[AMDGPU] Print DWARF register numbers in AMDGPUInstPrinter

[scott.linder]

Summary

Explanation is in a comment in the diff, but essentially printing a
physical register name here is ambiguous. Until we can implement
printing a DWARF register name here just use the encoding directly.

[scott.linder]

This should unblock @RamNalamothu working on the wave32 DWARF mapping.

[t-tye]

Minor suggestion in comment.

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

37

v0 would be a better example than s0 as the vector registers have wave32 and wave64 DWARF versions, but the scalar registers are the same for both modes.

[scott.linder]

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

37

Thank you for the catch! That was my intention, I just used the wrong prefix. Updated in the final diff.

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

 #include "llvm/Support/MathExtras.h"
 #include "llvm/Support/raw_ostream.h"
 #include <cassert>
 
 using namespace llvm;
 using namespace llvm::AMDGPU;
 
 void AMDGPUInstPrinter::printRegName(raw_ostream &OS, unsigned RegNo) const {
-  OS << getRegisterName(RegNo);
+  // FIXME: The current implementation of
+  // AsmParser::parseRegisterOrRegisterNumber in MC implies we either emit this
+  // as an integer or we provide a name which represents a physical register.
+  // For CFI instructions we really want to emit a name for the DWARF register
+  // instead, because there may be multiple DWARF registers corresponding to a
+  // single physical register. One case where this problem manifests is with
+  // wave32/wave64 where using the physical register name is ambiguous: if we
+  // write e.g. `.cfi_undefined v0` we lose information about the wavefront
+  // size which we need to encode the register in the final DWARF. Ideally we
+  // would extend MC to support parsing DWARF register names so we could do
+  // something like `.cfi_undefined dwarf_wave32_v0`. For now we just live with
+  // non-pretty DWARF register names in assembly text.
+  OS << RegNo;
 }
 
 void AMDGPUInstPrinter::printInst(const MCInst *MI, uint64_t Address,
                                   StringRef Annot, const MCSubtargetInfo &STI,
                                   raw_ostream &OS) {
   OS.flush();
   printInstruction(MI, Address, STI, OS);
   printAnnotation(OS, Annot);

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

AMDGPUMCAsmInfo::AMDGPUMCAsmInfo(const Triple &TT,
 
   //===--- Global Variable Emission Directives --------------------------===//
   HasAggressiveSymbolFolding = true;
   COMMDirectiveAlignmentIsInBytes = false;
   HasNoDeadStrip = true;
   WeakRefDirective = ".weakref\t";
   //===--- Dwarf Emission Directives -----------------------------------===//
   SupportsDebugInformation = true;
+  DwarfRegNumForCFI = true;
 }
 
 bool AMDGPUMCAsmInfo::shouldOmitSectionDirective(StringRef SectionName) const {
   return SectionName == ".hsatext" || SectionName == ".hsadata_global_agent" ||
          SectionName == ".hsadata_global_program" ||
          SectionName == ".hsarodata_readonly_agent" ||
          MCAsmInfo::shouldOmitSectionDirective(SectionName);
 }

llvm/test/DebugInfo/AMDGPU/print-reg-name.s

 ; RUN: llvm-mc -triple=amdgcn-amd-amdhsa -mcpu=gfx900 -filetype=asm %s | FileCheck %s
 
-; Check that we can print symbolic register operands in CFI instructions.
+; FIXME: Currently we can't print register names in CFI directives
+; without extending MC to support DWARF register names that are distinct
+; from physical register names.
 
 .text
 f:
 .cfi_startproc
-; CHECK: .cfi_undefined s0
-.cfi_undefined s0
+; CHECK: .cfi_undefined 2560
+.cfi_undefined 2560
+; FIXME: Until we implement a distinct set of DWARF register names we
+; will continue to parse physical registers and pick an arbitrary encoding.
+; CHECK: .cfi_undefined 2560
+.cfi_undefined v0
 .cfi_endproc

llvm/test/DebugInfo/AMDGPU/register-mapping.s

-; RUN: llvm-mc -triple=amdgcn-amd-amdhsa -mcpu=gfx1010 -filetype=obj %s | llvm-dwarfdump -debug-frame - | FileCheck %s
-
-; Check that we implement the DWARF register mapping.
-
-.text
-f:
-.cfi_startproc
-; CHECK: CIE
-; CHECK: Return address column: 16
-
-; CHECK: FDE
-; CHECK: DW_CFA_undefined: reg16
-.cfi_undefined pc
-; CHECK: DW_CFA_undefined: reg17
-.cfi_undefined exec
-
-; CHECK: DW_CFA_undefined: reg32
-.cfi_undefined s0
-; CHECK: DW_CFA_undefined: reg95
-.cfi_undefined s63
-
-; CHECK: DW_CFA_undefined: reg1088
-.cfi_undefined s64
-; CHECK: DW_CFA_undefined: reg1129
-.cfi_undefined s105
-
-; CHECK: DW_CFA_undefined: reg2560
-.cfi_undefined v0
-; CHECK: DW_CFA_undefined: reg2815
-.cfi_undefined v255
-
-; CHECK: DW_CFA_undefined: reg3072
-.cfi_undefined a0
-; CHECK: DW_CFA_undefined: reg3327
-.cfi_undefined a255
-
-.cfi_endproc