[llvm] [X86] LowerAsmOperandForConstraint - ensure we treat L constraint immediates as signed constants (PR #171098)

[Simon Pilgrim via llvm-commits]

https://github.com/RKSimon created https://github.com/llvm/llvm-project/pull/171098

getTargetConstant no longer tolerates sign-extended values that can't be represented by the appropriate APInt bitwidth, which now defaults to unsigned behaviour.

Fixes #166058

>From b8a26dba1cde68ce4a3d08b2dd4fee9378211e47 Mon Sep 17 00:00:00 2001
From: Simon Pilgrim <llvm-dev at redking.me.uk>
Date: Mon, 8 Dec 2025 09:42:26 +0000
Subject: [PATCH] [X86] LowerAsmOperandForConstraint - ensure we treat L
 constraint immediates as signed constants

getTargetConstant no longer tolerates sign-extended values that can't be represented by the appropriate APInt bitwidth, which now defaults to unsigned behaviour.

Fixes #166058
---
 llvm/lib/Target/X86/X86ISelLowering.cpp |  4 ++--
 llvm/test/CodeGen/X86/pr166058.ll       | 15 +++++++++++++++
 2 files changed, 17 insertions(+), 2 deletions(-)
 create mode 100644 llvm/test/CodeGen/X86/pr166058.ll

diff --git a/llvm/lib/Target/X86/X86ISelLowering.cpp b/llvm/lib/Target/X86/X86ISelLowering.cpp
index d0ae75b2e6785..8f22f8c3618a6 100644
--- a/llvm/lib/Target/X86/X86ISelLowering.cpp
+++ b/llvm/lib/Target/X86/X86ISelLowering.cpp
@@ -61928,8 +61928,8 @@ void X86TargetLowering::LowerAsmOperandForConstraint(SDValue Op,
     if (auto *C = dyn_cast<ConstantSDNode>(Op)) {
       if (C->getZExtValue() == 0xff || C->getZExtValue() == 0xffff ||
           (Subtarget.is64Bit() && C->getZExtValue() == 0xffffffff)) {
-        Result = DAG.getTargetConstant(C->getSExtValue(), SDLoc(Op),
-                                       Op.getValueType());
+        Result = DAG.getSignedTargetConstant(C->getSExtValue(), SDLoc(Op),
+                                             Op.getValueType());
         break;
       }
     }
diff --git a/llvm/test/CodeGen/X86/pr166058.ll b/llvm/test/CodeGen/X86/pr166058.ll
new file mode 100644
index 0000000000000..2e0bb6036820f
--- /dev/null
+++ b/llvm/test/CodeGen/X86/pr166058.ll
@@ -0,0 +1,15 @@
+; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py UTC_ARGS: --version 6
+; RUN: llc -mtriple=x86_64-- | FileCheck %s
+
+ at out = global i32 0, align 4
+define void @bar() {
+; CHECK-LABEL: bar:
+; CHECK:       # %bb.0:
+; CHECK-NEXT:    movq out at GOTPCREL(%rip), %rax
+; CHECK-NEXT:    #APP
+; CHECK-NEXT:    addq $-1, (%rax)
+; CHECK-NEXT:    #NO_APP
+; CHECK-NEXT:    retq
+  call void asm "addq $1,$0", "=*m,L,~{dirflag},~{fpsr},~{flags}"(ptr elementtype(i32) @out, i32 -1)
+  ret void
+}