[PATCH] D39747: [globalisel][tablegen] Generate rule coverage and use it to identify untested rules

[Daniel Sanders via Phabricator via llvm-commits]

dsanders created this revision.
Herald added subscribers: igorb, javed.absar, kristof.beyls, mgorny, nhaehnle, arsenm.

This patch adds a LLVM_ENABLE_GISEL_COV which, like LLVM_ENABLE_DAGISEL_COV,
causes TableGen to instrument the generated table to collect rule coverage
information. However, LLVM_ENABLE_GISEL_COV goes a bit further than
LLVM_ENABLE_DAGISEL_COV. The information is written to files
(${CMAKE_BINARY_DIR}/gisel-coverage-* by default). These files can then be
concatenated into ${LLVM_GISEL_COV_PREFIX}-all after which TableGen will
read this information and use it to emit warnings about untested rules.

This technique could also be used by SelectionDAG and can be further
extended to detect hot rules and give them priority over colder rules.

Usage:

- Enable LLVM_ENABLE_GISEL_COV in CMake
- Build the compiler and run some tests
- cat gisel-coverage-[0-9]* > gisel-coverage-all
- Delete lib/Target/*/*GenGlobalISel.inc*
- Build the compiler

Known issues:

- ${LLVM_GISEL_COV_PREFIX}-all must be generated as a manual step due to a lack of a portable 'cat' command. It should be the concatenation of all ${LLVM_GISEL_COV_PREFIX}-[0-9]* files.
- There's no mechanism to discard coverage information when the ruleset changes

Depends on https://reviews.llvm.org/D39742


https://reviews.llvm.org/D39747

Files:
  CMakeLists.txt
  cmake/modules/TableGen.cmake
  include/llvm/CodeGen/GlobalISel/InstructionSelector.h
  include/llvm/CodeGen/GlobalISel/InstructionSelectorImpl.h
  include/llvm/Config/config.h.cmake
  include/llvm/Support/CodeGenCoverage.h
  lib/CodeGen/GlobalISel/InstructionSelect.cpp
  lib/Support/CMakeLists.txt
  lib/Support/CodeGenCoverage.cpp
  lib/Target/AArch64/AArch64InstructionSelector.cpp
  lib/Target/AMDGPU/AMDGPUInstructionSelector.cpp
  lib/Target/AMDGPU/AMDGPUInstructionSelector.h
  lib/Target/ARM/ARMInstructionSelector.cpp
  lib/Target/X86/X86InstructionSelector.cpp
  test/TableGen/GlobalISelEmitter.td
  utils/TableGen/GlobalISelEmitter.cpp
  utils/llvm-gisel-cov.py

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