[PATCH][ARM] Fix ldrd offsets

[Wilco Dijkstra]

Ramana Radhakrishnan wrote:
> On Thu, Nov 3, 2016 at 12:20 PM, Wilco Dijkstra <Wilco.Dijkstra@arm.com> wrote:

>           HOST_WIDE_INT val = INTVAL (index);
> -         /* ??? Can we assume ldrd for thumb2?  */
> -         /* Thumb-2 ldrd only has reg+const addressing modes.  */
> -         /* ldrd supports offsets of +-1020.
> -            However the ldr fallback does not.  */
> -         return val > -256 && val < 256 && (val & 3) == 0;
> +         /* Thumb-2 ldrd only has reg+const addressing modes.
> +            Assume we emit ldrd or 2x ldr if !TARGET_LDRD.
> +            If vldr is selected it uses arm_coproc_mem_operand.  */
> +         if (TARGET_LDRD)

> I suspect this should be : if (TARGET_LDRD && !fix_cm3_ldrd)  - I am a
> bit worried about this change because of the non-uniformity with ldr
> and the fallout with other places where things may break with this.  I
> would like a test with -mcpu=cortex-m3/-mthumb as well for an
> arm-none-eabi target to see what the fallout of this change is on that

Well it works fine given that Thumb-2 supports add/sub up to 4KB, so
the existing expansion into add+ldrd for the fix_cm3_ldrd case works fine.
I ran a bootstrap with fix_cm3_ldrd forced to true, and that completed without
any issues.

Wilco