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[InstCombine] Fold (X==Z) ? (Y==Z) : (!(Y==Z) && X==Y) --> X==Y (#108619
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This corresponds to the canonicalized form of some logic that was
seen in Swift-generated code for comparing optional pointers:
`(X==Z || Y==Z) ? (X==Z && Y==Z) : X==Y --> X==Y`
where `Z` was the constant `0`.

https://alive2.llvm.org/ce/z/J_3aa9
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@citymarina
citymarina authored Oct 3, 2024
1 parent ee4dd14 commit d0d12fc
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1 change: 1 addition & 0 deletions llvm/lib/Transforms/InstCombine/InstCombineInternal.h
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Expand Up @@ -739,6 +739,7 @@ class LLVM_LIBRARY_VISIBILITY InstCombinerImpl final
Instruction *foldSelectOfBools(SelectInst &SI);
Instruction *foldSelectToCmp(SelectInst &SI);
Instruction *foldSelectExtConst(SelectInst &Sel);
Instruction *foldSelectEqualityTest(SelectInst &SI);
Instruction *foldSelectOpOp(SelectInst &SI, Instruction *TI, Instruction *FI);
Instruction *foldSelectIntoOp(SelectInst &SI, Value *, Value *);
Instruction *foldSPFofSPF(Instruction *Inner, SelectPatternFlavor SPF1,
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41 changes: 41 additions & 0 deletions llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
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Expand Up @@ -1410,6 +1410,44 @@ Instruction *InstCombinerImpl::foldSelectValueEquivalence(SelectInst &Sel,
return nullptr;
}

/// Fold the following code sequence:
/// \code
/// %XeqZ = icmp eq i64 %X, %Z
/// %YeqZ = icmp eq i64 %Y, %Z
/// %XeqY = icmp eq i64 %X, %Y
/// %not.YeqZ = xor i1 %YeqZ, true
/// %and = select i1 %not.YeqZ, i1 %XeqY, i1 false
/// %equal = select i1 %XeqZ, i1 %YeqZ, i1 %and
/// \code
///
/// into:
/// %equal = icmp eq i64 %X, %Y
Instruction *InstCombinerImpl::foldSelectEqualityTest(SelectInst &Sel) {
Value *X, *Y, *Z;
Value *XeqY, *XeqZ = Sel.getCondition(), *YeqZ = Sel.getTrueValue();

if (!match(XeqZ, m_SpecificICmp(ICmpInst::ICMP_EQ, m_Value(X), m_Value(Z))))
return nullptr;

if (!match(YeqZ,
m_c_SpecificICmp(ICmpInst::ICMP_EQ, m_Value(Y), m_Specific(Z))))
std::swap(X, Z);

if (!match(YeqZ,
m_c_SpecificICmp(ICmpInst::ICMP_EQ, m_Value(Y), m_Specific(Z))))
return nullptr;

if (!match(Sel.getFalseValue(),
m_c_LogicalAnd(m_Not(m_Specific(YeqZ)), m_Value(XeqY))))
return nullptr;

if (!match(XeqY,
m_c_SpecificICmp(ICmpInst::ICMP_EQ, m_Specific(X), m_Specific(Y))))
return nullptr;

return replaceInstUsesWith(Sel, XeqY);
}

// See if this is a pattern like:
// %old_cmp1 = icmp slt i32 %x, C2
// %old_replacement = select i1 %old_cmp1, i32 %target_low, i32 %target_high
Expand Down Expand Up @@ -4112,6 +4150,9 @@ Instruction *InstCombinerImpl::visitSelectInst(SelectInst &SI) {
if (Instruction *I = foldSelectToCmp(SI))
return I;

if (Instruction *I = foldSelectEqualityTest(SI))
return I;

// Fold:
// (select A && B, T, F) -> (select A, (select B, T, F), F)
// (select A || B, T, F) -> (select A, T, (select B, T, F))
Expand Down
229 changes: 229 additions & 0 deletions llvm/test/Transforms/InstCombine/icmp-equality-test.ll
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@@ -0,0 +1,229 @@
; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
; RUN: opt < %s -passes=instcombine -S | FileCheck %s

