[PATCH][ARM] optimizing _muldi3 for Thumb

Mark Mitchell mark@codesourcery.com
Mon Jul 28 09:57:00 GMT 2008

Doug Kwan (Ãö®¶¼w) wrote:
> Ok.  I will update my patch to include a thumb-2 implementation then.
> I will resubmit my patch after testing it with thumb-2 only.  There is
> no thumb (not thumb-2) only CPU I guess?

As I said, Cortex-M1 is close to the original Thumb.  It's technically
Thumb-2, but it's missing a lot of the Thumb-2 instructions.  You should
look at ARM's ISA manuals to make sure it has what you need.

Of course, even for CPUs with both modes, there's often a cost to
switching from Thumb to ARM and back, so it's certainly better if a
Thumb libgcc multilib doesn't end up using ARM code.

And I think Nathan Froyd's question is a good one; if there's an
efficient instruction sequence for this, let's not use libgcc at all,
unless we're optimizing for size.  When optimizing for speed, we should
avoid the call entirely.

Mark Mitchell
(650) 331-3385 x713

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