Christophe Lyon <[email protected]> writes:
> On Thu, 13 Aug 2020 at 03:54, qiaopeixin <[email protected]> wrote:
>>
>> Thanks for the review and commit.
>>
>> All the best,
>> Peixin
>>
>> -----Original Message-----
>> From: Richard Sandiford [mailto:[email protected]]
>> Sent: 2020年8月13日 0:25
>> To: qiaopeixin <[email protected]>
>> Cc: [email protected]
>> Subject: Re: [PATCH] AArch64: Add if condition in aarch64_function_value
>> [PR96479]
>>
>> qiaopeixin <[email protected]> writes:
>> > Hi,
>> >
>> > The test case vector-subscript-2.c in the gcc testsuit will report an ICE
>> > in the expand pass since '-mgeneral-regs-only' is incompatible with the
>> > use of V4SI mode. I propose to report the diagnostic information instead
>> > of ICE, and the problem has been discussed on PR 96479.
>> >
>> > I attached the patch to solve the problem. Bootstrapped and tested on
>> > aarch64-linux-gnu. Any suggestions?
>>
>> Thanks, pushed. I was initially sceptical because raising an error here and
>> in aarch64_layout_arg is a hack. Both functions are just query functions
>> and shouldn't have any side effects.
>>
>> The approach we took for FP modes seemed better: we define the FP move
>> patterns unconditionally, and raise an error if we try to emit an FP move
>> with !TARGET_FLOAT. This defers any error reporting until we actually try
>> to generate code that depends on TARGET_FLOAT.
>>
>> But I guess SIMD stuff is different. There's no reason in principle why you
>> can't use:
>>
>> unsigned short __attribute__((vector_size(8)))
>>
>> *within* a function with -mgeneral-regs-only. It would just need to be
>> emulated, in the same way as for:
>>
>> unsigned short __attribute__((vector_size(4)))
>>
>> So it would be wrong to define the SIMD move patterns unconditionally and
>> raise an error there.
>>
>> So all in all, I agree this is the best we can do given the current
>> infrastructure.
>>
>
> Since this patch was committed my buildbot is broken for
> aarch64-linux-gnu because it now fails to build glibc-2.29:
> ../stdlib/bits/stdlib-float.h: In function 'atof':
> ../stdlib/bits/stdlib-float.h:26:1: error: '-mgeneral-regs-only' is
> incompatible with the use of floating-point types
Thanks for the heads-up. I've reverted the patch for now.
Looking more closely, it seems like aarch64_init_cumulative_args
already tries to catch the problem that the patch was fixing:
if (!silent_p
&& !TARGET_FLOAT
&& fndecl && TREE_PUBLIC (fndecl)
&& fntype && fntype != error_mark_node)
{
const_tree type = TREE_TYPE (fntype);
machine_mode mode ATTRIBUTE_UNUSED; /* To pass pointer as argument. */
int nregs ATTRIBUTE_UNUSED; /* Likewise. */
if (aarch64_vfp_is_call_or_return_candidate (TYPE_MODE (type), type,
&mode, &nregs, NULL, false))
aarch64_err_no_fpadvsimd (TYPE_MODE (type));
}
The only reason it doesn't work for the testcase is that TREE_PUBLIC
condition. TBH I'm not sure why it or the fndecl test is there:
this is just as problematic when calling via a function pointer
or when calling a static function.
Richard