define i1 @icmp_equality_test(i64 %X, i64 %Y, i64 %Z) {
; CHECK-LABEL: @icmp_equality_test(
; CHECK-NEXT: entry:
; CHECK-NEXT: [[XEQY:%.*]] = icmp eq i64 [[X:%.*]], [[Y:%.*]]
; CHECK-NEXT: ret i1 [[XEQY]]
;
entry:
%XeqZ = icmp eq i64 %X, %Z
%YeqZ = icmp eq i64 %Y, %Z
%XeqY = icmp eq i64 %X, %Y
%not.YeqZ = xor i1 %YeqZ, true
%and = select i1 %not.YeqZ, i1 %XeqY, i1 false
%equal = select i1 %XeqZ, i1 %YeqZ, i1 %and
ret i1 %equal
}

define i1 @icmp_equality_test_constant(i42 %X, i42 %Y) {
; CHECK-LABEL: @icmp_equality_test_constant(
; CHECK-NEXT: entry:
; CHECK-NEXT: [[XEQY:%.*]] = icmp eq i42 [[X:%.*]], [[Y:%.*]]
; CHECK-NEXT: ret i1 [[XEQY]]
;
entry:
%XeqC = icmp eq i42 %X, -42
%YeqC = icmp eq i42 %Y, -42
%XeqY = icmp eq i42 %X, %Y
%not.YeqC = xor i1 %YeqC, true
%and = select i1 %not.YeqC, i1 %XeqY, i1 false
%equal = select i1 %XeqC, i1 %YeqC, i1 %and
ret i1 %equal
}

define i1 @icmp_equality_test_swift_optional_pointers(i64 %X, i64 %Y) {
; CHECK-LABEL: @icmp_equality_test_swift_optional_pointers(
; CHECK-NEXT: entry:
; CHECK-NEXT: [[XEQY:%.*]] = icmp eq i64 [[X:%.*]], [[Y:%.*]]
; CHECK-NEXT: ret i1 [[XEQY]]
;
entry:
%XeqC = icmp eq i64 %X, 0
%YeqC = icmp eq i64 %Y, 0
%either = select i1 %XeqC, i1 true, i1 %YeqC
%both = select i1 %XeqC, i1 %YeqC, i1 false
%XeqY = icmp eq i64 %X, %Y
%equal = select i1 %either, i1 %both, i1 %XeqY
ret i1 %equal
}

define <2 x i1> @icmp_equality_test_vector(<2 x i64> %X, <2 x i64> %Y) {
; CHECK-LABEL: @icmp_equality_test_vector(
; CHECK-NEXT: entry:
; CHECK-NEXT: [[XEQY:%.*]] = icmp eq <2 x i64> [[X:%.*]], [[Y:%.*]]
; CHECK-NEXT: ret <2 x i1> [[XEQY]]
;
entry:
%XeqC = icmp eq <2 x i64> %X, <i64 123, i64 456>
%YeqC = icmp eq <2 x i64> %Y, <i64 123, i64 456>
%XeqY = icmp eq <2 x i64> %X, %Y
%not.YeqC = xor <2 x i1> %YeqC, <i1 true, i1 true>
%and = select <2 x i1> %not.YeqC, <2 x i1> %XeqY, <2 x i1> <i1 false, i1 false>
%equal = select <2 x i1> %XeqC, <2 x i1> %YeqC, <2 x i1> %and
ret <2 x i1> %equal
}

define i1 @icmp_equality_test_commute_icmp1(i64 %X, i64 %Y, i64 %Z) {
; CHECK-LABEL: @icmp_equality_test_commute_icmp1(
; CHECK-NEXT: entry:
; CHECK-NEXT: [[XEQY:%.*]] = icmp eq i64 [[Y:%.*]], [[X:%.*]]
; CHECK-NEXT: ret i1 [[XEQY]]
;
entry:
%XeqZ = icmp eq i64 %Z, %X
%YeqZ = icmp eq i64 %Z, %Y
%XeqY = icmp eq i64 %Y, %X
%not.YeqZ = xor i1 %YeqZ, true
%and = select i1 %not.YeqZ, i1 %XeqY, i1 false
%equal = select i1 %XeqZ, i1 %YeqZ, i1 %and
ret i1 %equal
}

define i1 @icmp_equality_test_commute_icmp2(i64 %X, i64 %Y, i64 %Z) {
; CHECK-LABEL: @icmp_equality_test_commute_icmp2(
; CHECK-NEXT: [[XEQY:%.*]] = icmp eq i64 [[Y:%.*]], [[X:%.*]]
; CHECK-NEXT: ret i1 [[XEQY]]
;
%XeqZ = icmp eq i64 %Z, %X
%YeqZ = icmp eq i64 %Y, %Z
%XeqY = icmp eq i64 %Y, %X
%not.YeqZ = xor i1 %YeqZ, true
%and = select i1 %not.YeqZ, i1 %XeqY, i1 false
%equal = select i1 %XeqZ, i1 %YeqZ, i1 %and
ret i1 %equal
}

