Re: [PATCH, rs6000] xfail float128 comparison test case that fails on powerpc64 [PR108728]

["Kewen.Lin" <linkw@linux.ibm.com>]

Hi Haochen,

on 2023/4/14 09:34, HAO CHEN GUI wrote:
> Hi Kewen,
> 
> 在 2023/4/13 16:32, Kewen.Lin 写道:
>> xfail all powerpc*-*-* can have some XPASSes on those ENVs with
>> software emulation.  Since the related hw insn xscmpuqp is guarded
>> with TARGET_FLOAT128_HW, could we use the effective target
>> ppc_float128_hw instead?
> 
> Thanks for your review comments. It's tricky. It invokes "__lekf2"
> with "-mno-float128_hw". But it doesn't always pass the check.
> With math library on P8, it can. With the library on P9, it fails.

Math library doesn't provide it, __lekf2 is from libgcc (GCC itself).
The reason why the __lekf2 behaves differently on P8 and P9 is that
we have SW and HW versions for __lekf2, when the underlying "CPU
"supports 128-bit IEEE binary floating point instructions.", it will
use __lekf2_hw instead of __lekf2_sw, the former still adopts
insn xscmpuqp, then it fails.

> So it's totally depended on the version of library which is not
> controlled by GCC. What's your opinion?

So 
1) for ppc_float128_hw, it generates xscmpuqp then fails.
2) for !ppc_float128_hw, it uses __lekf2 but the underlying ENV
   supports __builtin_cpu_supports ("ieee128"), it exploits
   xscmpuqp, then fails.

Ideally we should use one effective target like ppc_ieee128_hw to
indicate the underlying ENV supports __builtin_cpu_supports ("ieee128")
but I think it may not be worth to adding that at this stage, so
I'd suggest xfail-ing it for "ppc_float128_hw || (ppc_cpu_supports_hw && p9vector_hw)".

BR,
Kewen

> 
> Test result on P9
> make check-gcc-c RUNTESTFLAGS="--target_board=unix'{-mno-float128-hardware}' dg-torture.exp=float128-cmp-invalid.c"
> 
> FAIL: gcc.dg/torture/float128-cmp-invalid.c   -O0  execution test
> FAIL: gcc.dg/torture/float128-cmp-invalid.c   -O1  execution test
> FAIL: gcc.dg/torture/float128-cmp-invalid.c   -O2  execution test
> FAIL: gcc.dg/torture/float128-cmp-invalid.c   -O3 -g  execution test
> FAIL: gcc.dg/torture/float128-cmp-invalid.c   -Os  execution test
> FAIL: gcc.dg/torture/float128-cmp-invalid.c   -O2 -flto -fno-use-linker-plugin -flto-partition=none  execution test
> FAIL: gcc.dg/torture/float128-cmp-invalid.c   -O2 -flto -fuse-linker-plugin -fno-fat-lto-objects  execution test
> 
>                 === gcc Summary ===
> 
> # of expected passes            7
> # of unexpected failures        7
> 
> Gui Haochen
> Thanks