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[InstCombine] Fold (X==Z) ? (Y==Z) : (!(Y==Z) && X==Y) --> X==Y (#108619)
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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‎llvm/lib/Transforms/InstCombine/InstCombineInternal.h

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Original file line numberDiff line numberDiff line change
@@ -739,6 +739,7 @@ class LLVM_LIBRARY_VISIBILITY InstCombinerImpl final
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Instruction *foldSelectOfBools(SelectInst &SI);
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Instruction *foldSelectToCmp(SelectInst &SI);
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Instruction *foldSelectExtConst(SelectInst &Sel);
742+
Instruction *foldSelectEqualityTest(SelectInst &SI);
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Instruction *foldSelectOpOp(SelectInst &SI, Instruction *TI, Instruction *FI);
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Instruction *foldSelectIntoOp(SelectInst &SI, Value *, Value *);
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Instruction *foldSPFofSPF(Instruction *Inner, SelectPatternFlavor SPF1,

‎llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp

Lines changed: 41 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -1410,6 +1410,44 @@ Instruction *InstCombinerImpl::foldSelectValueEquivalence(SelectInst &Sel,
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return nullptr;
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}
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/// Fold the following code sequence:
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/// \code
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/// %XeqZ = icmp eq i64 %X, %Z
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/// %YeqZ = icmp eq i64 %Y, %Z
1417+
/// %XeqY = icmp eq i64 %X, %Y
1418+
/// %not.YeqZ = xor i1 %YeqZ, true
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/// %and = select i1 %not.YeqZ, i1 %XeqY, i1 false
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/// %equal = select i1 %XeqZ, i1 %YeqZ, i1 %and
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/// \code
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///
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/// into:
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/// %equal = icmp eq i64 %X, %Y
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Instruction *InstCombinerImpl::foldSelectEqualityTest(SelectInst &Sel) {
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Value *X, *Y, *Z;
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Value *XeqY, *XeqZ = Sel.getCondition(), *YeqZ = Sel.getTrueValue();
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if (!match(XeqZ, m_SpecificICmp(ICmpInst::ICMP_EQ, m_Value(X), m_Value(Z))))
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return nullptr;
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if (!match(YeqZ,
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m_c_SpecificICmp(ICmpInst::ICMP_EQ, m_Value(Y), m_Specific(Z))))
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std::swap(X, Z);
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if (!match(YeqZ,
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m_c_SpecificICmp(ICmpInst::ICMP_EQ, m_Value(Y), m_Specific(Z))))
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return nullptr;
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if (!match(Sel.getFalseValue(),
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m_c_LogicalAnd(m_Not(m_Specific(YeqZ)), m_Value(XeqY))))
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return nullptr;
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if (!match(XeqY,
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m_c_SpecificICmp(ICmpInst::ICMP_EQ, m_Specific(X), m_Specific(Y))))
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return nullptr;
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return replaceInstUsesWith(Sel, XeqY);
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}
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// See if this is a pattern like:
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// %old_cmp1 = icmp slt i32 %x, C2
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// %old_replacement = select i1 %old_cmp1, i32 %target_low, i32 %target_high
@@ -4112,6 +4150,9 @@ Instruction *InstCombinerImpl::visitSelectInst(SelectInst &SI) {
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if (Instruction *I = foldSelectToCmp(SI))
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return I;
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if (Instruction *I = foldSelectEqualityTest(SI))
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return I;
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// Fold:
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// (select A && B, T, F) -> (select A, (select B, T, F), F)
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// (select A || B, T, F) -> (select A, T, (select B, T, F))

‎llvm/test/Transforms/InstCombine/icmp-equality-test.ll

Lines changed: 229 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,229 @@
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; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
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; RUN: opt < %s -passes=instcombine -S | FileCheck %s
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define i1 @icmp_equality_test(i64 %X, i64 %Y, i64 %Z) {
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; CHECK-LABEL: @icmp_equality_test(