define i1 @icmp_equality_test_commute_select1(i64 %X, i64 %Y, i64 %Z) {
; CHECK-LABEL: @icmp_equality_test_commute_select1(
; CHECK-NEXT: entry:
; CHECK-NEXT: [[XEQY:%.*]] = icmp eq i64 [[X:%.*]], [[Y:%.*]]
; CHECK-NEXT: ret i1 [[XEQY]]
;
entry:
%XeqZ = icmp eq i64 %X, %Z
%YeqZ = icmp eq i64 %Y, %Z
%XeqY = icmp eq i64 %X, %Y
%and = select i1 %YeqZ, i1 false, i1 %XeqY
%equal = select i1 %XeqZ, i1 %YeqZ, i1 %and
ret i1 %equal
}

define i1 @icmp_equality_test_commute_select2(i64 %X, i64 %Y, i64 %Z) {
; CHECK-LABEL: @icmp_equality_test_commute_select2(
; CHECK-NEXT: entry:
; CHECK-NEXT: [[XEQY:%.*]] = icmp eq i64 [[X:%.*]], [[Y:%.*]]
; CHECK-NEXT: ret i1 [[XEQY]]
;
entry:
%XeqZ = icmp eq i64 %X, %Z
%YeqZ = icmp eq i64 %Y, %Z
%XeqY = icmp eq i64 %X, %Y
%not.XeqZ = xor i1 %XeqZ, true
%and = select i1 %YeqZ, i1 false, i1 %XeqY
%equal = select i1 %not.XeqZ, i1 %and, i1 %YeqZ
ret i1 %equal
}

; Negative tests below

define i1 @icmp_equality_test_wrong_constant(i64 %X, i64 %Y) {
; CHECK-LABEL: @icmp_equality_test_wrong_constant(
; CHECK-NEXT: entry:
; CHECK-NEXT: [[XEQC:%.*]] = icmp eq i64 [[X:%.*]], 0
; CHECK-NEXT: [[YEQC:%.*]] = icmp eq i64 [[Y:%.*]], 999
; CHECK-NEXT: [[XEQY:%.*]] = icmp eq i64 [[X]], [[Y]]
; CHECK-NEXT: [[NOT_YEQC:%.*]] = xor i1 [[YEQC]], true
; CHECK-NEXT: [[AND:%.*]] = select i1 [[NOT_YEQC]], i1 [[XEQY]], i1 false
; CHECK-NEXT: [[EQUAL:%.*]] = select i1 [[XEQC]], i1 [[YEQC]], i1 [[AND]]
; CHECK-NEXT: ret i1 [[EQUAL]]
;
entry:
%XeqC = icmp eq i64 %X, 0
%YeqC = icmp eq i64 %Y, 999
%XeqY = icmp eq i64 %X, %Y
%not.YeqC = xor i1 %YeqC, true
%and = select i1 %not.YeqC, i1 %XeqY, i1 false
%equal = select i1 %XeqC, i1 %YeqC, i1 %and
ret i1 %equal
}

define i1 @icmp_equality_test_missing_not(i64 %X, i64 %Y, i64 %Z) {
; CHECK-LABEL: @icmp_equality_test_missing_not(
; CHECK-NEXT: [[XEQZ:%.*]] = icmp eq i64 [[X:%.*]], [[Z:%.*]]
; CHECK-NEXT: [[YEQZ:%.*]] = icmp eq i64 [[Y:%.*]], [[Z]]
; CHECK-NEXT: [[XEQY:%.*]] = icmp eq i64 [[X]], [[Y]]
; CHECK-NEXT: [[AND:%.*]] = select i1 [[YEQZ]], i1 [[XEQY]], i1 false
; CHECK-NEXT: [[EQUAL:%.*]] = select i1 [[XEQZ]], i1 [[YEQZ]], i1 [[AND]]
; CHECK-NEXT: ret i1 [[EQUAL]]
;
%XeqZ = icmp eq i64 %X, %Z
%YeqZ = icmp eq i64 %Y, %Z
%XeqY = icmp eq i64 %X, %Y
%and = select i1 %YeqZ, i1 %XeqY, i1 false
%equal = select i1 %XeqZ, i1 %YeqZ, i1 %and
ret i1 %equal
}

