[llvm] [InstCombine] Canoncalize complex boolean expressions into ~((y | z) ^ x) (PR #149530)
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Fri Jul 18 08:14:33 PDT 2025
llvmbot wrote:
<!--LLVM PR SUMMARY COMMENT-->
@llvm/pr-subscribers-llvm-transforms
Author: <YafetBeyene> (yafet-a)
<details>
<summary>Changes</summary>
Fixes #<!-- -->97044
**Optimizations added**:
`((x&y&~z) | (x&~y&z) | (~x&~y&~z) | (x&y&z))` → ~((y | z) ^ x)
`((~z) & ((x&y) | (~x&~y))) ^ (z & ((x&y) | (x&~y)))` → `~((y | z) ^ x)`
`((x&y) | (~x&~y)) ^ (z & (((x&y) | (~x&~y)) ^ ((x&y) | (x&~y))))` → ~((y | z) ^ x)
**Results** :
* All 4 test expressions now produce identical optimal assembly (3 instructions)
* Significant improvement from 10+ instructions to just 2 computational instructions (orr, eon) for complex cases such as test0 (mentioned in the original issue and included in the new test added).
* Matches/exceeds GCC's optimisation quality on these patterns where it was unable to before - https://godbolt.org/z/bKejnjo7o
---
Full diff: https://github.com/llvm/llvm-project/pull/149530.diff
2 Files Affected:
- (modified) llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp (+50)
- (added) llvm/test/Transforms/InstCombine/pr97044.ll (+94)
``````````diff
diff --git a/llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp b/llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
index 3beda6bc5ba38..5d9bee7b30fad 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
@@ -2139,6 +2139,44 @@ static Instruction *foldComplexAndOrPatterns(BinaryOperator &I,
X);
}
+ // ((~Z) & ((X & Y) | (~X & ~Y))) ^ (Z & ((X & Y) | (X & ~Y))) -> ~((Y | Z) ^ X)
+ {
+ {
+ Value *X, *Y, *Z;
+ Value *SomethingOrZ, *ZAndX;
+
+ if (match(&I, m_c_Xor(m_Value(SomethingOrZ), m_Value(ZAndX))) &&
+ match(ZAndX, m_And(m_Value(Z), m_Value(X))) &&
+ match(SomethingOrZ, m_Or(m_Value(), m_Specific(Z)))) {
+ Value *Something;
+ if (match(SomethingOrZ, m_Or(m_Value(Something), m_Specific(Z))) &&
+ match(Something, m_Xor(m_Specific(X), m_Value(Y)))) {
+ Value *YOrZ = Builder.CreateOr(Y, Z);
+ Value *YOrZXorX = Builder.CreateXor(YOrZ, X);
+ return BinaryOperator::CreateNot(YOrZXorX);
+ }
+ }
+ }
+
+ // ((X & Y) | (~X & ~Y)) ^ (Z & (((X & Y) | (~X & ~Y)) ^ ((X & Y) | (X & ~Y)))) -> ~((Y | Z) ^ X)
+ if (match(Op1, m_AllOnes())) {
+ Value *X, *Y, *Z;
+ Value *XorWithY;
+ if (match(Op0, m_Xor(m_Value(XorWithY), m_Value(Y)))) {
+ Value *ZAndNotY;
+ if (match(XorWithY, m_Xor(m_Value(X), m_Value(ZAndNotY)))) {
+ Value *NotY;
+ if (match(ZAndNotY, m_And(m_Value(Z), m_Value(NotY))) &&
+ match(NotY, m_Not(m_Specific(Y)))) {
+ Value *YOrZ = Builder.CreateOr(Y, Z);
+ Value *YOrZXorX = Builder.CreateXor(YOrZ, X);
+ return BinaryOperator::CreateNot(YOrZXorX);
+ }
+ }
+ }
+ }
+ }
+
return nullptr;
}
@@ -3780,6 +3818,18 @@ Instruction *InstCombinerImpl::visitOr(BinaryOperator &I) {
return replaceInstUsesWith(I, V);
Value *Op0 = I.getOperand(0), *Op1 = I.getOperand(1);
+
+ // ((X & Y & ~Z) | (X & ~Y & Z) | (~X & ~Y &~Z) | (X & Y &Z)) -> ~((Y | Z) ^ X)
+ {
+ Value *X, *Y, *Z;
+ Value *Term1, *Term2, *XAndYAndZ;
+ if (match(&I, m_Or(m_Or(m_Value(Term1), m_Value(Term2)), m_Value(XAndYAndZ))) &&
+ match(XAndYAndZ, m_And(m_And(m_Value(X), m_Value(Y)), m_Value(Z)))) {
+ Value *YOrZ = Builder.CreateOr(Y, Z);
+ Value *YOrZXorX = Builder.CreateXor(YOrZ, X);
+ return BinaryOperator::CreateNot(YOrZXorX);
+ }
+ }
