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Re: [PATCH 6/9] Add --param tunables for the initial size of the type merging hash tables

On Mon, Apr 22, 2013 at 01:49:39PM +0200, Richard Biener wrote:
> On Fri, Apr 19, 2013 at 11:31 PM, Andi Kleen <> wrote:
> > From: Andi Kleen <>
> >
> > WPA can spend a lot of time just resizing the type merging hash tables.
> > This adds experimental --params to size them large initially. On my large
> > LTO build I get a 1.1% improvement in build time from presizing the hash
> > tables to a large enough value.
> With what values?  Certainly we will have at least as many hashes

For the test I used just the final values from -flto-report from a previous
run.  I know it's cheating. But it's reasonable to just always use a 
large table, unless someone comes up with a nice way to pre estimate.

> as types, so increasing the hash cache sizes to the size of the types
> (thus use the same --param) would be obvious.  Likewise there will

iirc the caches were usually smaller than the types from lto-report. Perhaps
they have less collisions.


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