[X86] Fix RTTI proxy emission for 32-bit

llvm/lib/Target/X86/X86TargetMachine.cpp

@@ -113,6 +113,9 @@ static std::unique_ptr<TargetLoweringObjectFile> createTLOF(const Triple &TT) {
 
   if (TT.isOSBinFormatCOFF())
     return std::make_unique<TargetLoweringObjectFileCOFF>();
+
+  if (TT.getArch() == Triple::x86_64)
+    return std::make_unique<X86_64ELFTargetObjectFile>();
   return std::make_unique<X86ELFTargetObjectFile>();
 }
 

llvm/lib/Target/X86/X86TargetObjectFile.cpp

@@ -57,7 +57,7 @@ const MCExpr *X86ELFTargetObjectFile::getDebugThreadLocalSymbol(
   return MCSymbolRefExpr::create(Sym, MCSymbolRefExpr::VK_DTPOFF, getContext());
 }
 
-const MCExpr *X86ELFTargetObjectFile::getIndirectSymViaGOTPCRel(
+const MCExpr *X86_64ELFTargetObjectFile::getIndirectSymViaGOTPCRel(
     const GlobalValue *GV, const MCSymbol *Sym, const MCValue &MV,
     int64_t Offset, MachineModuleInfo *MMI, MCStreamer &Streamer) const {
   int64_t FinalOffset = Offset + MV.getConstant();

llvm/lib/Target/X86/X86TargetObjectFile.h

@@ -36,16 +36,22 @@ namespace llvm {
                                             MCStreamer &Streamer) const override;
   };
 
-  /// This implementation is used for X86 ELF targets that don't
-  /// have a further specialization.
+  /// This implementation is used for X86 ELF targets that don't have a further
+  /// specialization (and as a base class for X86_64, which does).
   class X86ELFTargetObjectFile : public TargetLoweringObjectFileELF {
   public:
     X86ELFTargetObjectFile() {
       PLTRelativeVariantKind = MCSymbolRefExpr::VK_PLT;
-      SupportIndirectSymViaGOTPCRel = true;
     }
     /// Describe a TLS variable address within debug info.
     const MCExpr *getDebugThreadLocalSymbol(const MCSymbol *Sym) const override;
+  };
+
+  /// This implementation is used for X86_64 ELF targets, and defers to
+  /// X86ELFTargetObjectFile for commonalities with 32-bit targets.
+  class X86_64ELFTargetObjectFile : public X86ELFTargetObjectFile {
+  public:
+    X86_64ELFTargetObjectFile() { SupportIndirectSymViaGOTPCRel = true; }
 
     const MCExpr *
     getIndirectSymViaGOTPCRel(const GlobalValue *GV, const MCSymbol *Sym,

llvm/test/MC/ELF/rtti-proxy-i686.ll

@@ -0,0 +1,20 @@
+; REQUIRES: x86-registered-target
+
+;; Validate that we produce RTTI proxies for 32-bit x86.
+; RUN: llc %s -mtriple=i686-elf -o - | FileCheck %s
+
+;; Validate that we produce a valid object file.
+; RUN: llc %s -mtriple=i686-elf --filetype=obj -o %t.o
+; RUN: llvm-readobj --relocs %t.o | FileCheck --check-prefix=RELOCS %s
+
+@vtable = dso_local unnamed_addr constant i32 trunc (i64 sub (i64 ptrtoint (ptr @rtti.proxy to i64), i64 ptrtoint (ptr @vtable to i64)) to i32), align 4
+@rtti = external global i8, align 8
+@rtti.proxy = linkonce_odr hidden unnamed_addr constant ptr @rtti
+
+; CHECK-LABEL: vtable:
+; CHECK-NEXT:    .long   rtti.proxy-vtable
+
+; CHECK-LABEL: rtti.proxy:
+; CHECK-NEXT:    .long   rtti
+
+; RELOCS: R_386_32 rtti