Re: Patch for scan_loop [Re: EGCS EXTREME optimization times...]

[Franz Sirl <Franz dot Sirl-kernel at lauterbach dot com>]

Am Sat, 13 Feb 1999 schrieb Jeffrey A Law:
>In message <14020.52936.784843.61964@ongaonga.elec.canterbury.ac.nz>you write
>  > Michael Hayes writes:
>  >  > The culprit is the loop optimizer (but not strength reduction this
>  >  > time).  During scan_loop, loop_reg_used_before_p is called for most of
>  >  > the loop insns and since loop_reg_used_before_p checks every loop insn
>  >  > we have quadratic behavior.  
>  > 
>  > Here's a patch that just swaps the calls to loop_reg_used_before_p
>  > and reg_in_basic_block_p.  There's no point embarking on a long search
>  > if the subsequent test will fail.  With -O2 the compilation time drops
>  > from 333 seconds to 2 seconds with David's testcase.
>  > 
>  > Michael.
>  > 
>  > 	* loop.c (scan_loop): Call reg_in_basic_block_p before
>  > 	loop_reg_used_before_p.
>This is fine.  I'm going to install it on the egcs-1.1 branch, can you please
>install it into the mainline sources?

Hmm, on the egcs_1_1_branch this patch solves this testcase on ppc-linux-gnu:

FAIL: gcc.c-torture/compile/980329-1.c,  -O2 -fomit-frame-pointer
-finline-functions -funroll-all-loops

I'm a little bit worried about that, cause this thread implied that this patch
should only improve compilation speed and not change the behaviour of the
compiler.

Thoughts?
Franz.