[PATCH, AArch64] Enable shrink wrap

[Andrew Pinski]

On Tue, Sep 23, 2014 at 2:51 PM, Jiong Wang
<wong.kwongyuan.tools@gmail.com> wrote:
> 2014-09-23 21:59 GMT+01:00 Sebastian Pop <sebpop@gmail.com>:
>> Marcus Shawcroft wrote:
>>> On 4 September 2014 15:14, Jiong Wang <jiong.wang@arm.com> wrote:
>>> > this patch enabled stack shrink-wrap support on AArch64.
>>> >
>>> > no regression on aarch64-none-elf bare-metal.
>>> > aarch64 bootstrap OK.
>>> >
>>> > ok to install?
>>> >
>>> > 2014-09-04 Renlin Li<renlin.li@arm.com>
>>> >
>>> > gcc/
>>> >   * config/aarch64/aarch64.md (return): New expand.
>>> >   (simple_return): Likewise.
>>> >   * config/aarch64/aarch64.c (aarch64_use_return_insn_p): New function.
>>> >   * config/aarch64/aarch64-protos.h (aarch64_use_return_insn_p): New
>>> > declaration.
>>> >
>>> > gcc/testsuite
>>> >   * gcc.dg/ira-shrinkwrap-prep-1.c: Enable aarch64.
>>> >   * gcc.dg/ira-shrinkwrap-prep-2.c: Likewise.
>>> >   * gcc.dg/pr10474.c: Likewise.
>>>
>>> OK, committed as 215508
>>> /Marcus
>>
>> This patch causes a regression when compiling this testcase with -O2 and above:
>>
>> void mm(double** A, double** B, double** C, unsigned N, unsigned S)
>> {
>>   unsigned i, j, k;
>>
>>   for (i = 0; i < N; i += S) {
>>     for (j = 0; j < N; j += S) {
>>       for (k = 0; k < N; k += S) {
>>
>>         unsigned ib = (N) < ((i + S)) ? N : (i + S);
>>         unsigned jb = (N) < ((j + S)) ? N : (j + S);
>>         unsigned kb = (N) < ((k + S)) ? N : (k + S);
>>         unsigned i0, j0, k0;
>>
>>         for (i0 = i; i0 < ib; i0++) {
>>           for (j0 = j; j0 < jb; j0++) {
>>             double* a = A[i0];
>>             double* b = B[j0];
>>             double scratch = C[i0][j0];
>>             for (k0 = k; k0 < kb; k0++) {
>>               scratch += a[k0] * b[k0];
>>             }
>>             C[i0][j0] = scratch;
>>           }
>>         }
>>       }
>>     }
>>   }
>>   asm volatile ("bar:");
>> }
>>
>> $ aarch64-gcc -O2 mm.c -S -o - | grep 'bar:' | wc -l
>> 2
>> $ aarch64-gcc -O1 mm.c -S -o - | grep 'bar:' | wc -l
>> 1
>
> Interesting.
>
> I have done a quick investigation on x86/mips/arm32/aarch64 and found
>
>   * x86/mips couldn't shrink wrap this function.
>   * arm32/aarch64 could shrink wrap it.
>     but both generate the same code layout, with redundant exit basic block.
>
> So, looks like it's caused by some hiding issue in generic code.


There is no bug here.  inline-asm can be duplicated (I thought this
was documented too).

See https://gcc.gnu.org/bugzilla/show_bug.cgi?id=20468 also.

Thanks,
Andrew

>
>>
>> Thanks,
>> Sebastian