[NFC][KeyInstr] Add (LLVM_)EXPERIMENTAL_KEY_INSTRUCTIONS (cmake/)definition

[OCHyams]

Key Instructions will start development behind a compile time flag to avoid
passing on the increased memory usage to all debug builds. We're working on
improving DILocation memory characteristics simultaneously; once that work lands
we can remove EXPERIMENTAL_KEY_INSTRUCTIONS.

This patch doesn't add any code, it's just so we can get the SIE buildbot
building with the new option right away.

[llvmbot]

@llvm/pr-subscribers-debuginfo

Author: Orlando Cazalet-Hyams (OCHyams)

Changes

Key Instructions will start development behind a compile time flag to avoid
passing on the increased memory usage to all debug builds. We're working on
improving DILocation memory characteristics simultaneously; once that work lands
we can remove EXPERIMENTAL_KEY_INSTRUCTIONS.

This patch doesn't add any code, it's just so we can get the SIE buildbot
building with the new option right away.

---

Full diff: https://github.com/llvm/llvm-project/pull/131344.diff

2 Files Affected:

• (modified) llvm/CMakeLists.txt (+3)
• (modified) llvm/cmake/modules/HandleLLVMOptions.cmake (+4)

diff --git a/llvm/CMakeLists.txt b/llvm/CMakeLists.txt
index c5d3e23a47f0e..18b6ee85fae8d 100644
--- a/llvm/CMakeLists.txt
+++ b/llvm/CMakeLists.txt
@@ -545,6 +545,9 @@ set(LLVM_ENABLE_DEBUGLOC_COVERAGE_TRACKING "DISABLED" CACHE STRING
   "Enhance Debugify's line number coverage tracking; enabling this is ABI-breaking. Can be DISABLED, or COVERAGE.")
 set_property(CACHE LLVM_ENABLE_DEBUGLOC_COVERAGE_TRACKING PROPERTY STRINGS DISABLED COVERAGE)
 
+option(LLVM_EXPERIMENTAL_KEY_INSTRUCTIONS
+  "Add additional fields to DILocations to support Key Instructions" OFF)
+
 set(WINDOWS_PREFER_FORWARD_SLASH_DEFAULT OFF)
 if (MINGW)
   # Cygwin doesn't identify itself as Windows, and thus gets path::Style::posix
diff --git a/llvm/cmake/modules/HandleLLVMOptions.cmake b/llvm/cmake/modules/HandleLLVMOptions.cmake
index 5db06ccdadbeb..c2c04051ef3ce 100644
--- a/llvm/cmake/modules/HandleLLVMOptions.cmake
+++ b/llvm/cmake/modules/HandleLLVMOptions.cmake
@@ -206,6 +206,10 @@ else()
   message(FATAL_ERROR "Unknown value for LLVM_ENABLE_DEBUGLOC_COVERAGE_TRACKING: \"${LLVM_ENABLE_DEBUGLOC_COVERAGE_TRACKING}\"!")
 endif()
 
+if(LLVM_EXPERIMENTAL_KEY_INSTRUCTIONS)
+  add_compile_definitions(EXPERIMENTAL_KEY_INSTRUCTIONS)
+endif()
+
 if( LLVM_REVERSE_ITERATION )
   set( LLVM_ENABLE_REVERSE_ITERATION 1 )
 endif()

[jmorse]

LGTM; this is how the RemoveDIs prototype was implemented, hopefully like RemoveDIs it'll avoid un-necessary interference with other folks while still getting test coverage.

[OCHyams]

I hope it's not too pushy in landing this, as it's not clear the RFC for key instructions is "accepted". This can easily be reverted; I'm just trying to set up the testing path.