From e2ee2e413268c6acfe0c9521dce815d17c4b7829 Mon Sep 17 00:00:00 2001
From: Andreas Jonson <andjo403@hotmail.com>
Date: Thu, 6 Nov 2025 18:34:37 +0100
Subject: [PATCH] [InstCombine] Fold operation into select, when one operand is
 zext of select's condition

eg fold binop(select cond, C1, C2, zext(cond)) to
select cond, C11, C22
---
 .../InstCombine/InstructionCombining.cpp      |  3 ++
 .../Transforms/InstCombine/binop-select.ll    | 29 ++++---------------
 2 files changed, 9 insertions(+), 23 deletions(-)

diff --git a/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp b/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
index b158e0f626850..27ec6c6cb78a3 100644
--- a/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
@@ -1758,6 +1758,9 @@ static Value *simplifyOperationIntoSelectOperand(Instruction &I, SelectInst *SI,
                                     m_Specific(Op), m_Value(V))) &&
                isGuaranteedNotToBeUndefOrPoison(V)) {
       // Pass
+    } else if (match(Op, m_ZExt(m_Specific(SI->getCondition())))) {
+      V = IsTrueArm ? ConstantInt::get(Op->getType(), 1)
+                    : ConstantInt::getNullValue(Op->getType());
     } else {
       V = Op;
     }
diff --git a/llvm/test/Transforms/InstCombine/binop-select.ll b/llvm/test/Transforms/InstCombine/binop-select.ll
index fe1ec9014f188..9e336ad104599 100644
--- a/llvm/test/Transforms/InstCombine/binop-select.ll
+++ b/llvm/test/Transforms/InstCombine/binop-select.ll
@@ -406,10 +406,7 @@ define i32 @ashr_sel_op1_use(i1 %b) {
 
 define i8 @commonArgWithOr0(i1 %arg0) {
 ; CHECK-LABEL: @commonArgWithOr0(
-; CHECK-NEXT:    [[V0:%.*]] = zext i1 [[ARG0:%.*]] to i8
-; CHECK-NEXT:    [[V1:%.*]] = select i1 [[ARG0]], i8 0, i8 8
-; CHECK-NEXT:    [[V2:%.*]] = or disjoint i8 [[V1]], [[V0]]
-; CHECK-NEXT:    [[V3:%.*]] = or disjoint i8 [[V2]], 16
+; CHECK-NEXT:    [[V3:%.*]] = select i1 [[ARG0:%.*]], i8 17, i8 24
 ; CHECK-NEXT:    ret i8 [[V3]]
 ;
   %v0 = zext i1 %arg0 to i8
@@ -433,10 +430,7 @@ define i8 @commonArgWithOr1(i1 %arg0) {
 
 define i8 @commonArgWithOr2(i1 %arg0) {
 ; CHECK-LABEL: @commonArgWithOr2(
-; CHECK-NEXT:    [[V0:%.*]] = zext i1 [[ARG0:%.*]] to i8
-; CHECK-NEXT:    [[V1:%.*]] = select i1 [[ARG0]], i8 5, i8 42
-; CHECK-NEXT:    [[V2:%.*]] = or i8 [[V1]], [[V0]]
-; CHECK-NEXT:    [[V3:%.*]] = or disjoint i8 [[V2]], 16
+; CHECK-NEXT:    [[V3:%.*]] = select i1 [[ARG0:%.*]], i8 21, i8 58
 ; CHECK-NEXT:    ret i8 [[V3]]
 ;
   %v0 = zext i1 %arg0 to i8
@@ -496,10 +490,7 @@ define i8 @commonArgWithAnd3(i1 %arg0) {
 
 define i8 @commonArgWithXor0(i1 %arg0) {
 ; CHECK-LABEL: @commonArgWithXor0(
-; CHECK-NEXT:    [[V0:%.*]] = zext i1 [[ARG0:%.*]] to i8
-; CHECK-NEXT:    [[V1:%.*]] = select i1 [[ARG0]], i8 0, i8 8
-; CHECK-NEXT:    [[V2:%.*]] = or disjoint i8 [[V1]], [[V0]]
-; CHECK-NEXT:    [[V3:%.*]] = or disjoint i8 [[V2]], 16
+; CHECK-NEXT:    [[V3:%.*]] = select i1 [[ARG0:%.*]], i8 17, i8 24
 ; CHECK-NEXT:    ret i8 [[V3]]
 ;
   %v0 = zext i1 %arg0 to i8
@@ -511,9 +502,7 @@ define i8 @commonArgWithXor0(i1 %arg0) {
 
 define i8 @commonArgWithXor1(i1 %arg0) {
 ; CHECK-LABEL: @commonArgWithXor1(
-; CHECK-NEXT:    [[V0:%.*]] = zext i1 [[ARG0:%.*]] to i8
-; CHECK-NEXT:    [[V1:%.*]] = select i1 [[ARG0]], i8 9, i8 1
-; CHECK-NEXT:    [[V2:%.*]] = xor i8 [[V1]], [[V0]]
+; CHECK-NEXT:    [[V2:%.*]] = select i1 [[ARG0:%.*]], i8 8, i8 1
 ; CHECK-NEXT:    ret i8 [[V2]]
 ;
   %v0 = zext i1 %arg0 to i8
@@ -524,10 +513,7 @@ define i8 @commonArgWithXor1(i1 %arg0) {
 
 define i8 @commonArgWithXor2(i1 %arg0) {
 ; CHECK-LABEL: @commonArgWithXor2(
-; CHECK-NEXT:    [[V0:%.*]] = zext i1 [[ARG0:%.*]] to i8
-; CHECK-NEXT:    [[V1:%.*]] = select i1 [[ARG0]], i8 1, i8 7
-; CHECK-NEXT:    [[V2:%.*]] = xor i8 [[V1]], [[V0]]
-; CHECK-NEXT:    [[V3:%.*]] = or disjoint i8 [[V2]], 16
+; CHECK-NEXT:    [[V3:%.*]] = select i1 [[ARG0:%.*]], i8 16, i8 23
 ; CHECK-NEXT:    ret i8 [[V3]]
 ;
   %v0 = zext i1 %arg0 to i8
@@ -539,10 +525,7 @@ define i8 @commonArgWithXor2(i1 %arg0) {
 
 define i8 @commonArgWithXor3(i1 %arg0) {
 ; CHECK-LABEL: @commonArgWithXor3(
-; CHECK-NEXT:    [[V0:%.*]] = zext i1 [[ARG0:%.*]] to i8
-; CHECK-NEXT:    [[V1:%.*]] = select i1 [[ARG0]], i8 5, i8 45
-; CHECK-NEXT:    [[V2:%.*]] = xor i8 [[V1]], [[V0]]
-; CHECK-NEXT:    [[V3:%.*]] = or disjoint i8 [[V2]], 16
+; CHECK-NEXT:    [[V3:%.*]] = select i1 [[ARG0:%.*]], i8 20, i8 61
 ; CHECK-NEXT:    ret i8 [[V3]]
 ;
   %v0 = zext i1 %arg0 to i8