[llvm] [InstCombine] Fold `(icmp eq/ne (add nuw x, y), 0)` -> `(icmp eq/ne (or x, y), 0)` (PR #88088)

[via llvm-commits]

https://github.com/goldsteinn updated https://github.com/llvm/llvm-project/pull/88088

>From 98bfa63a658ce09fb37625a6c92bf0de0338f91b Mon Sep 17 00:00:00 2001
From: Noah Goldstein <goldstein.w.n at gmail.com>
Date: Sun, 7 Apr 2024 14:40:21 -0500
Subject: [PATCH 1/2] [InstCombine] Add tests for folding `(icmp eq/ne (add nuw
 x, y), 0)`; NFC

---
 llvm/test/Transforms/InstCombine/icmp-add.ll | 24 ++++++++++++++++++++
 1 file changed, 24 insertions(+)

diff --git a/llvm/test/Transforms/InstCombine/icmp-add.ll b/llvm/test/Transforms/InstCombine/icmp-add.ll
index b99ed20d7d431c..6f990890dbb2cf 100644
--- a/llvm/test/Transforms/InstCombine/icmp-add.ll
+++ b/llvm/test/Transforms/InstCombine/icmp-add.ll
@@ -3003,4 +3003,28 @@ define i1 @icmp_dec_notnonzero(i8 %x) {
   ret i1 %c
 }
 
+define i1 @icmp_addnuw_nonzero(i8 %x, i8 %y) {
+; CHECK-LABEL: @icmp_addnuw_nonzero(
+; CHECK-NEXT:    [[I:%.*]] = sub i8 0, [[Y:%.*]]
+; CHECK-NEXT:    [[C:%.*]] = icmp eq i8 [[I]], [[X:%.*]]
+; CHECK-NEXT:    ret i1 [[C]]
+;
+  %i = add nuw i8 %x, %y
+  %c = icmp eq i8 %i, 0
+  ret i1 %c
+}
+
+define i1 @icmp_addnuw_nonzero_fail_multiuse(i32 %x, i32 %y) {
+; CHECK-LABEL: @icmp_addnuw_nonzero_fail_multiuse(
+; CHECK-NEXT:    [[I:%.*]] = add nuw i32 [[X:%.*]], [[Y:%.*]]
+; CHECK-NEXT:    [[C:%.*]] = icmp eq i32 [[I]], 0
+; CHECK-NEXT:    call void @use(i32 [[I]])
+; CHECK-NEXT:    ret i1 [[C]]
+;
+  %i = add nuw i32 %x, %y
+  %c = icmp eq i32 %i, 0
+  call void @use(i32 %i)
+  ret i1 %c
+}
+
 declare void @llvm.assume(i1)

>From 08ea7f35cf9602e9e0de91e31e989e7a46dfb9fb Mon Sep 17 00:00:00 2001
From: Noah Goldstein <goldstein.w.n at gmail.com>
Date: Sun, 7 Apr 2024 14:38:03 -0500
Subject: [PATCH 2/2] [InstCombine] Fold `(icmp eq/ne (add nuw x, y), 0)` ->
 `(icmp eq/ne (or x, y), 0)`

`(icmp eq/ne (or x, y), 0)` is probably easier to analyze than `(icmp
eq/ne x, -y)`

Proof: https://alive2.llvm.org/ce/z/2-VTb6
---
 .../InstCombine/InstCombineCompares.cpp          |  5 +++++
 llvm/test/Transforms/InstCombine/icmp-add.ll     | 16 ++++++----------
 2 files changed, 11 insertions(+), 10 deletions(-)

