[PATCH] analysis of global statics and removal associated vdefs and vuses
Fri Aug 27 18:08:00 GMT 2004
On Fri, 2004-08-27 at 12:34, Daniel Jacobowitz wrote:
> On Fri, Aug 27, 2004 at 12:27:54PM -0400, Diego Novillo wrote:
> > On Thu, 2004-08-26 at 18:01, Kenneth Zadeck wrote:
> > > 3) use of the analysis in (2) so that the code in
> > > gcc/tree-ssa-operands.c reduces the number of vdefs and vuses that are
> > > inserted to account for call clobbering.
> > >
> > I've started reading the patch. So far I've noticed a slowdown in
> > compile time that I wasn't expecting. On cc1-i-files there's a 2% slow
> > down and on PR8361 there's about 13% (on x86-64). I've still not
> > characterized it. More to follow later.
> > There is a slight reduction in the number of virtual operands on
> > cc1-i-files (2,816 fewer virtual operands or about 0.1%).
> > As we talked earlier, one of the things that could benefit this analysis
> > is the marking of standard library calls that do not clobber any global
> > statics. For instance, printf does not call back into the user program,
> > so a call to printf can't really clobber any of the variables we are
> > interested in.
> Printf is a bad example. There are several exceptions to your
> - User-defined printf callbacks. I doubt any standard covers this,
> but at least glibc supports it. Other libraries may also.
> - The %n specifier clobbers the value pointed to by one of printf's
Huh. Nice to know. Perhaps glibc might help with some attribute
promising no nasty side effects. In any case, something for the FE
folks to think about.
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