[llvm] [InstCombine] Fold `icmp eq/ne (X *nw Z), (Y *nw Z) -> icmp eq/ne Z, 0` when `X != Y` (PR #110413)

[via llvm-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-llvm-transforms

Author: Yingwei Zheng (dtcxzyw)

<details>
<summary>Changes</summary>

Alive2: https://alive2.llvm.org/ce/z/9oDP6K
I found this pattern in https://github.com/casadi/casadi/blob/04e75858d7e626dda62d83b862fc89fc26f52745/casadi/core/repmat.cpp#L70-L78.


---
Full diff: https://github.com/llvm/llvm-project/pull/110413.diff


2 Files Affected:

- (modified) llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp (+5) 
- (modified) llvm/test/Transforms/InstCombine/icmp-mul.ll (+107) 


``````````diff
diff --git a/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp b/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
index b1215bb4d83b0f..e3f4925024e65c 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
@@ -5282,6 +5282,11 @@ Instruction *InstCombinerImpl::foldICmpBinOp(ICmpInst &I,
           match(Op1, m_c_Mul(m_Specific(Z), m_Value(Y)))))) {
       bool NonZero;
       if (ICmpInst::isEquality(Pred)) {
+        // If X != Y, fold (X *nw Z) eq/ne (Y *nw Z) -> Z eq/ne 0
+        if (((Op0HasNSW && Op1HasNSW) || (Op0HasNUW && Op1HasNUW)) &&
+            isKnownNonEqual(X, Y, DL, &AC, &I, &DT))
+          return new ICmpInst(Pred, Z, Constant::getNullValue(Z->getType()));
+
         KnownBits ZKnown = computeKnownBits(Z, 0, &I);
         // if Z % 2 != 0
         //    X * Z eq/ne Y * Z -> X eq/ne Y
diff --git a/llvm/test/Transforms/InstCombine/icmp-mul.ll b/llvm/test/Transforms/InstCombine/icmp-mul.ll
index 3ba21abb069ba7..7ce43908c62cd0 100644
--- a/llvm/test/Transforms/InstCombine/icmp-mul.ll
+++ b/llvm/test/Transforms/InstCombine/icmp-mul.ll
@@ -1223,3 +1223,110 @@ define <2 x i1> @mul_mixed_nsw_nuw_xy_z_setnonzero_vec_ule(<2 x i8> %x, <2 x i8>
   %cmp = icmp ule <2 x i8> %muly, %mulx
   ret <2 x i1> %cmp
 }
+
+define i1 @icmp_eq_mul_nsw_nonequal(i8 %a, i8 %c) {
+; CHECK-LABEL: @icmp_eq_mul_nsw_nonequal(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    [[CMP:%.*]] = icmp eq i8 [[C:%.*]], 0
+; CHECK-NEXT:    ret i1 [[CMP]]
+;
+entry:
+  %b = add i8 %a, 1
+  %mul1 = mul nsw i8 %a, %c
+  %mul2 = mul nsw i8 %b, %c
+  %cmp = icmp eq i8 %mul1, %mul2
+  ret i1 %cmp
+}
+
+define i1 @icmp_eq_mul_nuw_nonequal(i8 %a, i8 %c) {
+; CHECK-LABEL: @icmp_eq_mul_nuw_nonequal(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    [[CMP:%.*]] = icmp eq i8 [[C:%.*]], 0
+; CHECK-NEXT:    ret i1 [[CMP]]
+;
+entry:
