Hi Richard,

on 2023/1/27 19:08, Richard Sandiford via Gcc-patches wrote:
> PR96373 points out that a predicated SVE loop currently converts
> trapping unconditional ops into unpredicated vector ops.  Doing
> the operation on inactive lanes can then raise an exception.
> 
> As discussed in the PR trail, we aren't 100% consistent about
> whether we preserve traps or not.  But the direction of travel
> is clearly to improve that rather than live with it.  This patch
> tries to do that for the SVE case.
> 
> Doing this regresses gcc.target/aarch64/sve/fabd_1.c.  I've added
> -fno-trapping-math for now and filed PR108571 to track it.
> A similar problem applies to fsubr_1.d.
> 
> I think this is likely to regress Power 10, since conditional
> operations are only available for masked loops.  I think we'll
> need to add -fno-trapping-math to any affected testcases,
> but I don't have a Power 10 system to test on.  Kewen, would you
> mind giving this a spin and seeing how bad the fallout is?
> 

Sorry for the late reply, I'm just back from vacation.

Thank you for fixing this and caring about Power10!

I tested your proposed patch on one Power10 machine (ppc64le),
it's bootstrapped but some test failures got exposed as below.

< FAIL: gcc.target/powerpc/p9-vec-length-epil-1.c scan-assembler-times \\\\mlxvl\\\\M 14
< FAIL: gcc.target/powerpc/p9-vec-length-epil-1.c scan-assembler-times \\\\mstxvl\\\\M 7
< FAIL: gcc.target/powerpc/p9-vec-length-epil-2.c scan-assembler-times \\\\mlxvl\\\\M 20
< FAIL: gcc.target/powerpc/p9-vec-length-epil-2.c scan-assembler-times \\\\mstxvl\\\\M 10
< FAIL: gcc.target/powerpc/p9-vec-length-epil-3.c scan-assembler-times \\\\mlxvl\\\\M 14
< FAIL: gcc.target/powerpc/p9-vec-length-epil-3.c scan-assembler-times \\\\mstxvl\\\\M 7
< FAIL: gcc.target/powerpc/p9-vec-length-epil-4.c scan-assembler-times \\\\mlxvl\\\\M 70
< FAIL: gcc.target/powerpc/p9-vec-length-epil-4.c scan-assembler-times \\\\mlxvx?\\\\M 120
< FAIL: gcc.target/powerpc/p9-vec-length-epil-4.c scan-assembler-times \\\\mstxvl\\\\M 70
< FAIL: gcc.target/powerpc/p9-vec-length-epil-4.c scan-assembler-times \\\\mstxvx?\\\\M 70
< FAIL: gcc.target/powerpc/p9-vec-length-epil-5.c scan-assembler-times \\\\mlxvl\\\\M 21
< FAIL: gcc.target/powerpc/p9-vec-length-epil-5.c scan-assembler-times \\\\mstxvl\\\\M 21
< FAIL: gcc.target/powerpc/p9-vec-length-epil-5.c scan-assembler-times \\\\mstxvx?\\\\M 21
< FAIL: gcc.target/powerpc/p9-vec-length-epil-6.c scan-assembler-times \\\\mlxvl\\\\M 10
< FAIL: gcc.target/powerpc/p9-vec-length-epil-6.c scan-assembler-times \\\\mlxvx?\\\\M 42
< FAIL: gcc.target/powerpc/p9-vec-length-epil-6.c scan-assembler-times \\\\mstxvl\\\\M 10
< FAIL: gcc.target/powerpc/p9-vec-length-epil-8.c scan-assembler-times \\\\mlxvl\\\\M 16
< FAIL: gcc.target/powerpc/p9-vec-length-epil-8.c scan-assembler-times \\\\mstxvl\\\\M 7
< FAIL: gcc.target/powerpc/p9-vec-length-full-1.c scan-assembler-not \\\\mlxvx\\\\M
< FAIL: gcc.target/powerpc/p9-vec-length-full-1.c scan-assembler-not \\\\mstxvx\\\\M
< FAIL: gcc.target/powerpc/p9-vec-length-full-1.c scan-assembler-times \\\\mlxvl\\\\M 20
< FAIL: gcc.target/powerpc/p9-vec-length-full-1.c scan-assembler-times \\\\mstxvl\\\\M 10
< FAIL: gcc.target/powerpc/p9-vec-length-full-2.c scan-assembler-not \\\\mlxvx\\\\M
< FAIL: gcc.target/powerpc/p9-vec-length-full-2.c scan-assembler-not \\\\mstxvx\\\\M
< FAIL: gcc.target/powerpc/p9-vec-length-full-2.c scan-assembler-times \\\\mlxvl\\\\M 20
< FAIL: gcc.target/powerpc/p9-vec-length-full-2.c scan-assembler-times \\\\mstxvl\\\\M 10
< FAIL: gcc.target/powerpc/p9-vec-length-full-3.c scan-assembler-times \\\\mlxvl\\\\M 14
< FAIL: gcc.target/powerpc/p9-vec-length-full-3.c scan-assembler-times \\\\mstxvl\\\\M 7
< FAIL: gcc.target/powerpc/p9-vec-length-full-4.c scan-assembler-not \\\\mlxvx\\\\M
< FAIL: gcc.target/powerpc/p9-vec-length-full-4.c scan-assembler-not \\\\mstxv\\\\M
< FAIL: gcc.target/powerpc/p9-vec-length-full-4.c scan-assembler-not \\\\mstxvx\\\\M
< FAIL: gcc.target/powerpc/p9-vec-length-full-4.c scan-assembler-times \\\\mlxvl\\\\M 70
< FAIL: gcc.target/powerpc/p9-vec-length-full-4.c scan-assembler-times \\\\mstxvl\\\\M 70
< FAIL: gcc.target/powerpc/p9-vec-length-full-5.c scan-assembler-not \\\\mlxvx\\\\M
< FAIL: gcc.target/powerpc/p9-vec-length-full-5.c scan-assembler-not \\\\mstxv\\\\M
< FAIL: gcc.target/powerpc/p9-vec-length-full-5.c scan-assembler-not \\\\mstxvx\\\\M
< FAIL: gcc.target/powerpc/p9-vec-length-full-5.c scan-assembler-times \\\\mlxvl\\\\M 21
< FAIL: gcc.target/powerpc/p9-vec-length-full-5.c scan-assembler-times \\\\mstxvl\\\\M 21
< FAIL: gcc.target/powerpc/p9-vec-length-full-6.c scan-assembler-times \\\\mlxvl\\\\M 10
< FAIL: gcc.target/powerpc/p9-vec-length-full-6.c scan-assembler-times \\\\mstxvl\\\\M 10
< FAIL: gcc.target/powerpc/p9-vec-length-full-6.c scan-assembler-times \\\\mstxvx?\\\\M 6
< FAIL: gcc.target/powerpc/p9-vec-length-full-8.c scan-assembler-times \\\\mlxvl\\\\M 30
< FAIL: gcc.target/powerpc/p9-vec-length-full-8.c scan-assembler-times \\\\mstxvl\\\\M 10

By checking several of them, it's due to that we don't vectorize
some loop having float type involved with partial vector any more.

As you suggested above, I fixed them with an extra option
"-fno-trapping-math" and verified all of them can pass again.
I also noticed that the original test case in PR96373 fails
on Power10 too, so I added one constructed case pr96373.c
into sub bucket gcc.target/powerpc for testing coverage
on Power.

One re-spin with the attached adjustment shows there is no
regression failure any more, and the new test case works well
on both ppc64 (P8) and ppc64le (P10) Linux.

BR,
Kewen
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