Re: [PATCH][ARM] PR target/67929 Tighten vfp3_const_double_for_bits checks

[Kyrill Tkachov <kyrylo dot tkachov at arm dot com>]

Ping.

https://gcc.gnu.org/ml/gcc-patches/2015-10/msg01350.html
and the backport for 4.9/5
https://gcc.gnu.org/ml/gcc-patches/2015-10/msg01351.html

Thanks,
Kyrill


On 14/10/15 13:23, Kyrill Tkachov wrote:
> Hi all,
>
> This patch fixes the referenced PR by rewriting the vfp3_const_double_for_bits function in arm.c
> The function is supposed to accept positive CONST_DOUBLE rtxes whose value is an exact power of 2
> and whose log2 is between 1 and 32. That is values like 2.0, 4.0, 8.9, 16.0 etc...
>
> The current implementation seems to have been written under the assumption that exact_real_truncate returns
> false if the input value is not an exact integer, whereas in fact exact_real_truncate returns false if the
> truncation operation was not exact, which are different things. This would lead the function to accept any
> CONST_DOUBLE that can truncate to a power of 2, such as 4.9, 16.2 etc.
>
> In any case, I've rewritten this function and used the real_isinteger predicate to check if the real value
> is an exact integer.
>
> The testcase demonstrates the kind of wrong code that this patch addresses.
>
> This bug appears on GCC 5 and 4.9 as well, but due to the recent introduction of CONST_DOUBLE_REAL_VALUE
> this patch doesn't apply on those branches. I will soon post the backportable variant.
>
> Bootstrapped and tested on arm-none-linux-gnueabihf.
>
> Ok for trunk?
>
> Thanks,
> Kyrill
>
> 2015-10-12  Kyrylo Tkachov  <kyrylo.tkachov@arm.com>
>
>     PR target/67929
>     * config/arm/arm.c (vfp3_const_double_for_bits): Rewrite.
>     * config/arm/constraints.md (Dp): Update callsite.
>     * config/arm/predicates.md (const_double_vcvt_power_of_two): Likewise.
>
> 2015-10-12  Kyrylo Tkachov  <kyrylo.tkachov@arm.com>
>
>     PR target/67929
>     * gcc.target/arm/pr67929_1.c: New test.