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; CHECK-NEXT: entry:
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; CHECK-NEXT: [[XEQY:%.*]] = icmp eq i64 [[X:%.*]], [[Y:%.*]]
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; CHECK-NEXT: ret i1 [[XEQY]]
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;
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entry:
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%XeqZ = icmp eq i64 %X, %Z
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%YeqZ = icmp eq i64 %Y, %Z
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%XeqY = icmp eq i64 %X, %Y
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%not.YeqZ = xor i1 %YeqZ, true
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%and = select i1 %not.YeqZ, i1 %XeqY, i1 false
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%equal = select i1 %XeqZ, i1 %YeqZ, i1 %and
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ret i1 %equal
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}
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define i1 @icmp_equality_test_constant(i42 %X, i42 %Y) {
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; CHECK-LABEL: @icmp_equality_test_constant(
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; CHECK-NEXT: entry:
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; CHECK-NEXT: [[XEQY:%.*]] = icmp eq i42 [[X:%.*]], [[Y:%.*]]
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; CHECK-NEXT: ret i1 [[XEQY]]
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;
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entry:
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%XeqC = icmp eq i42 %X, -42
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%YeqC = icmp eq i42 %Y, -42
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%XeqY = icmp eq i42 %X, %Y
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%not.YeqC = xor i1 %YeqC, true
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%and = select i1 %not.YeqC, i1 %XeqY, i1 false
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%equal = select i1 %XeqC, i1 %YeqC, i1 %and
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ret i1 %equal
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}
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define i1 @icmp_equality_test_swift_optional_pointers(i64 %X, i64 %Y) {
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; CHECK-LABEL: @icmp_equality_test_swift_optional_pointers(
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; CHECK-NEXT: entry:
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; CHECK-NEXT: [[XEQY:%.*]] = icmp eq i64 [[X:%.*]], [[Y:%.*]]
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; CHECK-NEXT: ret i1 [[XEQY]]
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;
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entry:
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%XeqC = icmp eq i64 %X, 0
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%YeqC = icmp eq i64 %Y, 0
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%either = select i1 %XeqC, i1 true, i1 %YeqC
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%both = select i1 %XeqC, i1 %YeqC, i1 false
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%XeqY = icmp eq i64 %X, %Y
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%equal = select i1 %either, i1 %both, i1 %XeqY
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ret i1 %equal
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}
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define <2 x i1> @icmp_equality_test_vector(<2 x i64> %X, <2 x i64> %Y) {
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; CHECK-LABEL: @icmp_equality_test_vector(
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; CHECK-NEXT: entry:
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; CHECK-NEXT: [[XEQY:%.*]] = icmp eq <2 x i64> [[X:%.*]], [[Y:%.*]]
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; CHECK-NEXT: ret <2 x i1> [[XEQY]]
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;
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entry:
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%XeqC = icmp eq <2 x i64> %X, <i64 123, i64 456>
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%YeqC = icmp eq <2 x i64> %Y, <i64 123, i64 456>
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%XeqY = icmp eq <2 x i64> %X, %Y
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%not.YeqC = xor <2 x i1> %YeqC, <i1 true, i1 true>
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%and = select <2 x i1> %not.YeqC, <2 x i1> %XeqY, <2 x i1> <i1 false, i1 false>
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%equal = select <2 x i1> %XeqC, <2 x i1> %YeqC, <2 x i1> %and
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ret <2 x i1> %equal
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}
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define i1 @icmp_equality_test_commute_icmp1(i64 %X, i64 %Y, i64 %Z) {
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; CHECK-LABEL: @icmp_equality_test_commute_icmp1(
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; CHECK-NEXT: entry:
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; CHECK-NEXT: [[XEQY:%.*]] = icmp eq i64 [[Y:%.*]], [[X:%.*]]
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; CHECK-NEXT: ret i1 [[XEQY]]
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;
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entry:
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%XeqZ = icmp eq i64 %Z, %X
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%YeqZ = icmp eq i64 %Z, %Y
