llvm-project

cadc31b1 - [CodeGen] Source-qualify hashes of module-local globals for GFM and outliner (#219938)

[CodeGen] Source-qualify hashes of module-local globals for GFM and outliner (#219938) Global function merging and outliner compare hashes across modules. Some globals are hashed by name, so two modules that each define a same-named global with local linkage produce identical operand hashes although they denote different storage. The hash collision caused both GFM and GFO to make quite a few non-beneficial optimization decisions. Add a `SourceQualifyLocalGlobals` option to IR `StructuralHash` and MIR `stableHashValue`. When set, the name-based hash of a global with local linkage is combined with the source file name of its module. The module identifier itself is not suitable: the linker may name the module after an unstable temporary LTO object file, which would make the supposedly stable hash vary from run to run and between the generate and use rounds. Content-based hashes are unchanged, so equivalent literals still merge across modules. The option defaults to off, so other users of `stableHashValue` and `StructuralHash` keep their hashes.