+  %b = add i8 %a, 1
+  %mul1 = mul nuw i8 %a, %c
+  %mul2 = mul nuw i8 %b, %c
+  %cmp = icmp eq i8 %mul1, %mul2
+  ret i1 %cmp
+}
+
+define i1 @icmp_eq_mul_nsw_nonequal_commuted(i8 %a, i8 %c) {
+; CHECK-LABEL: @icmp_eq_mul_nsw_nonequal_commuted(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    [[CMP:%.*]] = icmp eq i8 [[C:%.*]], 0
+; CHECK-NEXT:    ret i1 [[CMP]]
+;
+entry:
+  %b = add i8 %a, 1
+  %mul1 = mul nsw i8 %a, %c
+  %mul2 = mul nsw i8 %c, %b
+  %cmp = icmp eq i8 %mul1, %mul2
+  ret i1 %cmp
+}
+
+define i1 @icmp_ne_mul_nsw_nonequal(i8 %a, i8 %c) {
+; CHECK-LABEL: @icmp_ne_mul_nsw_nonequal(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    [[CMP:%.*]] = icmp ne i8 [[C:%.*]], 0
+; CHECK-NEXT:    ret i1 [[CMP]]
+;
+entry:
+  %b = add i8 %a, 1
+  %mul1 = mul nsw i8 %a, %c
+  %mul2 = mul nsw i8 %b, %c
+  %cmp = icmp ne i8 %mul1, %mul2
+  ret i1 %cmp
+}
+
+; Negative tests
+
+define i1 @icmp_eq_mul_nsw_mayequal(i8 %a, i8 %b, i8 %c) {
+; CHECK-LABEL: @icmp_eq_mul_nsw_mayequal(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    [[MUL1:%.*]] = mul nsw i8 [[A:%.*]], [[C:%.*]]
+; CHECK-NEXT:    [[MUL2:%.*]] = mul nsw i8 [[B:%.*]], [[C]]
+; CHECK-NEXT:    [[CMP:%.*]] = icmp eq i8 [[MUL1]], [[MUL2]]
+; CHECK-NEXT:    ret i1 [[CMP]]
+;
+entry:
+  %mul1 = mul nsw i8 %a, %c
+  %mul2 = mul nsw i8 %b, %c
+  %cmp = icmp eq i8 %mul1, %mul2
+  ret i1 %cmp
+}
+
+define i1 @icmp_eq_mul_nsw_nuw_nonequal(i8 %a, i8 %c) {
+; CHECK-LABEL: @icmp_eq_mul_nsw_nuw_nonequal(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    [[B:%.*]] = add i8 [[A:%.*]], 1
+; CHECK-NEXT:    [[MUL1:%.*]] = mul nsw i8 [[A]], [[C:%.*]]
+; CHECK-NEXT:    [[MUL2:%.*]] = mul nuw i8 [[B]], [[C]]
+; CHECK-NEXT:    [[CMP:%.*]] = icmp eq i8 [[MUL1]], [[MUL2]]
+; CHECK-NEXT:    ret i1 [[CMP]]
+;
+entry:
+  %b = add i8 %a, 1
+  %mul1 = mul nsw i8 %a, %c
+  %mul2 = mul nuw i8 %b, %c
+  %cmp = icmp eq i8 %mul1, %mul2
+  ret i1 %cmp
+}
+
+define i1 @icmp_ult_mul_nsw_nonequal(i8 %a, i8 %c) {
+; CHECK-LABEL: @icmp_ult_mul_nsw_nonequal(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    [[B:%.*]] = add i8 [[A:%.*]], 1
+; CHECK-NEXT:    [[MUL1:%.*]] = mul nsw i8 [[A]], [[C:%.*]]
+; CHECK-NEXT:    [[MUL2:%.*]] = mul nsw i8 [[B]], [[C]]
+; CHECK-NEXT:    [[CMP:%.*]] = icmp ult i8 [[MUL1]], [[MUL2]]
+; CHECK-NEXT:    ret i1 [[CMP]]
+;
+entry:
+  %b = add i8 %a, 1
+  %mul1 = mul nsw i8 %a, %c
+  %mul2 = mul nsw i8 %b, %c
+  %cmp = icmp ult i8 %mul1, %mul2
+  ret i1 %cmp
+}

``````````

</details>


https://github.com/llvm/llvm-project/pull/110413