define i1 @icmp_equality_test_wrong_and(i64 %X, i64 %Y, i64 %Z) {
; CHECK-LABEL: @icmp_equality_test_wrong_and(
; CHECK-NEXT: entry:
; CHECK-NEXT: [[XEQZ:%.*]] = icmp eq i64 [[X:%.*]], [[Z:%.*]]
; CHECK-NEXT: [[YEQZ:%.*]] = icmp eq i64 [[Y:%.*]], [[Z]]
; CHECK-NEXT: [[XEQY:%.*]] = icmp eq i64 [[X]], [[Y]]
; CHECK-NEXT: [[AND:%.*]] = select i1 [[YEQZ]], i1 [[XEQY]], i1 false
; CHECK-NEXT: [[EQUAL:%.*]] = select i1 [[XEQZ]], i1 [[YEQZ]], i1 [[AND]]
; CHECK-NEXT: ret i1 [[EQUAL]]
;
entry:
%XeqZ = icmp eq i64 %X, %Z
%YeqZ = icmp eq i64 %Y, %Z
%XeqY = icmp eq i64 %X, %Y
%not.YeqZ = xor i1 %YeqZ, true
%and = select i1 %not.YeqZ, i1 false, i1 %XeqY
%equal = select i1 %XeqZ, i1 %YeqZ, i1 %and
ret i1 %equal
}

define i1 @icmp_equality_test_wrong_cmp(i64 %X, i64 %Y, i64 %Z) {
; CHECK-LABEL: @icmp_equality_test_wrong_cmp(
; CHECK-NEXT: entry:
; CHECK-NEXT: [[XEQZ:%.*]] = icmp eq i64 [[X:%.*]], [[Z:%.*]]
; CHECK-NEXT: [[YEQZ:%.*]] = icmp eq i64 [[Y:%.*]], [[Z]]
; CHECK-NEXT: [[XEQY:%.*]] = icmp eq i64 [[X]], 999
; CHECK-NEXT: [[NOT_YEQZ:%.*]] = xor i1 [[YEQZ]], true
; CHECK-NEXT: [[AND:%.*]] = select i1 [[NOT_YEQZ]], i1 [[XEQY]], i1 false
; CHECK-NEXT: [[EQUAL:%.*]] = select i1 [[XEQZ]], i1 [[YEQZ]], i1 [[AND]]
; CHECK-NEXT: ret i1 [[EQUAL]]
;
entry:
%XeqZ = icmp eq i64 %X, %Z
%YeqZ = icmp eq i64 %Y, %Z
%XeqY = icmp eq i64 %X, 999
%not.YeqZ = xor i1 %YeqZ, true
%and = select i1 %not.YeqZ, i1 %XeqY, i1 false
%equal = select i1 %XeqZ, i1 %YeqZ, i1 %and
ret i1 %equal
}

define i1 @icmp_equality_test_wrong_equal(i64 %X, i64 %Y, i64 %Z) {
; CHECK-LABEL: @icmp_equality_test_wrong_equal(
; CHECK-NEXT: entry:
; CHECK-NEXT: [[XEQZ:%.*]] = icmp eq i64 [[X:%.*]], [[Z:%.*]]
; CHECK-NEXT: [[YEQZ:%.*]] = icmp eq i64 [[Y:%.*]], [[Z]]
; CHECK-NEXT: [[XEQY:%.*]] = icmp eq i64 [[X]], [[Y]]
; CHECK-NEXT: [[NOT_YEQZ:%.*]] = xor i1 [[YEQZ]], true
; CHECK-NEXT: [[AND:%.*]] = select i1 [[NOT_YEQZ]], i1 [[XEQY]], i1 false
; CHECK-NEXT: [[EQUAL:%.*]] = select i1 [[XEQZ]], i1 [[AND]], i1 [[YEQZ]]
; CHECK-NEXT: ret i1 [[EQUAL]]
;
entry:
%XeqZ = icmp eq i64 %X, %Z
%YeqZ = icmp eq i64 %Y, %Z
%XeqY = icmp eq i64 %X, %Y
%not.YeqZ = xor i1 %YeqZ, true
%and = select i1 %not.YeqZ, i1 %XeqY, i1 false
%equal = select i1 %XeqZ, i1 %and, i1 %YeqZ
ret i1 %equal
}

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