NEXT: br i1 [[COND]], label [[CALLFOO:%.*]], label [[EXIT:%.*]]
; CHECK-NEXT: [[TMP0:%.*]] = icmp sgt i32 [[X]], [[C]]
; CHECK-NEXT: br i1 [[TMP0]], label [[CALLFOO:%.*]], label [[EXIT:%.*]]
; CHECK: callfoo:
; CHECK-NEXT: call void @foo(i32 [[SELECT2]])
; CHECK-NEXT: call void @foo(i32 1)
; CHECK-NEXT: br label [[EXIT]]
; CHECK: exit:
; CHECK-NEXT: ret i32 42
Expand Down

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