[MS][ARM64]: Hoist __ImageBase handling into TargetLoweringObjectFileCOFF::lowerRelativeReference, so that all COFF targets get this.

[arm-chrjan01]

Summary

Hoist __ImageBase handling into TargetLoweringObjectFileCOFF::lowerRelativeReference, so that all COFF targets get this. Do the same for getSectionForConstant.

[rnk]

lib/Target/AArch64/AArch64TargetObjectFile.cpp

82

Rather than duplicate this, I think we should hoist __ImageBase handling into TargetLoweringObjectFileCOFF::lowerRelativeReference, so that all COFF targets get this.

Also, do you think you'll need to do the same for getSectionForConstant?

[arm-chrjan01]

Refactored as per Reid's comment.

[rnk]

Needs a test. I think you can copy llvm/test/MC/COFF/ir-to-imgrel.ll to llvm/test/MC/AArch64/ and modify it accordingly. The test is kind of in the wrong location, though. It should really be in llvm/test/CodeGen/(X86|AArch64), since it's an llc test.

include/llvm/CodeGen/TargetLoweringObjectFileImpl.h

167–168 ↗

(On Diff #150108)

This doesn't look like something clang-format would produce, consider running git clang-format to reformat the lines touched in the patch.

[arm-chrjan01]

Added test case. Fixed formatting in TargetLoweringObjectFileImpl.h.

[rnk]

lgtm

[arm-chrjan01]

Thank you for reviewing Reid. Please could you commit the change for me as I don't have commit rights.

lib/Target/AArch64/AArch64TargetMachine.cpp

 }
 
 //===----------------------------------------------------------------------===//
 // AArch64 Lowering public interface.
 //===----------------------------------------------------------------------===//
 static std::unique_ptr<TargetLoweringObjectFile> createTLOF(const Triple &TT) {
   if (TT.isOSBinFormatMachO())
     return llvm::make_unique<AArch64_MachoTargetObjectFile>();
+  if (TT.isKnownWindowsMSVCEnvironment() || TT.isWindowsCoreCLREnvironment())
+    return llvm::make_unique<AArch64_WindowsTargetObjectFile>();
   if (TT.isOSBinFormatCOFF())
     return llvm::make_unique<AArch64_COFFTargetObjectFile>();
 
   return llvm::make_unique<AArch64_ELFTargetObjectFile>();
 }
 
 // Helper function to build a DataLayout string
 static std::string computeDataLayout(const Triple &TT,

lib/Target/AArch64/AArch64TargetObjectFile.h

public:
 
   void getNameWithPrefix(SmallVectorImpl<char> &OutName, const GlobalValue *GV,
                          const TargetMachine &TM) const override;
 };
 
 /// This implementation is used for AArch64 COFF targets.
 class AArch64_COFFTargetObjectFile : public TargetLoweringObjectFileCOFF {};
 
+/// This implementation is used for Windows targets on aarch64.
+class AArch64_WindowsTargetObjectFile : public AArch64_COFFTargetObjectFile {
+public:
+    const MCExpr *
+    lowerRelativeReference(const GlobalValue *LHS, const GlobalValue *RHS,
+                           const TargetMachine &TM) const override;
+};
+
 } // end namespace llvm
 
 #endif

lib/Target/AArch64/AArch64TargetObjectFile.cpp

 
 void AArch64_MachoTargetObjectFile::getNameWithPrefix(
     SmallVectorImpl<char> &OutName, const GlobalValue *GV,
     const TargetMachine &TM) const {
   // AArch64 does not use section-relative relocations so any global symbol must
   // be accessed via at least a linker-private symbol.
   getMangler().getNameWithPrefix(OutName, GV, /* CannotUsePrivateLabel */ true);
 }
+
+const MCExpr *AArch64_WindowsTargetObjectFile::lowerRelativeReference(
+    const GlobalValue *LHS, const GlobalValue *RHS,
+    const TargetMachine &TM) const {
+  // Our symbols should exist in address space zero, cowardly no-op if
+  // otherwise.
+  if (LHS->getType()->getPointerAddressSpace() != 0 ||
+      RHS->getType()->getPointerAddressSpace() != 0)
+    return nullptr;
+
+  // Both ptrtoint instructions must wrap global objects:
+  // - Only global variables are eligible for image relative relocations.
+  // - The subtrahend refers to the special symbol __ImageBase, a GlobalVariable.
+  // We expect __ImageBase to be a global variable without a section, externally
+  // defined.
+  //
+  // It should look something like this: @__ImageBase = external constant i8
+  if (!isa<GlobalObject>(LHS) || !isa<GlobalVariable>(RHS) ||
+      LHS->isThreadLocal() || RHS->isThreadLocal() ||
+      RHS->getName() != "__ImageBase" || !RHS->hasExternalLinkage() ||
+      cast<GlobalVariable>(RHS)->hasInitializer() || RHS->hasSection())
+    return nullptr;
+
+  return MCSymbolRefExpr::create(TM.getSymbol(LHS),
+                                 MCSymbolRefExpr::VK_COFF_IMGREL32,
+                                 getContext());
+}