Re: [PATCH] convert braced initializers to strings (PR 71625)

[Richard Biener <richard.guenther@gmail.com>]

On August 15, 2018 12:28:55 PM GMT+02:00, James Greenhalgh <James.Greenhalgh@arm.com> wrote:
>On Tue, Aug 14, 2018 at 09:34:08PM -0500, Martin Sebor wrote:
>> On 08/14/2018 09:24 AM, Martin Sebor wrote:
>> > On 08/14/2018 09:08 AM, Martin Sebor wrote:
>> >> On 08/14/2018 07:27 AM, James Greenhalgh wrote:
>> >>> On Wed, Aug 08, 2018 at 07:17:07PM -0500, Martin Sebor wrote:
>> >>>> On 08/08/2018 05:08 AM, Jason Merrill wrote:
>> >>>>> On Wed, Aug 8, 2018 at 9:04 AM, Martin Sebor <msebor@gmail.com>
>wrote:
>> >>>>>> On 08/07/2018 02:57 AM, Jason Merrill wrote:
>> >>>>>>>
>> >>>>>>> On Wed, Aug 1, 2018 at 12:49 AM, Martin Sebor
><msebor@gmail.com>
>> >>>>>>> wrote:
>> >>>>>>>>
>> >>>>>>>> On 07/31/2018 07:38 AM, Jason Merrill wrote:
>> >>>
>> >>> <snip>
>> >>>
>> >>>> Done in the attached patch.  I've also avoided dealing with
>> >>>> zero-length arrays and added tests to make sure their size
>> >>>> stays is regardless of the form of their initializer and
>> >>>> the appropriate warnings are issued.
>> >>>>
>> >>>> Using build_string() rather than build_string_literal() needed
>> >>>> a tweak in digest_init_r().  It didn't break anything but since
>> >>>> the array type may not have a domain yet, neither will the
>> >>>> string.  It looks like that may get adjusted later on but I've
>> >>>> temporarily guarded the code with #if 1.  If the change is
>> >>>> fine I'll remove the #if before committing.
>> >>>>
>> >>>> This initial patch only handles narrow character initializers
>> >>>> (i.e., those with TYPE_STRING_FLAG set).  Once this gets some
>> >>>> exposure I'd like to extend it to other character types,
>> >>>> including wchar_t.
>> >>>
>> >>> Hi Martin,
>> >>>
>> >>> This causes issues for the AArch64 tests (full list below).
>> >>>
>> >>> I see an error message on the following construct:
>> >>>
>> >>>   void foo (void)
>> >>>   {
>> >>>     __Poly8_t x[4] = { 1, 2, 3, 4 };
>> >>>   }
>> >>>
>> >>>   init.c:3:20: error: array of inappropriate type initialized
>from
>> >>> string constant
>> >>>   3 |   __Poly8_t x[4] = { 1, 2, 3, 4 };
>> >>>     |
>> >>>
>> >>> __Poly8_t is a type we define in our backend, through a
>convoluted
>> >>> set of
>> >>> functions, which operates a lot like an unsigned, QI mode type.
>> >>
>> >> I see the error with my aarch64 cross-compiler .  The new code
>> >> that does the conversion of array initializers to STRING_CSTs
>> >> looks for the TYPE_STRING_FLAG() to be set on the type of
>> >> the array elements.  Perhaps __Poly8_t should not have the flag
>> >> set?  (If it needs it then I think we'd have to only consider
>> >> named character types.)
>> >
>> > The change below gets rid of the compilation error.  I don't
>> > know if it's appropriate for the aarch64 back end:
>> >
>> > Index: gcc/config/aarch64/aarch64-builtins.c
>> > ===================================================================
>> > --- gcc/config/aarch64/aarch64-builtins.c    (revision 263537)
>> > +++ gcc/config/aarch64/aarch64-builtins.c    (working copy)
>> > @@ -643,6 +643,7 @@ aarch64_init_simd_builtin_types (void)
>> >    /* Poly types are a world of their own.  */
>> >    aarch64_simd_types[Poly8_t].eltype =
>aarch64_simd_types[Poly8_t].itype =
>> >      build_distinct_type_copy (unsigned_intQI_type_node);
>> > +  TYPE_STRING_FLAG (aarch64_simd_types[Poly8_t].eltype) = false;
>> >    aarch64_simd_types[Poly16_t].eltype =
