The following patch adds new knob to make GCC perform several iterations of early optimizations and inlining.
This is for dont-care-about-compile-time-optimize-all-you-can scenarios.
Performing several iterations of optimizations does significantly improve code
speed on a certain proprietary source base. Some hand-tuning of the parameter
value is required to get optimum performance. Another good use for this option
is for search and ad-hoc analysis of cases where GCC misses optimization
opportunities.
With the default setting of '1', nothing is changed from the current status quo.
The patch was bootstrapped and regtested with 3 iterations set by default on
i686-linux-gnu. The only failures in regression testsuite were due to latent
bugs in handling of EH information, which are being discussed in a different
thread.
Performance impact on the standard benchmarks is not conclusive, there are
improvements in SPEC2000 of up to 4% and regressions down to -2%, see [*].
SPEC2006 benchmarks will take another day or two to complete and I will update
the spreadsheet then. The benchmarks were run on a Core2 system for all
combinations of {-m32/-m64}{-O2/-O3}.
Effect on compilation time is fairly predictable, about 10% compile time
increase with 3 iterations.
OK for trunk?
[*]
https://docs.google.com/spreadsheet/ccc?key=0AvK0Y-Pgj7bNdFBQMEJ6d3laeFdvdk9lQ1p0LUFkVFE&hl=en_US
Thank you,
--
Maxim Kuvyrkov
CodeSourcery / Mentor Graphics
fsf-gcc-iter-eipa.ChangeLog
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fsf-gcc-iter-eipa.patch
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