[llvm] [CodeGen][X86] Honor LargeEHEncoding when selecting x86-64 EH encoding (PR #210109)

[Farid Zakaria via llvm-commits]

https://github.com/fzakaria created https://github.com/llvm/llvm-project/pull/210109

Apply suggestion from https://github.com/llvm/llvm-project/pull/174508#discussion_r3589397222

On x86-64, select the exception-handling pointer encodings as if the Large code model were in use when MCOptions.LargeEHEncoding is set. This uses a case-scoped local (EHCM) rather than mutating the object file's code model, so only the EH encoding selection is affected as recommended by @jrtc27 

>From c0a0ac18cc0fbc5392f0069a334524e10da5054c Mon Sep 17 00:00:00 2001
From: Farid Zakaria <fmzakari at fb.com>
Date: Thu, 16 Jul 2026 09:42:24 -0700
Subject: [PATCH] [CodeGen][X86] Honor LargeEHEncoding when selecting x86-64 EH
 pointer encodings

On x86-64, select the exception-handling pointer encodings as if the
Large code model were in use when MCOptions.LargeEHEncoding is set. This
uses a case-scoped local (EHCM) rather than mutating the object file's
code model, so only the EH encoding selection is affected.
---
 .../CodeGen/TargetLoweringObjectFileImpl.cpp  | 22 +++++++++++--------
 1 file changed, 13 insertions(+), 9 deletions(-)

diff --git a/llvm/lib/CodeGen/TargetLoweringObjectFileImpl.cpp b/llvm/lib/CodeGen/TargetLoweringObjectFileImpl.cpp
index c7d07c1e40393..855db870f2a59 100644
--- a/llvm/lib/CodeGen/TargetLoweringObjectFileImpl.cpp
+++ b/llvm/lib/CodeGen/TargetLoweringObjectFileImpl.cpp
@@ -150,29 +150,33 @@ void TargetLoweringObjectFileELF::Initialize(MCContext &Ctx,
                               dwarf::DW_EH_PE_sdata4
                         : dwarf::DW_EH_PE_absptr;
     break;
-  case Triple::x86_64:
-    if (TgtM.Options.MCOptions.LargeEHEncoding)
-      CM = CodeModel::Large;
+  case Triple::x86_64: {
+    // The large EH encoding forces 64-bit-wide EH pointers regardless of the
+    // code model, so treat it like the Large code model when selecting
+    // encodings below.
+    CodeModel::Model EHCM =
+        TgtM.Options.MCOptions.LargeEHEncoding ? CodeModel::Large : CM;
     if (isPositionIndependent()) {
       PersonalityEncoding = dwarf::DW_EH_PE_indirect | dwarf::DW_EH_PE_pcrel |
-        ((CM == CodeModel::Small || CM == CodeModel::Medium)
+        ((EHCM == CodeModel::Small || EHCM == CodeModel::Medium)
          ? dwarf::DW_EH_PE_sdata4 : dwarf::DW_EH_PE_sdata8);
       LSDAEncoding = dwarf::DW_EH_PE_pcrel |
-        (CM == CodeModel::Small
+        (EHCM == CodeModel::Small
          ? dwarf::DW_EH_PE_sdata4 : dwarf::DW_EH_PE_sdata8);
       TTypeEncoding = dwarf::DW_EH_PE_indirect | dwarf::DW_EH_PE_pcrel |
-        ((CM == CodeModel::Small || CM == CodeModel::Medium)
+        ((EHCM == CodeModel::Small || EHCM == CodeModel::Medium)
          ? dwarf::DW_EH_PE_sdata4 : dwarf::DW_EH_PE_sdata8);
     } else {
       PersonalityEncoding =
-        (CM == CodeModel::Small || CM == CodeModel::Medium)
+        (EHCM == CodeModel::Small || EHCM == CodeModel::Medium)
         ? dwarf::DW_EH_PE_udata4 : dwarf::DW_EH_PE_absptr;
-      LSDAEncoding = (CM == CodeModel::Small)
+      LSDAEncoding = (EHCM == CodeModel::Small)
         ? dwarf::DW_EH_PE_udata4 : dwarf::DW_EH_PE_absptr;
-      TTypeEncoding = (CM == CodeModel::Small)
+      TTypeEncoding = (EHCM == CodeModel::Small)
         ? dwarf::DW_EH_PE_udata4 : dwarf::DW_EH_PE_absptr;
     }
     break;
+  }
   case Triple::hexagon:
     PersonalityEncoding = dwarf::DW_EH_PE_absptr;
     LSDAEncoding = dwarf::DW_EH_PE_absptr;