EEllis Hoag[InstrProf] Add single byte coverage mode
| 文件 | 最后提交记录 | 最后更新时间 |
|---|---|---|
[InstrProfiling] Use llvm.compiler.used if applicable for Mach-O Similar to D97585. D25456 used S_ATTR_LIVE_SUPPORT to ensure the data variable will be retained or discarded as a unit with the counter variable, so llvm.compiler.used is sufficient. It allows ld to dead strip unneeded profc and profd variables. Reviewed By: vsk Differential Revision: https://reviews.llvm.org/D105445 | 4 年前 | |
[InstrProf] Add single byte coverage mode Use the llvm flag -pgo-function-entry-coverage to create single byte "counters" to track functions coverage. This mode has significantly less size overhead in both code and data because * We mark a function as "covered" with a store instead of an increment which generally requires fewer assembly instructions * We use a single byte per function rather than 8 bytes per block The trade off of course is that this mode only tells you if a function has been covered. This is useful, for example, to detect dead code. When combined with debug info correlation [0] we are able to create an instrumented Clang binary that is only 150M (the vanilla Clang binary is 143M). That is an overhead of 7M (4.9%) compared to the default instrumentation (without value profiling) which has an overhead of 31M (21.7%). [0] https://groups.google.com/g/llvm-dev/c/r03Z6JoN7d4 Reviewed By: kyulee Differential Revision: https://reviews.llvm.org/D116180 | 4 年前 | |
[InstrProfiling] Use llvm.compiler.used if applicable for Mach-O Similar to D97585. D25456 used S_ATTR_LIVE_SUPPORT to ensure the data variable will be retained or discarded as a unit with the counter variable, so llvm.compiler.used is sufficient. It allows ld to dead strip unneeded profc and profd variables. Reviewed By: vsk Differential Revision: https://reviews.llvm.org/D105445 | 4 年前 |