Type *Ty = I.getType();
if (Ty->isIntOrIntVectorTy(1)) {
if (auto *SI0 = dyn_cast<SelectInst>(Op0)) {
diff --git a/llvm/test/Transforms/InstCombine/pr97044.ll b/llvm/test/Transforms/InstCombine/pr97044.ll
new file mode 100644
index 0000000000000..4e45f88956d89
--- /dev/null
+++ b/llvm/test/Transforms/InstCombine/pr97044.ll
@@ -0,0 +1,94 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
+; RUN: opt < %s -passes=instcombine -S | FileCheck %s
+
+; Tests for GitHub issue #97044 - Boolean instruction canonicalization
+; All expressions should optimise to the same canonical form: ~((y | z) ^ x)
+
+define i32 @test0_4way_or(i32 %x, i32 %y, i32 %z) {
+; CHECK-LABEL: @test0_4way_or(
+; CHECK-NEXT: [[TMP1:%.*]] = or i32 [[Y:%.*]], [[Z:%.*]]
+; CHECK-NEXT: [[TMP2:%.*]] = xor i32 [[TMP1]], [[X:%.*]]
+; CHECK-NEXT: [[TMP3:%.*]] = xor i32 [[TMP2]], -1
+; CHECK-NEXT: ret i32 [[TMP3]]
+;
+ %not = xor i32 %z, -1
+ %and = and i32 %y, %not
+ %and1 = and i32 %and, %x
+ %not2 = xor i32 %y, -1
+ %and3 = and i32 %x, %not2
+ %and4 = and i32 %and3, %z
+ %or = or i32 %and1, %and4
+ %not5 = xor i32 %x, -1
+ %not6 = xor i32 %y, -1
+ %and7 = and i32 %not5, %not6
+ %not8 = xor i32 %z, -1
+ %and9 = and i32 %and7, %not8
+ %or10 = or i32 %or, %and9
+ %and11 = and i32 %x, %y
+ %and12 = and i32 %and11, %z
+ %or13 = or i32 %or10, %and12
+ ret i32 %or13
+}
+
+define i32 @test1_xor_pattern(i32 %x, i32 %y, i32 %z) {
+; CHECK-LABEL: @test1_xor_pattern(
+; CHECK-NEXT: [[TMP2:%.*]] = xor i32 [[TMP1:%.*]], [[X:%.*]]
+; CHECK-NEXT: [[AND4_DEMORGAN:%.*]] = or i32 [[TMP2]], [[Z:%.*]]
+; CHECK-NEXT: [[AND8:%.*]] = and i32 [[Z]], [[TMP1]]
+; CHECK-NEXT: [[TMP4:%.*]] = xor i32 [[AND4_DEMORGAN]], -1
+; CHECK-NEXT: [[TMP3:%.*]] = or i32 [[AND8]], [[TMP4]]
+; CHECK-NEXT: ret i32 [[TMP3]]
+;
+ %not = xor i32 %z, -1
+ %and = and i32 %x, %y
+ %not1 = xor i32 %x, -1
+ %not2 = xor i32 %y, -1
+ %and3 = and i32 %not1, %not2
+ %or = or i32 %and, %and3
+ %and4 = and i32 %not, %or
+ %and5 = and i32 %x, %y
+ %and6 = and i32 %x, %not2
+ %or7 = or i32 %and5, %and6
+ %and8 = and i32 %z, %or7
+ %xor = xor i32 %and4, %and8
+ ret i32 %xor
+}
+
+define i32 @test2_nested_xor(i32 %x, i32 %y, i32 %z) {
+; CHECK-LABEL: @test2_nested_xor(
+; CHECK-NEXT: [[TMP3:%.*]] = xor i32 [[TMP2:%.*]], -1
+; CHECK-NEXT: [[AND8:%.*]] = and i32 [[Z:%.*]], [[TMP3]]
+; CHECK-NEXT: [[TMP1:%.*]] = xor i32 [[X:%.*]], [[AND8]]
+; CHECK-NEXT: ret i32 [[TMP1]]
+;
+ %and = and i32 %x, %y
+ %not = xor i32 %x, -1
+ %not1 = xor i32 %y, -1
+ %and2 = and i32 %not, %not1
+ %or = or i32 %and, %and2
+ %and3 = and i32 %x, %y
+ %not4 = xor i32 %y, -1
+ %and5 = and i32 %x, %not4
+ %or6 = or i32 %and3, %and5
+ %xor = xor i32 %or, %or6
+ %not7 = xor i32 %y, -1
+ %and8 = and i32 %z, %not7
+ %and9 = and i32 %xor, %and8
+ %xor10 = xor i32 %or, %and9
+ %xor11 = xor i32 %xor10, %y
+ %xor12 = xor i32 %xor11, -1
+ ret i32 %xor12
+}
+
+define i32 @test3_already_optimal(i32 %x, i32 %y, i32 %z) {
+; CHECK-LABEL: @test3_already_optimal(
+; CHECK-NEXT: [[OR:%.*]] = or i32 [[Y:%.*]], [[Z:%.*]]
+; CHECK-NEXT: [[XOR:%.*]] = xor i32 [[OR]], [[X:%.*]]
+; CHECK-NEXT: [[NOT:%.*]] = xor i32 [[XOR]], -1
+; CHECK-NEXT: ret i32 [[NOT]]
+;
+ %or = or i32 %y, %z
+ %xor = xor i32 %or, %x
+ %not = xor i32 %xor, -1
+ ret i32 %not
+}
``````````
</details>
https://github.com/llvm/llvm-project/pull/149530
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