[AMDGPU] Do not generate spurious PAL metadata

[tpr]

Summary

My previous fix rL356591 "[AMDGPU] Added MsgPack format PAL metadata"
accidentally caused a spurious PAL metadata .note record to be emitted
for any AMDGPU output. That caused failures in the lld test
amdgpu-relocs.s. Fixed.

Change-Id: Ie04a2aaae890dcd490f22c89edf9913a77ce070e

[kzhuravl]

LGTM

[hliao]

LGTM

llvm/trunk/lib/Target/AMDGPU/Utils/AMDGPUPALMetadata.h

public:
   // Set PAL metadata from YAML text.
   bool setFromString(StringRef S);
 
   // Get .note record vendor name of metadata blob to be emitted.
   const char *getVendor() const;
 
   // Get .note record type of metadata blob to be emitted:
   // ELF::NT_AMD_AMDGPU_PAL_METADATA (legacy key=val format), or
-  // ELF::NT_AMD_AMDGPU_PAL_METADATA_MSGPACK or ELF::NT_AMDGPU_METADATA
-  // (MsgPack format).
+  // ELF::NT_AMDGPU_METADATA (MsgPack format), or
+  // 0 (no PAL metadata).
   unsigned getType() const;
 
   // Emit the accumulated PAL metadata as a binary blob.
   // This is called from AMDGPUTargetELFStreamer::Finish().
   void toBlob(unsigned Type, std::string &S);
 
   // Get the msgpack::Document for the PAL metadata.
   msgpack::Document *getMsgPackDoc() { return &MsgPackDoc; }

llvm/trunk/lib/Target/AMDGPU/Utils/AMDGPUPALMetadata.cpp

static const char *getRegisterName(unsigned RegNum) {
   for (; Entry->Num && Entry->Num != RegNum; ++Entry)
     ;
   return Entry->Name;
 }
 
 // Convert the accumulated PAL metadata into an asm directive.
 void AMDGPUPALMetadata::toString(std::string &String) {
   String.clear();
+  if (!BlobType)
+    return;
   raw_string_ostream Stream(String);
   if (isLegacy()) {
     if (MsgPackDoc.getRoot().getKind() == msgpack::Type::Nil)
       return;
     // Old linear reg=val format.
     Stream << '\t' << AMDGPU::PALMD::AssemblerDirective << ' ';
     auto Regs = getRegisters();
     for (auto I = Regs.begin(), E = Regs.end(); I != E; ++I) {
void AMDGPUPALMetadata::toString(std::string &String) {
   MsgPackDoc.toYAML(Stream);
   Stream << '\t' << AMDGPU::PALMD::AssemblerDirectiveEnd << '\n';
 
   // Restore original registers map.
   RegsObj = OrigRegs;
 }
 
 // Convert the accumulated PAL metadata into a binary blob for writing as
-// a .note record of the specified AMD type.
+// a .note record of the specified AMD type. Returns an empty blob if
+// there is no PAL metadata,
 void AMDGPUPALMetadata::toBlob(unsigned Type, std::string &Blob) {
   if (Type == ELF::NT_AMD_AMDGPU_PAL_METADATA)
     toLegacyBlob(Blob);
-  else
+  else if (Type)
     toMsgPackBlob(Blob);
 }
 
 void AMDGPUPALMetadata::toLegacyBlob(std::string &Blob) {
   Blob.clear();
   auto Registers = getRegisters();
   if (Registers.getMap().empty())
     return;

 
 // Get .note record vendor name of metadata blob to be emitted.
 const char *AMDGPUPALMetadata::getVendor() const {
   return isLegacy() ? ElfNote::NoteNameV2 : ElfNote::NoteNameV3;
 }
 
 // Get .note record type of metadata blob to be emitted:
 // ELF::NT_AMD_AMDGPU_PAL_METADATA (legacy key=val format), or
-// ELF::NT_AMDGPU_METADATA (MsgPack format).
+// ELF::NT_AMDGPU_METADATA (MsgPack format), or
+// 0 (no PAL metadata).
 unsigned AMDGPUPALMetadata::getType() const {
-  return BlobType ? BlobType : unsigned(ELF::NT_AMDGPU_METADATA);
+  return BlobType;
 }
 
 // Return whether the blob type is legacy PAL metadata.
 bool AMDGPUPALMetadata::isLegacy() const {
   return BlobType == ELF::NT_AMD_AMDGPU_PAL_METADATA;
 }
 
 // Set legacy PAL metadata format.
 void AMDGPUPALMetadata::setLegacy() {
   BlobType = ELF::NT_AMD_AMDGPU_PAL_METADATA;
 }
 

llvm/trunk/test/MC/AMDGPU/spurious-pal-metadata.s

+# RUN: llvm-mc -triple=amdgcn--amdhsa -mcpu=fiji %s | FileCheck %s --check-prefix=ASM
+# RUN: llvm-mc -filetype=obj -triple=amdgcn--amdhsa -mcpu=fiji %s -o %t.o
+# RUN: llvm-objdump -s %t.o | FileCheck %s --check-prefix=OBJDUMP
+
+# Check that we don't get spurious PAL metadata. 
+
+# ASM-NOT: pal_metadata
+# OBJDUMP-NOT: section .note