[llvm-commits] Avoid O(#registers*#basicblocks) memory use in LiveVariables

[Jeffrey Yasskin]

I just wanted to double-check that you're not worried about the extra
memory use for small functions, and the potential for quadratic time
with a higher constant, before I commit this.

On Fri, May 22, 2009 at 4:03 PM, Evan Cheng <evan.cheng at apple.com> wrote:
> Excellent. Thanks!
>
> Evan
>
> On May 22, 2009, at 3:41 PM, Jeffrey Yasskin wrote:
>
>> LiveVariables::VarInfo contains two BitVectors, AliveBlocks and
>> UsedBlocks, which have as many entries as there are basic blocks in
>> the function. I believe LiveVariables::getVarInfo creates a VarInfo
>> struct for every register in the function, leading to quadratic space
>> use. On a particular function with approximately 30k basic blocks and
>> 280k instructions, which I've uploaded to
>> http://jeffrey.yasskin.info/dump/big_module.bc.bz2, this took
>> approximately 1.6GB of memory to codegen. The attached patch changes
>> these two variables to SparseBitVectors, which makes the memory use go
>> down to ~420MB (on Mac; llc on linux goes from 1.6GB->~900MB).
>>
>> It's possible that this patch merely trades quadratic space on rare
>> large functions for larger space and quadratic time on more common
>> small functions, but I don't know enough about how LiveVariables works
>> to know.
>>
>> This passes LLVM's `make check`, except for the Frontend tests that
>> never pass for me.
>>
>> Jeffrey
>> <
>> smaller_livevars.patch>_______________________________________________
>> llvm-commits mailing list
>> llvm-commits at cs.uiuc.edu
>> http://lists.cs.uiuc.edu/mailman/listinfo/llvm-commits
>
> _______________________________________________
> llvm-commits mailing list
> llvm-commits at cs.uiuc.edu
> http://lists.cs.uiuc.edu/mailman/listinfo/llvm-commits
>