[llvm] (InstCombine) Fold (x | y) > x + y -> x > x + y (PR #164325)

[via llvm-commits]

https://github.com/AZero13 created https://github.com/llvm/llvm-project/pull/164325

Alive2: https://alive2.llvm.org/ce/z/oAoh6c

>From 684ab516eadfe9d4a3f2375272e3aedb71110ded Mon Sep 17 00:00:00 2001
From: AZero13 <gfunni234 at gmail.com>
Date: Mon, 20 Oct 2025 16:07:34 -0400
Subject: [PATCH 1/2] Pre-commit test (NFC)

---
 llvm/test/Transforms/InstCombine/icmp.ll | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)

diff --git a/llvm/test/Transforms/InstCombine/icmp.ll b/llvm/test/Transforms/InstCombine/icmp.ll
index 696208b903798..73ee48d2ce44e 100644
--- a/llvm/test/Transforms/InstCombine/icmp.ll
+++ b/llvm/test/Transforms/InstCombine/icmp.ll
@@ -6240,3 +6240,19 @@ entry:
   %cmp = icmp ult i8 %p0, %p1
   ret i1 %cmp
 }
+
+; Transform (x | y) > x + y into x > x + y
+; This is valid because (x | y) >= x always, so (x | y) > x + y is equivalent to x > x + y
+define i1 @uaddo_or(i32 %x, i32 %y) {
+; CHECK-LABEL: define i1 @uaddo_or(
+; CHECK-SAME: i32 [[X:%.*]], i32 [[Y:%.*]]) {
+; CHECK-NEXT:    [[OR:%.*]] = or i32 [[Y]], [[X]]
+; CHECK-NEXT:    [[ADD:%.*]] = add i32 [[Y]], [[X]]
+; CHECK-NEXT:    [[CMP:%.*]] = icmp ugt i32 [[OR]], [[ADD]]
+; CHECK-NEXT:    ret i1 [[CMP]]
+;
+  %or = or i32 %y, %x
+  %add = add i32 %y, %x
+  %cmp = icmp ugt i32 %or, %add
+  ret i1 %cmp
+}

>From 5275ee3e340fa8d1ee1a2364e76ae6bd4eaaa820 Mon Sep 17 00:00:00 2001
From: AZero13 <gfunni234 at gmail.com>
Date: Mon, 20 Oct 2025 16:21:10 -0400
Subject: [PATCH 2/2] Fold (x | y) > x + y -> x > x + y

Alive2: https://alive2.llvm.org/ce/z/oAoh6c
---
 .../InstCombine/InstCombineCompares.cpp       | 20 +++++++++++++++++++
 llvm/test/Transforms/InstCombine/icmp.ll      | 19 +++++++++++++++---
 2 files changed, 36 insertions(+), 3 deletions(-)

diff --git a/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp b/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
index fba1ccf2c8c9b..212a47af2cd20 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
@@ -7855,6 +7855,26 @@ Instruction *InstCombinerImpl::visitICmpInst(ICmpInst &I) {
       }
     }
 
+    // Transform (x | y) > x + y into x > x + y
+    Value *OrLHS, *OrRHS, *AddLHS, *AddRHS;
+    if (match(Op0, m_Or(m_Value(OrLHS), m_Value(OrRHS))) &&
+        match(Op1, m_Add(m_Value(AddLHS), m_Value(AddRHS))) &&
+        ((OrLHS == AddLHS && OrRHS == AddRHS) ||
+         (OrLHS == AddRHS && OrRHS == AddLHS))) {
+      // Replace (x | y) with x in the comparison
+      replaceOperand(I, 0, AddLHS);
+      return &I;
+    }
+
+    if (match(Op0, m_Add(m_Value(AddLHS), m_Value(AddRHS))) &&
+        match(Op1, m_Or(m_Value(OrLHS), m_Value(OrRHS))) &&
+        ((AddLHS == OrLHS && AddRHS == OrRHS) ||
+         (AddLHS == OrRHS && AddRHS == OrLHS))) {
+      // Replace (x | y) with x in the comparison
+      replaceOperand(I, 1, AddLHS);
+      return &I;
+    }
+
     Instruction *AddI = nullptr;
     if (match(&I, m_UAddWithOverflow(m_Value(X), m_Value(Y),
                                      m_Instruction(AddI))) &&
diff --git a/llvm/test/Transforms/InstCombine/icmp.ll b/llvm/test/Transforms/InstCombine/icmp.ll
index 73ee48d2ce44e..721c89fac1e44 100644
--- a/llvm/test/Transforms/InstCombine/icmp.ll
+++ b/llvm/test/Transforms/InstCombine/icmp.ll
@@ -6246,9 +6246,8 @@ entry:
 define i1 @uaddo_or(i32 %x, i32 %y) {
 ; CHECK-LABEL: define i1 @uaddo_or(
 ; CHECK-SAME: i32 [[X:%.*]], i32 [[Y:%.*]]) {
-; CHECK-NEXT:    [[OR:%.*]] = or i32 [[Y]], [[X]]
-; CHECK-NEXT:    [[ADD:%.*]] = add i32 [[Y]], [[X]]
-; CHECK-NEXT:    [[CMP:%.*]] = icmp ugt i32 [[OR]], [[ADD]]
+; CHECK-NEXT:    [[TMP1:%.*]] = xor i32 [[Y]], -1
+; CHECK-NEXT:    [[CMP:%.*]] = icmp ugt i32 [[X]], [[TMP1]]
 ; CHECK-NEXT:    ret i1 [[CMP]]
 ;
   %or = or i32 %y, %x
@@ -6256,3 +6255,17 @@ define i1 @uaddo_or(i32 %x, i32 %y) {
   %cmp = icmp ugt i32 %or, %add
   ret i1 %cmp
 }
+
+; Transform x + y < (x | y) into x + y < x (equivalent to x > x + y)
+define i1 @uaddo_or_reverse(i32 %x, i32 %y) {
+; CHECK-LABEL: define i1 @uaddo_or_reverse(
+; CHECK-SAME: i32 [[X:%.*]], i32 [[Y:%.*]]) {
+; CHECK-NEXT:    [[TMP1:%.*]] = xor i32 [[Y]], -1
+; CHECK-NEXT:    [[CMP:%.*]] = icmp ugt i32 [[X]], [[TMP1]]
+; CHECK-NEXT:    ret i1 [[CMP]]
+;
+  %add = add i32 %y, %x
+  %or = or i32 %y, %x
+  %cmp = icmp ult i32 %add, %or
+  ret i1 %cmp
+}