[llvm] [InstCombine] Handle trunc i1 pattern in eq-of-parts fold (PR #112704)

[via llvm-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-llvm-transforms

Author: Nikita Popov (nikic)

<details>
<summary>Changes</summary>

Equality/inequality of the low bit can be represented by `(trunc (xor x, y) to i1)`, possibly with an extra not. We have to handle this in the eq-of-parts fold now that we no longer canonicalize this to a masked icmp.

Proofs: https://alive2.llvm.org/ce/z/qidkzq

Fixes https://github.com/llvm/llvm-project/issues/110919.

---
Full diff: https://github.com/llvm/llvm-project/pull/112704.diff


3 Files Affected:

- (modified) llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp (+17-6) 
- (modified) llvm/lib/Transforms/InstCombine/InstCombineInternal.h (+1-1) 
- (modified) llvm/test/Transforms/InstCombine/eq-of-parts.ll (+2-9) 


``````````diff
diff --git a/llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp b/llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
index 8112255a0b6c45..629ac859c06e35 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
@@ -1185,14 +1185,25 @@ static Value *extractIntPart(const IntPart &P, IRBuilderBase &Builder) {
 /// (icmp eq X0, Y0) & (icmp eq X1, Y1) -> icmp eq X01, Y01
 /// (icmp ne X0, Y0) | (icmp ne X1, Y1) -> icmp ne X01, Y01
 /// where X0, X1 and Y0, Y1 are adjacent parts extracted from an integer.
-Value *InstCombinerImpl::foldEqOfParts(ICmpInst *Cmp0, ICmpInst *Cmp1,
-                                       bool IsAnd) {
+Value *InstCombinerImpl::foldEqOfParts(Value *Cmp0, Value *Cmp1, bool IsAnd) {
   if (!Cmp0->hasOneUse() || !Cmp1->hasOneUse())
     return nullptr;
 
   CmpInst::Predicate Pred = IsAnd ? CmpInst::ICMP_EQ : CmpInst::ICMP_NE;
-  auto GetMatchPart = [&](ICmpInst *Cmp,
+  auto GetMatchPart = [&](Value *CmpV,
                           unsigned OpNo) -> std::optional<IntPart> {
+    Value *X, *Y;
+    // icmp ne (and x, 1), (and y, 1) <=> trunc (xor x, y) to i1
+    // icmp eq (and x, 1), (and y, 1) <=> not (trunc (xor x, y) to i1)
+    if (Pred == CmpInst::ICMP_NE
+            ? match(CmpV, m_Trunc(m_Xor(m_Value(X), m_Value(Y))))
+            : match(CmpV, m_Not(m_Trunc(m_Xor(m_Value(X), m_Value(Y))))))
+      return {{OpNo == 0 ? X : Y, 0, 1}};
+
+    auto *Cmp = dyn_cast<ICmpInst>(CmpV);
+    if (!Cmp)
+      return std::nullopt;
+
     if (Pred == Cmp->getPredicate())
       return matchIntPart(Cmp->getOperand(OpNo));
 
@@ -3413,9 +3424,6 @@ Value *InstCombinerImpl::foldAndOrOfICmps(ICmpInst *LHS, ICmpInst *RHS,
       return X;
   }
 
-  if (Value *X = foldEqOfParts(LHS, RHS, IsAnd))
-    return X;
-
   // (icmp ne A, 0) | (icmp ne B, 0) --> (icmp ne (A|B), 0)
   // (icmp eq A, 0) & (icmp eq B, 0) --> (icmp eq (A|B), 0)
   // TODO: Remove this and below when foldLogOpOfMaskedICmps can handle undefs.
@@ -3538,6 +3546,9 @@ Value *InstCombinerImpl::foldBooleanAndOr(Value *LHS, Value *RHS,
       if (Value *Res = foldLogicOfFCmps(LHSCmp, RHSCmp, IsAnd, IsLogical))
         return Res;
 
+  if (Value *Res = foldEqOfParts(LHS, RHS, IsAnd))
+    return Res;
+
   return nullptr;
 }
 
diff --git a/llvm/lib/Transforms/InstCombine/InstCombineInternal.h b/llvm/lib/Transforms/InstCombine/InstCombineInternal.h
index 7a060cdab2d37d..6c38725939f2a6 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineInternal.h
+++ b/llvm/lib/Transforms/InstCombine/InstCombineInternal.h
@@ -411,7 +411,7 @@ class LLVM_LIBRARY_VISIBILITY InstCombinerImpl final
                           bool IsAnd, bool IsLogical = false);
   Value *foldXorOfICmps(ICmpInst *LHS, ICmpInst *RHS, BinaryOperator &Xor);
 
-  Value *foldEqOfParts(ICmpInst *Cmp0, ICmpInst *Cmp1, bool IsAnd);
+  Value *foldEqOfParts(Value *Cmp0, Value *Cmp1, bool IsAnd);
 
   Value *foldAndOrOfICmpsUsingRanges(ICmpInst *ICmp1, ICmpInst *ICmp2,
                                      bool IsAnd);
diff --git a/llvm/test/Transforms/InstCombine/eq-of-parts.ll b/llvm/test/Transforms/InstCombine/eq-of-parts.ll
index afe5d6af1fcd49..5bcfef812c6bb6 100644
--- a/llvm/test/Transforms/InstCombine/eq-of-parts.ll
+++ b/llvm/test/Transforms/InstCombine/eq-of-parts.ll
@@ -1441,11 +1441,7 @@ define i1 @ne_optimized_highbits_cmp_todo_overlapping(i32 %x, i32 %y) {
 
 define i1 @and_trunc_i1(i8 %a1, i8 %a2) {
 ; CHECK-LABEL: @and_trunc_i1(
-; CHECK-NEXT:    [[XOR:%.*]] = xor i8 [[A1:%.*]], [[A2:%.*]]
-; CHECK-NEXT:    [[CMP:%.*]] = icmp ult i8 [[XOR]], 2
-; CHECK-NEXT:    [[LOBIT:%.*]] = trunc i8 [[XOR]] to i1
-; CHECK-NEXT:    [[LOBIT_INV:%.*]] = xor i1 [[LOBIT]], true
-; CHECK-NEXT:    [[AND:%.*]] = and i1 [[CMP]], [[LOBIT_INV]]
+; CHECK-NEXT:    [[AND:%.*]] = icmp eq i8 [[A1:%.*]], [[A2:%.*]]
 ; CHECK-NEXT:    ret i1 [[AND]]
 ;
   %xor = xor i8 %a1, %a2
@@ -1494,10 +1490,7 @@ define i1 @and_trunc_i1_wrong_operands(i8 %a1, i8 %a2, i8 %a3) {
 
 define i1 @or_trunc_i1(i64 %a1, i64 %a2) {
 ; CHECK-LABEL: @or_trunc_i1(
-; CHECK-NEXT:    [[XOR:%.*]] = xor i64 [[A2:%.*]], [[A1:%.*]]
-; CHECK-NEXT:    [[CMP:%.*]] = icmp ugt i64 [[XOR]], 1
-; CHECK-NEXT:    [[TRUNC:%.*]] = trunc i64 [[XOR]] to i1
-; CHECK-NEXT:    [[OR:%.*]] = or i1 [[CMP]], [[TRUNC]]
+; CHECK-NEXT:    [[OR:%.*]] = icmp ne i64 [[A2:%.*]], [[A1:%.*]]
 ; CHECK-NEXT:    ret i1 [[OR]]
 ;
   %xor = xor i64 %a2, %a1

``````````

</details>


https://github.com/llvm/llvm-project/pull/112704