[RemoveDIs] Read/write DbgRecords directly from/to bitcode (#83251)

If --write-experimental-debuginfo-iterators-to-bitcode is true (default false)
and --expermental-debuginfo-iterators is also true then the new debug info
format (non-instruction records) is written to bitcode directly.

Added the following records:

    FUNC_CODE_DEBUG_RECORD_LABEL
    FUNC_CODE_DEBUG_RECORD_VALUE
    FUNC_CODE_DEBUG_RECORD_DECLARE
    FUNC_CODE_DEBUG_RECORD_ASSIGN
    FUNC_CODE_DEBUG_RECORD_VALUE_SIMPLE

The last one has an abbrev in FUNCTION_BLOCK BLOCK_INFO. Incidentally, this uses
the last value available without widening the code-length for FUNCTION_BLOCK
from 4 to 5 bits.

Records are formatted as follows:

    All DbgRecord start with:
      1. DILocation

      FUNC_CODE_DEBUG_RECORD_LABEL
        2. DILabel

      DPValues then share common fields:
        2. DILocalVariable
        3. DIExpression

        FUNC_CODE_DEBUG_RECORD_VALUE
          4. Location Metadata

        FUNC_CODE_DEBUG_RECORD_DECLARE
          4. Location Metadata

        FUNC_CODE_DEBUG_RECORD_VALUE_SIMPLE
	  4. Location Value (single)

        FUNC_CODE_DEBUG_RECORD_ASSIGN
	  4. Location Metadata
	  5. DIAssignID
	  6. DIExpression (address)
	  7. Location Metadata (address)

Encoding the DILocation metadata reference directly appeared to yield smaller
bitcode files than encoding the operands seperately (as is done with instruction
DILocations).

FUNC_CODE_DEBUG_RECORD_VALUE_SIMPLE is by far the most common DbgRecord record
in optimized code (order of 5x-10x over other kinds). Unoptimized code should
only contain FUNC_CODE_DEBUG_RECORD_DECLARE.

1 files changed, 10 insertions, 10 deletions

diff --git a/llvm/lib/Bitcode/Writer/BitcodeWriterPass.cpp b/llvm/lib/Bitcode/Writer/BitcodeWriterPass.cpp
index 0eb9c246f2a9..de2396f31f66 100644
--- a/llvm/lib/Bitcode/Writer/BitcodeWriterPass.cpp
+++ b/llvm/lib/Bitcode/Writer/BitcodeWriterPass.cpp
@@ -18,11 +18,12 @@
 #include "llvm/Pass.h"
 using namespace llvm;
 
+extern bool WriteNewDbgInfoFormatToBitcode;
+
 PreservedAnalyses BitcodeWriterPass::run(Module &M, ModuleAnalysisManager &AM) {
-  // RemoveDIs: there's no bitcode representation of the DbgRecord debug-info,
-  // convert to dbg.values before writing out.
-  bool IsNewDbgInfoFormat = M.IsNewDbgInfoFormat;
-  if (IsNewDbgInfoFormat)
+  bool ConvertToOldDbgFormatForWrite =
+      M.IsNewDbgInfoFormat && !WriteNewDbgInfoFormatToBitcode;
+  if (ConvertToOldDbgFormatForWrite)
     M.convertFromNewDbgValues();
 
   const ModuleSummaryIndex *Index =
@@ -30,7 +31,7 @@ PreservedAnalyses BitcodeWriterPass::run(Module &M, ModuleAnalysisManager &AM) {
                        : nullptr;
   WriteBitcodeToFile(M, OS, ShouldPreserveUseListOrder, Index, EmitModuleHash);
 
-  if (IsNewDbgInfoFormat)
+  if (ConvertToOldDbgFormatForWrite)
     M.convertToNewDbgValues();
 
   return PreservedAnalyses::all();
@@ -56,16 +57,15 @@ namespace {
     StringRef getPassName() const override { return "Bitcode Writer"; }
 
     bool runOnModule(Module &M) override {
-      // RemoveDIs: there's no bitcode representation of the DbgRecord
-      // debug-info, convert to dbg.values before writing out.
-      bool IsNewDbgInfoFormat = M.IsNewDbgInfoFormat;
-      if (IsNewDbgInfoFormat)
+      bool ConvertToOldDbgFormatForWrite =
+          M.IsNewDbgInfoFormat && !WriteNewDbgInfoFormatToBitcode;
+      if (ConvertToOldDbgFormatForWrite)
         M.convertFromNewDbgValues();
 
       WriteBitcodeToFile(M, OS, ShouldPreserveUseListOrder, /*Index=*/nullptr,
                          /*EmitModuleHash=*/false);
 
-      if (IsNewDbgInfoFormat)
+      if (ConvertToOldDbgFormatForWrite)
         M.convertToNewDbgValues();
       return false;
     }