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%XeqY = icmp eq i64 %Y, %X
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%not.YeqZ = xor i1 %YeqZ, true
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%and = select i1 %not.YeqZ, i1 %XeqY, i1 false
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%equal = select i1 %XeqZ, i1 %YeqZ, i1 %and
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ret i1 %equal
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}
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define i1 @icmp_equality_test_commute_icmp2(i64 %X, i64 %Y, i64 %Z) {
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; CHECK-LABEL: @icmp_equality_test_commute_icmp2(
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; CHECK-NEXT: [[XEQY:%.*]] = icmp eq i64 [[Y:%.*]], [[X:%.*]]
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; CHECK-NEXT: ret i1 [[XEQY]]
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;
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%XeqZ = icmp eq i64 %Z, %X
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%YeqZ = icmp eq i64 %Y, %Z
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%XeqY = icmp eq i64 %Y, %X
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%not.YeqZ = xor i1 %YeqZ, true
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%and = select i1 %not.YeqZ, i1 %XeqY, i1 false
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%equal = select i1 %XeqZ, i1 %YeqZ, i1 %and
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ret i1 %equal
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}
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define i1 @icmp_equality_test_commute_select1(i64 %X, i64 %Y, i64 %Z) {
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; CHECK-LABEL: @icmp_equality_test_commute_select1(
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; CHECK-NEXT: entry:
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; CHECK-NEXT: [[XEQY:%.*]] = icmp eq i64 [[X:%.*]], [[Y:%.*]]
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; CHECK-NEXT: ret i1 [[XEQY]]
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;
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entry:
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%XeqZ = icmp eq i64 %X, %Z
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%YeqZ = icmp eq i64 %Y, %Z
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%XeqY = icmp eq i64 %X, %Y
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%and = select i1 %YeqZ, i1 false, i1 %XeqY
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%equal = select i1 %XeqZ, i1 %YeqZ, i1 %and
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ret i1 %equal
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}
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define i1 @icmp_equality_test_commute_select2(i64 %X, i64 %Y, i64 %Z) {
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; CHECK-LABEL: @icmp_equality_test_commute_select2(
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; CHECK-NEXT: entry:
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; CHECK-NEXT: [[XEQY:%.*]] = icmp eq i64 [[X:%.*]], [[Y:%.*]]
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; CHECK-NEXT: ret i1 [[XEQY]]
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;
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entry:
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%XeqZ = icmp eq i64 %X, %Z
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%YeqZ = icmp eq i64 %Y, %Z
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%XeqY = icmp eq i64 %X, %Y
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%not.XeqZ = xor i1 %XeqZ, true
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%and = select i1 %YeqZ, i1 false, i1 %XeqY
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%equal = select i1 %not.XeqZ, i1 %and, i1 %YeqZ
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ret i1 %equal
127+
}
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129+
; Negative tests below
130+
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define i1 @icmp_equality_test_wrong_constant(i64 %X, i64 %Y) {
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; CHECK-LABEL: @icmp_equality_test_wrong_constant(
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; CHECK-NEXT: entry:
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; CHECK-NEXT: [[XEQC:%.*]] = icmp eq i64 [[X:%.*]], 0
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; CHECK-NEXT: [[YEQC:%.*]] = icmp eq i64 [[Y:%.*]], 999
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; CHECK-NEXT: [[XEQY:%.*]] = icmp eq i64 [[X]], [[Y]]
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; CHECK-NEXT: [[NOT_YEQC:%.*]] = xor i1 [[YEQC]], true
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; CHECK-NEXT: [[AND:%.*]] = select i1 [[NOT_YEQC]], i1 [[XEQY]], i1 false
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; CHECK-NEXT: [[EQUAL:%.*]] = select i1 [[XEQC]], i1 [[YEQC]], i1 [[AND]]
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; CHECK-NEXT: ret i1 [[EQUAL]]
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;
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entry:
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%XeqC = icmp eq i64 %X, 0
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%YeqC = icmp eq i64 %Y, 999
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%XeqY = icmp eq i64 %X, %Y
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%not.YeqC = xor i1 %YeqC, true
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%and = select i1 %not.YeqC, i1 %XeqY, i1 false
