How to replace -O1 with corresponding -f's?

[Sergei Organov <osv at topconrd dot ru>]

Hi,

Using gcc compiled from gcc-4_0-branch, in an attempt to see which
particular optimization option makes my test case to be mis-optimized, I
try to replace -O1 (which toggles on the problem) with corresponding set
of -fxxx optimization options. I first compile my code like this:

gcc -v -save-temps -fverbose-asm -O1 -o const.o -c const.c

then merge the cc1 command that gcc invokes to compile the preprocessed
source (as gcc doesn't seem to pass some of -f forward to cc1) with the
entire list of options taken from resulting const.s file (found at the
line " # options enabled: ..." and further), and compile using this.

In the resulting const.s file there are 2 problems:

1. "options enabled" output almost matches those from the initial (-O1)
   invocation, but -floop-optimize is missing though it does exist in
   the "options passed" output.

2. The resulting assembly is different from what I get with -O1 and
   doesn't contain the mis-optimization I'm trying to debug though it
   doesn't seem to have anything to do with loops. For reference, the
   code I'm trying to compile is:

        extern double const osv;
        double const osv = 314314314;
        double osvf() { return osv; }

Am I doing something stupid or what? How one finds out what optimization
pass misbehaves?

-- 
Sergei.