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[patch] Speed up find_pc_section


While working on something else, I noticed find_pc_section consuming 90%+
of CPU in my GDB profiles :-(

It is called from quite a number of places, and is surprisingly
inefficient. Further, it exhibits yet another quadratic slowdown on number
of objfiles, as the attached test case demonstrates.

Running "perl NNN" generates NNN shared libs, and a main executable,
which crashes with NNN+C levels in stack trace, crossing all shared libs.

I then collected timing like this:
time gdb64-cvs -ex run -ex where -ex quit ./a.out > /dev/null

Here are user-time results before the patch (clearly showing non-linear

32:  0m0.426s
64:  0m1.344s
128: 0m5.254s
256: 0m35.792s
512: 4m55.999s

Attached patch turns linear search into binary search, speeding up
find_pc_section drastically :-)

Here are the same user-time results after the patch:

128: 0m1.064s
256: 0m3.062s
512: 0m10.675s

Tested on Linux/x86_64 with no regressions.

Paul Pluzhnikov

Attachment: gdb-find_pc_section-20090716.txt
Description: Text document

Description: Perl program

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