[PATCH][ARM] optimizing _muldi3 for Thumb

[Paul Brook]

On Saturday 02 August 2008, Doug Kwan (關振德) wrote:
>    Here is an updated patch.

This is bad in several ways.

The condition for pure Thumb-1 code is completely wrong, you want 
__ARM_ARCH_6M__, exactly the same as all the other Thumb-1 only code.
For most purposes ARMv6-M is Thumb-1. ARM marketing sometimes call 
it "Thumb-2" to deliberately confuse people. Please don't do this.

> +/* We cannot use the faster ARM version for THUMB libgcc on V6 and V6M
> since  Cortex-M1 does not run ARM code. */

Shows you've completely misunderstood which architecture variants have which 
features.

umull is only available on v3M and later cores.

The Thumb-2 code is just dumb (Yes I know it's what the compiler generates, 
but gcc is notoriously bad at doubleword arithmetic).  mla is not Thumb-2 
specific, and using it certainly doesn't require additional register pushes.  
AFAICS there's no reason to have different code for ARM and Thumb-2.

Paul