[all-commits] [llvm/llvm-project] d6d3d9: [RemoveDIs] Read/write DbgRecords directly from/to...

[Orlando Cazalet-Hyams via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: d6d3d96b654012d72ad170d272cb2fe2c8def90d
      https://github.com/llvm/llvm-project/commit/d6d3d96b654012d72ad170d272cb2fe2c8def90d
  Author: Orlando Cazalet-Hyams <orlando.hyams at sony.com>
  Date:   2024-03-15 (Fri, 15 Mar 2024)

  Changed paths:
    M llvm/include/llvm/Bitcode/LLVMBitCodes.h
    M llvm/lib/Bitcode/Reader/BitcodeAnalyzer.cpp
    M llvm/lib/Bitcode/Reader/BitcodeReader.cpp
    M llvm/lib/Bitcode/Writer/BitcodeWriter.cpp
    M llvm/lib/Bitcode/Writer/BitcodeWriterPass.cpp
    M llvm/lib/Bitcode/Writer/ValueEnumerator.cpp
    M llvm/lib/IR/BasicBlock.cpp
    M llvm/lib/Linker/IRMover.cpp
    M llvm/lib/Transforms/IPO/ThinLTOBitcodeWriter.cpp
    A llvm/test/Bitcode/dbg-record-roundtrip.ll
    M llvm/tools/llvm-as/llvm-as.cpp
    M llvm/tools/verify-uselistorder/verify-uselistorder.cpp

  Log Message:
  -----------
  [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.



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