[llvm] Support indirect symbol replacement with GOTPCREL for x86_64 ELF

llvm/lib/Target/X86/X86TargetObjectFile.cpp

@@ -56,3 +56,13 @@ const MCExpr *X86ELFTargetObjectFile::getDebugThreadLocalSymbol(
     const MCSymbol *Sym) const {
   return MCSymbolRefExpr::create(Sym, MCSymbolRefExpr::VK_DTPOFF, getContext());
 }
+
+const MCExpr *X86ELFTargetObjectFile::getIndirectSymViaGOTPCRel(
+    const GlobalValue *GV, const MCSymbol *Sym, const MCValue &MV,
+    int64_t Offset, MachineModuleInfo *MMI, MCStreamer &Streamer) const {
+  int64_t FinalOffset = Offset + MV.getConstant();
+  const MCExpr *Res =
+      MCSymbolRefExpr::create(Sym, MCSymbolRefExpr::VK_GOTPCREL, getContext());
+  const MCExpr *Off = MCConstantExpr::create(FinalOffset, getContext());
+  return MCBinaryExpr::createAdd(Res, Off, getContext());
+}

llvm/lib/Target/X86/X86TargetObjectFile.h

@@ -42,9 +42,16 @@ namespace llvm {
   public:
     X86ELFTargetObjectFile() {
       PLTRelativeVariantKind = MCSymbolRefExpr::VK_PLT;
+      SupportIndirectSymViaGOTPCRel = true;
     }
     /// Describe a TLS variable address within debug info.
     const MCExpr *getDebugThreadLocalSymbol(const MCSymbol *Sym) const override;
+
+    const MCExpr *
+    getIndirectSymViaGOTPCRel(const GlobalValue *GV, const MCSymbol *Sym,
+                              const MCValue &MV, int64_t Offset,
+                              MachineModuleInfo *MMI,
+                              MCStreamer &Streamer) const override;
   };
 
 } // end namespace llvm

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

@@ -0,0 +1,27 @@
+; RUN: llc %s -mtriple=x86_64-unknown-fuchsia  -o - | FileCheck %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
+@vtable_with_offset = dso_local unnamed_addr constant [2 x i32] [i32 0, i32 trunc (i64 sub (i64 ptrtoint (ptr @rtti.proxy to i64), i64 ptrtoint (ptr @vtable_with_offset to i64)) to i32)], align 4
+@vtable_with_negative_offset = dso_local unnamed_addr constant [2 x i32] [
+  i32 trunc (
+    i64 sub (
+      i64 ptrtoint (ptr @rtti.proxy to i64),
+      i64 ptrtoint (ptr getelementptr inbounds ([2 x i32], ptr @vtable_with_negative_offset, i32 0, i32 1) to i64)
+    )
+    to i32),
+  i32 0
+], align 4
+@rtti = external global i8, align 8
+@rtti.proxy = linkonce_odr hidden unnamed_addr constant ptr @rtti
+
+; CHECK-NOT: rtti.proxy
+; CHECK-LABEL: vtable:
+; CHECK-NEXT:    .{{word|long}}   rtti@GOTPCREL+0{{$}}
+
+; CHECK-LABEL: vtable_with_offset:
+; CHECK-NEXT:    .{{word|long}}   0
+; CHECK-NEXT:    .{{word|long}}   rtti@GOTPCREL+4{{$}}
+
+; CHECK-LABEL: vtable_with_negative_offset:
+; CHECK-NEXT:    .{{word|long}}   rtti@GOTPCREL-4{{$}}
+; CHECK-NEXT:    .{{word|long}}   0