[cmake] Fix relative paths in prefix map #74132
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Previously, building a debug version of LLVM when -ffile-prefix-map would cause llvm project paths to be prefixed by the build directory, so source locations would be "../build/llvm/...". This happened because the relative path went in the wrong direction, from source-dir to build-dir instead of from build-dir to source-dir. This patch swaps the directionality of the relative paths so that they get a proper prefix from the build directory. Given a build dir at /build and a project directory at /llvm-project, we get source locations like: "../llvm-project/llvm/lib/Transforms/...", which a debugger can resolve once pointed to the correct directory.
petrhosek approved these changes Dec 1, 2023
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When building debug version of LLVM with
LLVM_USE_RELATIVE_PATHS_IN_FILES=Onwould cause source paths to be incorrect, and be prefixed by the build directory. This lead to source locations like the following:../build/llvm/.... Such paths do not exist, and existing debuggers can't adjust their search location because of the incorrect prefix. Ultimately, this happened because the relative path creation goes in the wrong direction, from source-dir to build-dir instead of from build-dir to source-dir.This patch swaps the directionality of the relative paths so that they get a proper prefix from the build directory. Given a build dir at
/buildand a project directory at/llvm-project, we get source locations like:../llvm-project/llvm/lib/Transforms/..., which a debugger can resolve once pointed to the correct project directory.