>> > aarch64_simd_types[Poly16_t].itype =
>> >      build_distinct_type_copy (unsigned_intHI_type_node);
>> >    aarch64_simd_types[Poly64_t].eltype =
>> > aarch64_simd_types[Poly64_t].itype =
>
>This fix seems correct to me, the poly types are not strings. Looking
>at
>other uses of TYPE_STRING_FLAG this change doesn't seem like it would
>have
>impact on parsing or code generation.
>
>OK for trunk.
>
>> >>> A second set of tests fail due to changed inlining behaviour for
>> >>> functions
>> >>> with char array initialization:
>> >>>
>> >>>   gcc.target/aarch64/vset_lane_1.c
>> >>>   gcc.target/aarch64/vneg_s.c
>> >>>   gcc.target/aarch64/vclz.c
>> >>
>> >> I'm not sure what's going on here.  The tests are very big and
>> >> take forever to compile with an aarch64 cross-compiler, and I'm
>> >> not sure what to look for.  Can you provide a smaller test case
>> >> that shows the issue?
>> 
>> I wonder if these changes might be due to the same problem:
>> the tests define and initialize arrays of the Int8x16_t type
>> which is initialized to intQI_type_node, i.e., the signed
>> form of Poly8_t.  Does the conversion to STRING_CST cause
>> a performance degradation or is it just that the tests end
>> up with equivalent but slightly different assembly?
>
>These tests aren't looking at performance, just expecting to see
>certain
>instructions emitted. The only change is that now the int8x16_t forms
>are
>inlined (so the scan-assembler-times fails with two matches, one
>expected,
>one in the inlined function body copy).
>
>The difference seems to be in the initialization cost of the input data
>set.
>
>Before your patch:
>
>  int8_tD.3359 test_set0D.21541[8];
>  int8_tD.3359 answ_set0D.21542[8];
>
>      test_set0D.21541[0] = 0;
>      test_set0D.21541[1] = 1;
>      test_set0D.21541[2] = -1;
>      test_set0D.21541[3] = 10;
>      test_set0D.21541[4] = -10;
>      test_set0D.21541[5] = 0;
>      test_set0D.21541[6] = 127;
>      test_set0D.21541[7] = -128;
>      answ_set0D.21542[0] = 0;
>      answ_set0D.21542[1] = -1;
>      answ_set0D.21542[2] = 1;
>      answ_set0D.21542[3] = -10;
>      answ_set0D.21542[4] = 10;
>      answ_set0D.21542[5] = 0;
>      answ_set0D.21542[6] = -127;
>      answ_set0D.21542[7] = -128;
>
>After your patch:
>
>  int8_tD.3357 test_set0D.21539[8];
>  int8_tD.3357 answ_set0D.21540[8];
>
>      test_set0D.21539 = "";
>      answ_set0D.21540 = "";

Can we fix printing of string literals to include non-printable chars please? The above looks like wrong-code though it probably isn't. When Martin L. proposed a similar patch I was suggesting to restrict conversion to initializes with only printable characters. 

>I think that is probably what you expected to happen; but the impact on
>inlining might not have been.

It's more the effect of changed gimplification that shows, the inlining is a 2nd order effect. 

Richard. 

 Probably, we want to just change these
>tests
>to explicitly disable inlining. The tests appear to execute correctly.
>
>The print in the dump file is a bit unusual; presumably the impact of
>having
>non-printing characters in my initializer list - but less helpful
>output for
>it.
>
>Off topic; these tests are quick to copmpile on my cross and native
>compilers. Do you have additional checking enabled?
>
>Thanks,
>James
>
>> 
>> The tests also use int8_t and uint8_t for the expected results.
>> Those are typedefs for signed and unsigned char, respectively.
>> Is the conversion to strings for those fine?
>> 
>> Martin