Instrumentation-based FDO

In the instrumentation-based FDO scenario, two compilations are required. The first compilation is performed with compilation option -fprofile-generate[=path]. After a series of typical scenario tests, the profile data is generated. The second compilation is performed with compilation option -fprofile-use[=path], during which AutoBOLT converts the instrumentation data to a BOLT profile and automatically enables post-link optimization.

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# Perform instrumentation to generate gcno.
gcc -O3 -fprofile-generate[=path] -fprofile-update=atomic -o test test.c
# Perform a test to obtain gcda.
./test
# Use the generated gcda to build a new executable file.
gcc -O3 -Wl,-q -fprofile-use[=path] -fprofile-correction -Wno-error=coverage-mismatch -Wno-error=missing-profile -fauto-bolt -fbolt-target=test -o test test.c