Fangrui Song 3307240f05 [InstrProfiling][ELF] Make __profd_ private if the function does not use value profiling ...

On ELF, the D1003372 optimization can apply to more cases. There are two
prerequisites for making `__profd_` private:

* `__profc_` keeps `__profd_` live under compiler/linker GC
* `__profd_` is not referenced by code

The first is satisfied because all counters/data are in a section group (either
`comdat any` or `comdat noduplicates`). The second requires that the function
does not use value profiling.

Regarding the second point: `__profd_` may be referenced by other text sections
due to inlining. There will be a linker error if a prevailing text section
references the non-prevailing local symbol.

With this change, a stage 2 (`-DLLVM_TARGETS_TO_BUILD=X86 -DLLVM_BUILD_INSTRUMENTED=IR`)
clang is 4.2% smaller (1-169620032/177066968).
`stat -c %s **/*.o | awk '{s+=$1}END{print s}' is 2.5% smaller.

Reviewed By: davidxl, rnk

Differential Revision: https://reviews.llvm.org/D103717

2021-06-18 17:01:17 -07:00

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