[llvm-commits] [gcc-plugin] r83276 - /gcc-plugin/trunk/llvm-backend.cpp

Duncan Sands baldrick at free.fr
Sun Oct 4 07:24:05 PDT 2009

Hi Edwin,

>> Don't bother running the garbage collector.  The original idea was that once
>> functions are converted to LLVM IR, they can be discarded.  This was done by
>> estimating the amount of memory that could be recovered, and running the garbage
>> collector if that seemed beneficial.  However even on huge testcases this never
>> saved more than a megabyte or three, while it increased compile time considerably.
> This seems to suggest that turning off the garbage collector makes it
> faster.

yes, turning it off makes it much faster at -O0.

>> In fact, if the garbage collector isn't run at all then gcc-4.5 with the plugin
>> uses up less memory than gcc-4.5 (presumably because RTL is fat), and about the
>> same or less than llvm-gcc (on insn-attrtab.c a bit more than 5% less).  Turning
>> off the garbage collector almost doubles -O0 compile times, making them about the
>> same as llvm-gcc.
> However this suggests that turning it off slows it down.
> Did you mean "compile time" or "speed"?
> If it doubles compile time, why turn it off?
> Best regards,
> --Edwin

I meant halves, not doubles :)



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