fcombine-regs

piranha · Post by **piranha** » Sat Jan 06, 2007 4:56 pm

What is fcombine-regs? I found this in the linux kernel 0.01 makefile.

thx

Alboin · Post by **Alboin** » Sat Jan 06, 2007 5:09 pm

Ahem,

Allow the combine pass to combine an  instruction  that
copies  one register into another.  This might or might
not produce better code when used in addition to -O.  I
am  interested  in  hearing  about  the difference this
makes.

This is from an archive of GCC 1.36's manual. It's no longer used. At least that's what my GCC tells me in the form of:

Code: Select all

cc1: error: unrecognized option `-fcombine-regs'

piranha · Post by **piranha** » Sat Jan 06, 2007 5:10 pm

For example:

gcc -fcombine-regs t.c -o t.o

i get it to say: unrecognized command line option "-fcombine-regs"

I don't know if this is the reason, but when I compile linux it has hundreds of errors.

Alboin · Post by **Alboin** » Sat Jan 06, 2007 5:13 pm

No, I don't think the lack of -fcombine-regs should produce any errors, as it is just an optimization. (Yet, I could be wrong...

) However, the hundreds of errors might be coming from various changes that have occurred over 15 years in different tools....Maybe?

Brynet-Inc · Post by **Brynet-Inc** » Sat Jan 06, 2007 8:09 pm

The original linux kernel was compiled under minix.

I remember seeing someone's site that made a patch or alternative release that is buildable on modern systems.

Can't remember where..