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%equal = select i1 %XeqC, i1 %YeqC, i1 %and
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ret i1 %equal
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}
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define i1 @icmp_equality_test_missing_not(i64 %X, i64 %Y, i64 %Z) {
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; CHECK-LABEL: @icmp_equality_test_missing_not(
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; CHECK-NEXT: [[XEQZ:%.*]] = icmp eq i64 [[X:%.*]], [[Z:%.*]]
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; CHECK-NEXT: [[YEQZ:%.*]] = icmp eq i64 [[Y:%.*]], [[Z]]
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; CHECK-NEXT: [[XEQY:%.*]] = icmp eq i64 [[X]], [[Y]]
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; CHECK-NEXT: [[AND:%.*]] = select i1 [[YEQZ]], i1 [[XEQY]], i1 false
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; CHECK-NEXT: [[EQUAL:%.*]] = select i1 [[XEQZ]], i1 [[YEQZ]], i1 [[AND]]
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; CHECK-NEXT: ret i1 [[EQUAL]]
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;
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%XeqZ = icmp eq i64 %X, %Z
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%YeqZ = icmp eq i64 %Y, %Z
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%XeqY = icmp eq i64 %X, %Y
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%and = select i1 %YeqZ, i1 %XeqY, i1 false
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%equal = select i1 %XeqZ, i1 %YeqZ, i1 %and
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ret i1 %equal
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}
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define i1 @icmp_equality_test_wrong_and(i64 %X, i64 %Y, i64 %Z) {
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; CHECK-LABEL: @icmp_equality_test_wrong_and(
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; CHECK-NEXT: entry:
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; CHECK-NEXT: [[XEQZ:%.*]] = icmp eq i64 [[X:%.*]], [[Z:%.*]]
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; CHECK-NEXT: [[YEQZ:%.*]] = icmp eq i64 [[Y:%.*]], [[Z]]
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; CHECK-NEXT: [[XEQY:%.*]] = icmp eq i64 [[X]], [[Y]]
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; CHECK-NEXT: [[AND:%.*]] = select i1 [[YEQZ]], i1 [[XEQY]], i1 false
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; CHECK-NEXT: [[EQUAL:%.*]] = select i1 [[XEQZ]], i1 [[YEQZ]], i1 [[AND]]
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; CHECK-NEXT: ret i1 [[EQUAL]]
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;
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entry:
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%XeqZ = icmp eq i64 %X, %Z
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%YeqZ = icmp eq i64 %Y, %Z
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%XeqY = icmp eq i64 %X, %Y
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%not.YeqZ = xor i1 %YeqZ, true
184+
%and = select i1 %not.YeqZ, i1 false, i1 %XeqY
185+
%equal = select i1 %XeqZ, i1 %YeqZ, i1 %and
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ret i1 %equal
187+
}
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define i1 @icmp_equality_test_wrong_cmp(i64 %X, i64 %Y, i64 %Z) {
190+
; CHECK-LABEL: @icmp_equality_test_wrong_cmp(
191+
; CHECK-NEXT: entry:
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; CHECK-NEXT: [[XEQZ:%.*]] = icmp eq i64 [[X:%.*]], [[Z:%.*]]
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; CHECK-NEXT: [[YEQZ:%.*]] = icmp eq i64 [[Y:%.*]], [[Z]]
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; CHECK-NEXT: [[XEQY:%.*]] = icmp eq i64 [[X]], 999
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; CHECK-NEXT: [[NOT_YEQZ:%.*]] = xor i1 [[YEQZ]], true
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; CHECK-NEXT: [[AND:%.*]] = select i1 [[NOT_YEQZ]], i1 [[XEQY]], i1 false
197+
; CHECK-NEXT: [[EQUAL:%.*]] = select i1 [[XEQZ]], i1 [[YEQZ]], i1 [[AND]]
198+
; CHECK-NEXT: ret i1 [[EQUAL]]
199+
;
200+
entry:
201+
%XeqZ = icmp eq i64 %X, %Z
202+
%YeqZ = icmp eq i64 %Y, %Z
203+
%XeqY = icmp eq i64 %X, 999
204+
%not.YeqZ = xor i1 %YeqZ, true
205+
%and = select i1 %not.YeqZ, i1 %XeqY, i1 false
206+
%equal = select i1 %XeqZ, i1 %YeqZ, i1 %and
207+
ret i1 %equal
208+
}
209+
210+
define i1 @icmp_equality_test_wrong_equal(i64 %X, i64 %Y, i64 %Z) {
211+
; CHECK-LABEL: @icmp_equality_test_wrong_equal(
212+
; CHECK-NEXT: entry:
213+
; CHECK-NEXT: [[XEQZ:%.*]] = icmp eq i64 [[X:%.*]], [[Z:%.*]]
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; CHECK-NEXT: [[YEQZ:%.*]] = icmp eq i64 [[Y:%.*]], [[Z]]
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; CHECK-NEXT: [[XEQY:%.*]] = icmp eq i64 [[X]], [[Y]]
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; CHECK-NEXT: [[NOT_YEQZ:%.*]] = xor i1 [[YEQZ]], true
217+
; CHECK-NEXT: [[AND:%.*]] = select i1 [[NOT_YEQZ]], i1 [[XEQY]], i1 false
218+
; CHECK-NEXT: [[EQUAL:%.*]] = select i1 [[XEQZ]], i1 [[AND]], i1 [[YEQZ]]
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; CHECK-NEXT: ret i1 [[EQUAL]]
220+
;
221+
entry:
222+
%XeqZ = icmp eq i64 %X, %Z
223+
%YeqZ = icmp eq i64 %Y, %Z
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%XeqY = icmp eq i64 %X, %Y
225+
%not.YeqZ = xor i1 %YeqZ, true
226+
%and = select i1 %not.YeqZ, i1 %XeqY, i1 false
227+
%equal = select i1 %XeqZ, i1 %and, i1 %YeqZ
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ret i1 %equal
229+
}

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