gcc, clang: make the assembler part of the cache key - #2843
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GCC always assembles by spawning `as`, and clang does too when its integrated assembler is turned off, so the object file depends on a program that nothing in the cache key accounted for: two invocations with different binutils could hand each other the wrong object. Compiler detection now asks the compiler which assembler it would run and identifies it the way the compiler itself is identified, by the contents of the binary plus the version it reports. It only reaches the key when a compilation really runs an external assembler, so clang keys don't move unless -fno-integrated-as is passed, and neither do MSVC's. Keys where no assembler could be identified don't move either, which keeps existing cache entries usable and is why CACHE_VERSION stays put. A hit on a preprocessor cache entry hands back the object cache key stored in it rather than computing one, so the assembler has to be part of that key as well. Full background in https://bugzilla.mozilla.org/show_bug.cgi?id=2070810.
Codecov Report❌ Patch coverage is
Additional details and impacted files@@ Coverage Diff @@
## main #2843 +/- ##
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+ Coverage 73.84% 76.14% +2.29%
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Files 72 72
Lines 38178 39807 +1629
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+ Hits 28194 30311 +2117
+ Misses 9984 9496 -488 ☔ View full report in Codecov by Harness. 🚀 New features to boost your workflow:
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GCC always assembles by spawning
as, and clang does too when its integrated assembler is turned off, so the object file depends on a program that nothing in the cache key accounted for: two invocations with different binutils could hand each other the wrong object.Compiler detection now asks the compiler which assembler it would run and identifies it the way the compiler itself is identified, by the contents of the binary plus the version it reports. It only reaches the key when a compilation really runs an external assembler, so clang keys don't move unless -fno-integrated-as is passed, and neither do MSVC's. Keys where no assembler could be identified don't move either, which keeps existing cache entries usable and is why CACHE_VERSION stays put.
A hit on a preprocessor cache entry hands back the object cache key stored in it rather than computing one, so the assembler has to be part of that key as well.
Full background in https://bugzilla.mozilla.org/show_bug.cgi?id=2070810.