Re: C++ PATCH to integrate c++-delayed-folding branch

[David Edelsohn <dje.gcc@gmail.com>]

On Mon, Nov 16, 2015 at 10:47 PM, Jason Merrill <jason@redhat.com> wrote:
> On 11/16/2015 09:39 PM, David Edelsohn wrote:
>>
>> The PPC port seems to be bootstrapping again, but I'm not sure why.
>> Mike Meissner's patch only should have affected long double.
>
>
>> It's hard to know if there is a latent bug that has gone back into hiding.
>
>
> The problem was twofold:
>
> 1) VSX_L included IFmode, but VSa didn't, so expanding various patterns over
> VSX_L generated an IFmode insn that still had <VSa> scattered around.
> Mike's patch fixed this.
>
> 2) The delayed folding merge changed
>
>   __builtin_constant_p (non-constant-expr && false)
>
> to be false because the operand is not a C++ constant expression. Previously
> we had seen that the IFmode insn was inactive because its test was known to
> be false, but with this change we needed to evaluate its test at runtime, so
> we had to parse the insn itself, so we ran into problem #1.
>
> I have a patch to fix the __builtin_constant_p regression which I will be
> checking in shortly.

Thanks for debugging and fixing this!

- David