[llvm] [X86] Allow all legal integers to optimize smin with 0 (PR #151893)

[via llvm-commits]

https://github.com/AZero13 updated https://github.com/llvm/llvm-project/pull/151893

>From 821f39e0ccfdd844fc651841bfc10f7089cb18c8 Mon Sep 17 00:00:00 2001
From: AZero13 <gfunni234 at gmail.com>
Date: Sun, 3 Aug 2025 21:56:30 -0400
Subject: [PATCH] [X86] Allow all legal integers to have optimize smin and smax
 with 0

It makes no sense why it has to be limited to 32 and 64 bits.
---
 llvm/lib/Target/X86/X86ISelLowering.cpp   |  2 +-
 llvm/test/CodeGen/X86/select-smin-smax.ll | 73 +++++++++--------------
 2 files changed, 29 insertions(+), 46 deletions(-)

diff --git a/llvm/lib/Target/X86/X86ISelLowering.cpp b/llvm/lib/Target/X86/X86ISelLowering.cpp
index f81efdc6414aa..457e959134e25 100644
--- a/llvm/lib/Target/X86/X86ISelLowering.cpp
+++ b/llvm/lib/Target/X86/X86ISelLowering.cpp
@@ -25093,7 +25093,7 @@ SDValue X86TargetLowering::LowerSELECT(SDValue Op, SelectionDAG &DAG) const {
     } else if (SDValue R = LowerSELECTWithCmpZero(CmpOp0, Op1, Op2, CondCode,
                                                   DL, DAG, Subtarget)) {
       return R;
-    } else if ((VT == MVT::i32 || VT == MVT::i64) && isNullConstant(Op2) &&
+    } else if (VT.isScalarInteger() && isNullConstant(Op2) &&
                Cmp.getNode()->hasOneUse() && (CmpOp0 == Op1) &&
                ((CondCode == X86::COND_S) ||                    // smin(x, 0)
                 (CondCode == X86::COND_G && hasAndNot(Op1)))) { // smax(x, 0)
diff --git a/llvm/test/CodeGen/X86/select-smin-smax.ll b/llvm/test/CodeGen/X86/select-smin-smax.ll
index 513983ba54bcf..0b518c37b656c 100644
--- a/llvm/test/CodeGen/X86/select-smin-smax.ll
+++ b/llvm/test/CodeGen/X86/select-smin-smax.ll
@@ -50,31 +50,18 @@ define i8 @test_i8_smax(i8 %a) nounwind {
 define i8 @test_i8_smin(i8 %a) nounwind {
 ; X64-LABEL: test_i8_smin:
 ; X64:       # %bb.0:
-; X64-NEXT:    xorl %eax, %eax
-; X64-NEXT:    testb %dil, %dil
-; X64-NEXT:    cmovsl %edi, %eax
-; X64-NEXT:    # kill: def $al killed $al killed $eax
+; X64-NEXT:    movl %edi, %eax
+; X64-NEXT:    sarb $7, %al
+; X64-NEXT:    andb %dil, %al
 ; X64-NEXT:    retq
 ;
-; X86-BMI-LABEL: test_i8_smin:
-; X86-BMI:       # %bb.0:
-; X86-BMI-NEXT:    movl {{[0-9]+}}(%esp), %ecx
-; X86-BMI-NEXT:    xorl %eax, %eax
-; X86-BMI-NEXT:    testb %cl, %cl
-; X86-BMI-NEXT:    cmovsl %ecx, %eax
-; X86-BMI-NEXT:    # kill: def $al killed $al killed $eax
-; X86-BMI-NEXT:    retl
-;
-; X86-NOBMI-LABEL: test_i8_smin:
-; X86-NOBMI:       # %bb.0:
-; X86-NOBMI-NEXT:    movzbl {{[0-9]+}}(%esp), %eax
-; X86-NOBMI-NEXT:    testb %al, %al
-; X86-NOBMI-NEXT:    js .LBB1_2
-; X86-NOBMI-NEXT:  # %bb.1:
-; X86-NOBMI-NEXT:    xorl %eax, %eax
-; X86-NOBMI-NEXT:  .LBB1_2:
-; X86-NOBMI-NEXT:    # kill: def $al killed $al killed $eax
-; X86-NOBMI-NEXT:    retl
+; X86-LABEL: test_i8_smin:
+; X86:       # %bb.0:
+; X86-NEXT:    movzbl {{[0-9]+}}(%esp), %ecx
+; X86-NEXT:    movl %ecx, %eax
+; X86-NEXT:    sarb $7, %al
+; X86-NEXT:    andb %cl, %al
+; X86-NEXT:    retl
   %r = call i8 @llvm.smin.i8(i8 %a, i8 0)
   ret i8 %r
 }
@@ -112,33 +99,29 @@ define i16 @test_i16_smax(i16 %a) nounwind {
 }
 
 define i16 @test_i16_smin(i16 %a) nounwind {
+; CHECK-LABEL: test_i16_smin:
+; CHECK:       # %bb.0:
+; CHECK-NEXT:    movswl %di, %eax
+; CHECK-NEXT:    sarl $15, %eax
+; CHECK-NEXT:    andl %edi, %eax
+; CHECK-NEXT:    # kill: def $ax killed $ax killed $eax
+; CHECK-NEXT:    retq
 ; X64-LABEL: test_i16_smin:
 ; X64:       # %bb.0:
-; X64-NEXT:    xorl %eax, %eax
-; X64-NEXT:    testw %di, %di
-; X64-NEXT:    cmovsl %edi, %eax
+; X64-NEXT:    movswl %di, %eax
+; X64-NEXT:    sarl $15, %eax
+; X64-NEXT:    andl %edi, %eax
 ; X64-NEXT:    # kill: def $ax killed $ax killed $eax
 ; X64-NEXT:    retq
 ;
-; X86-BMI-LABEL: test_i16_smin:
-; X86-BMI:       # %bb.0:
-; X86-BMI-NEXT:    movl {{[0-9]+}}(%esp), %ecx
-; X86-BMI-NEXT:    xorl %eax, %eax
-; X86-BMI-NEXT:    testw %cx, %cx
-; X86-BMI-NEXT:    cmovsl %ecx, %eax
-; X86-BMI-NEXT:    # kill: def $ax killed $ax killed $eax
-; X86-BMI-NEXT:    retl
-;
-; X86-NOBMI-LABEL: test_i16_smin:
-; X86-NOBMI:       # %bb.0:
-; X86-NOBMI-NEXT:    movl {{[0-9]+}}(%esp), %eax
-; X86-NOBMI-NEXT:    testw %ax, %ax
-; X86-NOBMI-NEXT:    js .LBB3_2
-; X86-NOBMI-NEXT:  # %bb.1:
-; X86-NOBMI-NEXT:    xorl %eax, %eax
-; X86-NOBMI-NEXT:  .LBB3_2:
-; X86-NOBMI-NEXT:    # kill: def $ax killed $ax killed $eax
-; X86-NOBMI-NEXT:    retl
+; X86-LABEL: test_i16_smin:
+; X86:       # %bb.0:
+; X86-NEXT:    movswl {{[0-9]+}}(%esp), %ecx
+; X86-NEXT:    movl %ecx, %eax
+; X86-NEXT:    shrl $15, %eax
+; X86-NEXT:    andl %ecx, %eax
+; X86-NEXT:    # kill: def $ax killed $ax killed $eax
+; X86-NEXT:    retl
   %r = call i16 @llvm.smin.i16(i16 %a, i16 0)
   ret i16 %r
 }