patch to reduce register pressure from strength reduction

[Joern Rennecke]

> I came across this problem trying to bootstrap on x86-linux with the
> following
> flags "-O9 -march=pentiumpro -mcpu=pentiumpro -funroll-loops
> -fomit-frame-pointer".
> The bootstrap fails when compiling gcc/reload1.c using the stage1/cc1
> compiler 
> due to access violation caused by a giv_inc being 0 when passed to
> INTVAL() macro.

I can reproduce this by compiling reload1.c by hand with a stage1
compiler and the options you quoted.  I'm looking into it.