Reset PAL metadata when AMDGPU traget stream finishes

If the same stream object is used for multiple compiles, the PAL metadata from eariler compilations will leak into later one.  See GPUOpen-Drivers/llpc#882 for how this is happening in LLPC.

No tests were added because multiple compiles will have to happen using the same pass manager, and I do not see a setup for that on the LLVM side.  Let me know if there is a good way to test this.

Reviewed By: nhaehnle

Differential Revision: https://reviews.llvm.org/D85667

Author: s-perron

llvm/lib/Target/AMDGPU/MCTargetDesc/AMDGPUTargetStreamer.cpp

@@ -168,10 +168,15 @@ AMDGPUTargetAsmStreamer::AMDGPUTargetAsmStreamer(MCStreamer &S,
 
 // A hook for emitting stuff at the end.
 // We use it for emitting the accumulated PAL metadata as directives.
+// The PAL metadata is reset after it is emitted.
 void AMDGPUTargetAsmStreamer::finish() {
   std::string S;
   getPALMetadata()->toString(S);
   OS << S;
+
+  // Reset the pal metadata so its data will not affect a compilation that
+  // reuses this object.
+  getPALMetadata()->reset();
 }
 
 void AMDGPUTargetAsmStreamer::EmitDirectiveAMDGCNTarget(StringRef Target) {
@@ -423,6 +428,7 @@ MCELFStreamer &AMDGPUTargetELFStreamer::getStreamer() {
 
 // A hook for emitting stuff at the end.
 // We use it for emitting the accumulated PAL metadata as a .note record.
+// The PAL metadata is reset after it is emitted.
 void AMDGPUTargetELFStreamer::finish() {
   std::string Blob;
   const char *Vendor = getPALMetadata()->getVendor();
@@ -432,6 +438,10 @@ void AMDGPUTargetELFStreamer::finish() {
     return;
   EmitNote(Vendor, MCConstantExpr::create(Blob.size(), getContext()), Type,
            [&](MCELFStreamer &OS) { OS.emitBytes(Blob); });
+
+  // Reset the pal metadata so its data will not affect a compilation that
+  // reuses this object.
+  getPALMetadata()->reset();
 }
 
 void AMDGPUTargetELFStreamer::EmitNote(

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

@@ -773,3 +773,9 @@ void AMDGPUPALMetadata::setLegacy() {
   BlobType = ELF::NT_AMD_AMDGPU_PAL_METADATA;
 }
 
+// Erase all PAL metadata.
+void AMDGPUPALMetadata::reset() {
+  MsgPackDoc.clear();
+  Registers = MsgPackDoc.getEmptyNode();
+  HwStages = MsgPackDoc.getEmptyNode();
+}

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

@@ -106,6 +106,9 @@ class AMDGPUPALMetadata {
   // Set legacy PAL metadata format.
   void setLegacy();
 
+  // Erase all PAL metadata.
+  void reset();
+
 private:
   // Return whether the blob type is legacy PAL metadata.
   bool isLegacy() const;