[clang] [llvm] [X86][AsmParser] Fix MS inline asm label mismatch with offset operator (PR #199552)

[via cfe-commits]

https://github.com/sonyps5201314 created https://github.com/llvm/llvm-project/pull/199552

When using the 'offset' operator to reference an inline asm label in MSVC-style inline assembly, the label reference was missing the PrivateLabelPrefix (e.g., 'L' on COFF targets). This caused a symbol name mismatch between the label definition and its reference:

- Label definition (via AOK_Label rewrite): L__MSASMLABEL_.0__name
- Offset reference (no rewrite): __MSASMLABEL_.0__name

This mismatch resulted in an 'undefined symbol' linker error when using lld-link on Windows.

The fix prepends PrivateLabelPrefix to the internal label name when parsing the offset operator, matching what AOK_Label does for label definitions and non-offset references.

for fix https://github.com/llvm/llvm-project/issues/132863

>From dce9fef3f39f3de1ef9b9b27e4270c5bf080d678 Mon Sep 17 00:00:00 2001
From: sonyps5201314 <sonyps5201314 at gmail.com>
Date: Tue, 26 May 2026 00:31:02 +0800
Subject: [PATCH] [X86][AsmParser] Fix MS inline asm label mismatch with offset
 operator

When using the 'offset' operator to reference an inline asm label in
MSVC-style inline assembly, the label reference was missing the
PrivateLabelPrefix (e.g., 'L' on COFF targets). This caused a symbol
name mismatch between the label definition and its reference:

- Label definition (via AOK_Label rewrite): L__MSASMLABEL_.0__name
- Offset reference (no rewrite): __MSASMLABEL_.0__name

This mismatch resulted in an 'undefined symbol' linker error when
using lld-link on Windows.

The fix prepends PrivateLabelPrefix to the internal label name when
parsing the offset operator, matching what AOK_Label does for label
definitions and non-offset references.
---
 clang/test/CodeGen/ms-inline-asm.c             | 14 ++++++++++++++
 llvm/lib/Target/X86/AsmParser/X86AsmParser.cpp | 10 ++++++++--
 2 files changed, 22 insertions(+), 2 deletions(-)

diff --git a/clang/test/CodeGen/ms-inline-asm.c b/clang/test/CodeGen/ms-inline-asm.c
index c3eef9a23e166..2cf3cb3ce74a2 100644
--- a/clang/test/CodeGen/ms-inline-asm.c
+++ b/clang/test/CodeGen/ms-inline-asm.c
@@ -789,6 +789,20 @@ int test_indirect_field(LARGE_INTEGER LargeInteger) {
 // CHECK-LABEL: define{{.*}} i32 @test_indirect_field(
 // CHECK: call i32 asm sideeffect inteldialect "mov eax, $1",
 
+// Test that 'offset' references to inline asm labels use the same
+// PrivateLabelPrefix as the label definition.
+void label_offset(void) {
+  __asm {
+    label_offset_target:
+    mov eax, offset label_offset_target
+  }
+  // CHECK-LABEL: define{{.*}} void @label_offset(
+  // CHECK: call void asm sideeffect inteldialect
+  // CHECK-SAME: {{.*}}__MSASMLABEL_.${:uid}__label_offset_target:
+  // CHECK-SAME: mov eax, offset {{.*}}__MSASMLABEL_.${:uid}__label_offset_target
+  // CHECK-SAME: "~{eax},~{dirflag},~{fpsr},~{flags}"()
+}
+
 // MS ASM containing labels must not be duplicated (PR23715).
 // CHECK: attributes [[ATTR1]] = {
 // CHECK-NOT: noduplicate
diff --git a/llvm/lib/Target/X86/AsmParser/X86AsmParser.cpp b/llvm/lib/Target/X86/AsmParser/X86AsmParser.cpp
index 1741efac3a8c7..942ee6bb07d28 100644
--- a/llvm/lib/Target/X86/AsmParser/X86AsmParser.cpp
+++ b/llvm/lib/Target/X86/AsmParser/X86AsmParser.cpp
@@ -2317,8 +2317,14 @@ bool X86AsmParser::ParseIntelInlineAsmIdentifier(
     if (!IsParsingOffsetOperator)
       InstInfo->AsmRewrites->emplace_back(AOK_Label, Loc, Identifier.size(),
                                           InternalName);
-    else
-      Identifier = InternalName;
+    else {
+      // When parsing the offset operator, we need to prepend
+      // PrivateLabelPrefix to match the AOK_Label rewrite at label definition.
+      StringRef Prefix = getContext().getAsmInfo().getPrivateLabelPrefix();
+      SmallString<128> PrefixedName;
+      (Twine(Prefix) + InternalName).toVector(PrefixedName);
+      Identifier = getContext().allocateString(PrefixedName);
+    }
   } else if (Info.isKind(InlineAsmIdentifierInfo::IK_EnumVal))
     return false;
   // Create the symbol reference.