Re: [PATCH][ARM] Restrict {load,store}_multiple expanders to MAX_LD_STM_OPS regs

[Ramana Radhakrishnan <ramana dot gcc at googlemail dot com>]

On Tue, Apr 14, 2015 at 1:37 PM, Kyrill Tkachov <kyrylo.tkachov@arm.com> wrote:
> Hi all,
>
> The load/store-multiple expanders reject a number of registers outside of
> [2-14]
> but the arm_gen_{load,store}_multiple functions that they called down to
> have an even
> stricter restriction of <= MAX_LDM_STM_OPS that is <= 4. If load_multiple
> was called with
> a number of regs larger than 4 the assert would trigger and we'd ICE.
> This patch fixes that possibility by FAILing in expansion if the number of
> requested
> regs is > MAX_LDM_STM_OPS.
>
> The reason we never hit this currently is that the load,store_multiple
> standard names are
> only used in a single place in expr.c to load the argument registers from to
> a function call.
> By a happy coincidence for arm the number of argument registers is 4 so we
> never exceed that.
> The arm backend never calls the load,store_multiple expanders directly but
> rather the
> arm_gen* functions and it makes sure that they're never called with anything
>  > MAX_LDM_STM_OPS.
>
> I hit this issue only due to a buggy change I made to expr.c that ended up
> requesting a
> load_multiple of 5 registers which the expander should have rejected but it
> didn't,
> causing an ICE.
>
> If we add more uses of load/store_multiple in the midend this issue will be
> a loaded gun.
>
> Bootstrapped and tested on arm-none-linux-gnueabihf.
>
> Ok for trunk?

Whoops ! Good catch.

Ok.

Ramana

>
> Thanks,
> Kyrill
>
> 2015-04-14  Kyrylo Tkachov  <kyrylo.tkachov@arm.com>
>
>     * config/arm/arm.md (load_multiple): Reject operand 2 greater than
>     MAX_LDM_STM_OPS.
>     (store_multiple): Likewise.