diff --git a/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp b/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
index db302d7e526844..53aa84d53f3085 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
@@ -3453,6 +3453,11 @@ Instruction *InstCombinerImpl::foldICmpBinOpEqualityWithConstant(
       if (Value *NegVal = dyn_castNegVal(BOp0))
         return new ICmpInst(Pred, NegVal, BOp1);
       if (BO->hasOneUse()) {
+        // (add nuw A, B) != 0 -> (or A, B) != 0
+        if (match(BO, m_NUWAdd(m_Value(), m_Value()))) {
+          Value *Or = Builder.CreateOr(BOp0, BOp1);
+          return new ICmpInst(Pred, Or, Constant::getNullValue(BO->getType()));
+        }
         Value *Neg = Builder.CreateNeg(BOp1);
         Neg->takeName(BO);
         return new ICmpInst(Pred, BOp0, Neg);
diff --git a/llvm/test/Transforms/InstCombine/icmp-add.ll b/llvm/test/Transforms/InstCombine/icmp-add.ll
index 6f990890dbb2cf..6b4e5a5372c523 100644
--- a/llvm/test/Transforms/InstCombine/icmp-add.ll
+++ b/llvm/test/Transforms/InstCombine/icmp-add.ll
@@ -9,10 +9,8 @@ declare void @use(i32)
 define i1 @cvt_icmp_0_zext_plus_zext_eq_i16(i16 %arg, i16 %arg1) {
 ; CHECK-LABEL: @cvt_icmp_0_zext_plus_zext_eq_i16(
 ; CHECK-NEXT:  bb:
-; CHECK-NEXT:    [[I:%.*]] = zext i16 [[ARG:%.*]] to i32
-; CHECK-NEXT:    [[I2:%.*]] = zext i16 [[ARG1:%.*]] to i32
-; CHECK-NEXT:    [[I3:%.*]] = sub nsw i32 0, [[I]]
-; CHECK-NEXT:    [[I4:%.*]] = icmp eq i32 [[I2]], [[I3]]
+; CHECK-NEXT:    [[TMP0:%.*]] = or i16 [[ARG1:%.*]], [[ARG:%.*]]
+; CHECK-NEXT:    [[I4:%.*]] = icmp eq i16 [[TMP0]], 0
 ; CHECK-NEXT:    ret i1 [[I4]]
 ;
 bb:
@@ -27,10 +25,8 @@ bb:
 define i1 @cvt_icmp_0_zext_plus_zext_eq_i8(i8 %arg, i8 %arg1) {
 ; CHECK-LABEL: @cvt_icmp_0_zext_plus_zext_eq_i8(
 ; CHECK-NEXT:  bb:
-; CHECK-NEXT:    [[I:%.*]] = zext i8 [[ARG:%.*]] to i32
-; CHECK-NEXT:    [[I2:%.*]] = zext i8 [[ARG1:%.*]] to i32
-; CHECK-NEXT:    [[I3:%.*]] = sub nsw i32 0, [[I]]
-; CHECK-NEXT:    [[I4:%.*]] = icmp eq i32 [[I2]], [[I3]]
+; CHECK-NEXT:    [[TMP0:%.*]] = or i8 [[ARG1:%.*]], [[ARG:%.*]]
+; CHECK-NEXT:    [[I4:%.*]] = icmp eq i8 [[TMP0]], 0
 ; CHECK-NEXT:    ret i1 [[I4]]
 ;
 bb:
@@ -3005,8 +3001,8 @@ define i1 @icmp_dec_notnonzero(i8 %x) {
 
 define i1 @icmp_addnuw_nonzero(i8 %x, i8 %y) {
 ; CHECK-LABEL: @icmp_addnuw_nonzero(
-; CHECK-NEXT:    [[I:%.*]] = sub i8 0, [[Y:%.*]]
-; CHECK-NEXT:    [[C:%.*]] = icmp eq i8 [[I]], [[X:%.*]]
+; CHECK-NEXT:    [[TMP1:%.*]] = or i8 [[X:%.*]], [[Y:%.*]]
+; CHECK-NEXT:    [[C:%.*]] = icmp eq i8 [[TMP1]], 0
 ; CHECK-NEXT:    ret i1 [[C]]
 ;
   %i = add nuw i8 %x, %y