[DLCov] Origin-Tracking: Add config options (llvm#143590)

This patch is part of a series that adds origin-tracking to the debugify
source location coverage checks, allowing us to report symbolized stack
traces of the point where missing source locations appear.

This patch adds the configuration options needed to enable this feature,
in the form of a new CMake option that enables a flag in
`llvm-config.h`; this is not an entirely new CMake flag, but a new
option, `COVERAGE_AND_ORIGIN`, for the existing flag
`LLVM_ENABLE_DEBUGLOC_COVERAGE_TRACKING`. This patch contains
documentation, but no actual implementation for the flag itself.

Author: SLTozer

llvm/CMakeLists.txt

@@ -569,8 +569,8 @@ endif()
 option(LLVM_ENABLE_CRASH_DUMPS "Turn on memory dumps on crashes. Currently only implemented on Windows." OFF)
 
 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)
+  "Enhance Debugify's line number coverage tracking; enabling this is ABI-breaking. Can be DISABLED, COVERAGE, or COVERAGE_AND_ORIGIN.")
+set_property(CACHE LLVM_ENABLE_DEBUGLOC_COVERAGE_TRACKING PROPERTY STRINGS DISABLED COVERAGE COVERAGE_AND_ORIGIN)
 
 option(LLVM_EXPERIMENTAL_KEY_INSTRUCTIONS
   "Add additional fields to DILocations to support Key Instructions" OFF)

llvm/cmake/modules/HandleLLVMOptions.cmake

@@ -200,6 +200,9 @@ string(TOUPPER "${LLVM_ENABLE_DEBUGLOC_COVERAGE_TRACKING}" uppercase_LLVM_ENABLE
 
 if( uppercase_LLVM_ENABLE_DEBUGLOC_COVERAGE_TRACKING STREQUAL "COVERAGE" )
   set( LLVM_ENABLE_DEBUGLOC_COVERAGE_TRACKING 1 )
+elseif( uppercase_LLVM_ENABLE_DEBUGLOC_COVERAGE_TRACKING STREQUAL "COVERAGE_AND_ORIGIN" )
+  set( LLVM_ENABLE_DEBUGLOC_COVERAGE_TRACKING 1 )
+  set( LLVM_ENABLE_DEBUGLOC_ORIGIN_TRACKING 1 )
 elseif( uppercase_LLVM_ENABLE_DEBUGLOC_COVERAGE_TRACKING STREQUAL "DISABLED" OR NOT DEFINED LLVM_ENABLE_DEBUGLOC_COVERAGE_TRACKING )
   # The DISABLED setting is default and requires no additional defines.
 else()

llvm/docs/CMake.rst

@@ -482,11 +482,14 @@ enabled sub-projects. Nearly all of these variable names begin with
 **LLVM_ENABLE_DEBUGLOC_COVERAGE_TRACKING**:STRING
   Enhances Debugify's ability to detect line number errors by storing extra
   information inside Instructions, removing false positives from Debugify's
-  results at the cost of performance. Allowed values are `DISABLED` (default)
-  and `COVERAGE`. `COVERAGE` tracks whether and why a line number was
-  intentionally dropped or not generated for an instruction, allowing Debugify
-  to avoid reporting these as errors; this comes with a small performance cost
-  of ~0.1%. `COVERAGE` is an ABI-breaking option.
+  results at the cost of performance. Allowed values are `DISABLED` (default),
+  `COVERAGE`, and `COVERAGE_AND_ORIGIN`. `COVERAGE` tracks whether and why a
+  line number was intentionally dropped or not generated for an instruction,
+  allowing Debugify to avoid reporting these as errors; this comes with a small
+  performance cost of ~0.1%. `COVERAGE_AND_ORIGIN` additionally stores a
+  stacktrace of the point where each DebugLoc is unintentionally dropped,
+  allowing for much easier bug triaging at the cost of a ~10x performance
+  slowdown. `COVERAGE` and `COVERAGE_AND_ORIGIN` are ABI-breaking options.
 
 **LLVM_ENABLE_DIA_SDK**:BOOL
   Enable building with MSVC DIA SDK for PDB debugging support. Available

llvm/include/llvm/Config/llvm-config.h.cmake

@@ -133,4 +133,8 @@
    and to 0 otherwise. */
 #cmakedefine01 LLVM_ENABLE_DEBUGLOC_COVERAGE_TRACKING
 
+/* Define to 1 to enable expensive tracking of the origin of debug location
+   coverage bugs, and to 0 otherwise. */
+#cmakedefine01 LLVM_ENABLE_DEBUGLOC_ORIGIN_TRACKING
+
 #endif