Commit Graph

4 Commits

Author SHA1 Message Date
Fangrui Song 9ff36df5a4 [PGO][InstrProf][test] Convert to opaque pointers and fix some stale tests 2022-07-16 11:42:35 -07:00
Fangrui Song acead46a10 [test] Migrate legacy InstrProfiling tests to new PM 2022-07-16 01:10:08 -07:00
Daniel Kiss b0343a38a5 Support the min of module flags when linking, use for AArch64 BTI/PAC-RET
LTO objects might compiled with different `mbranch-protection` flags which will cause an error in the linker.
Such a setup is allowed in the normal build with this change that is possible.

Reviewed By: pcc

Differential Revision: https://reviews.llvm.org/D123493
2022-04-13 09:31:51 +02:00
Ellis Hoag 11d3074267 [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
2022-01-27 17:38:55 -08:00