[PATCH] D121346: [Propeller] Encode address offsets of basic blocks relative to the end of the previous basic blocks.

[Rahman Lavaee via Phabricator via llvm-commits]

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Cleanup.


This is a resurrection of D106421 <https://reviews.llvm.org/D106421> with the change that it keeps backward-compatibility. This means decoding the previous version of `llvm_bb_address_map` will work. This is required as the profile mapping tool is not released with LLVM (AutoFDO). We add a version suffix (`.v#{version_number}`) to the section name which distinguishes it from the old version (which wouldn't have a version suffix).

Conceptually, the new encoding emits basic block offsets and sizes as label differences between each two consecutive basic block begin and end label. When decoding, offsets must be aggregated along with basic block sizes to calculate the final offsets of basic blocks relative to the function address.

This encoding uses smaller values compared to the existing one (offsets relative to function symbol).
Smaller values tend to occupy fewer bytes in ULEB128 encoding. As a result, we get about 25% reduction in the size of the bb-address-map section (from about 9MB to 7MB for the clang PGO binary).


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D121346

Files:
  llvm/lib/CodeGen/AsmPrinter/AsmPrinter.cpp
  llvm/lib/CodeGen/BasicBlockSections.cpp
  llvm/lib/MC/MCObjectFileInfo.cpp
  llvm/lib/Object/ELF.cpp
  llvm/test/CodeGen/X86/basic-block-sections-labels-empty-function.ll
  llvm/test/CodeGen/X86/basic-block-sections-labels-functions-sections.ll
  llvm/test/CodeGen/X86/basic-block-sections-labels.ll
  llvm/test/tools/llvm-readobj/ELF/bb-addr-map.test
  llvm/test/tools/obj2yaml/ELF/bb-addr-map.yaml
  llvm/unittests/Object/ELFObjectFileTest.cpp

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