[Bug target/96373] SVE miscompilation on vectorized division loop, leading to FP exception

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96373

--- Comment #16 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The trunk branch has been updated by Richard Sandiford <rsandifo@gcc.gnu.org>:

https://gcc.gnu.org/g:b9c78605039f839f3c79ad8fca4f60ea9a5654ed

commit r13-5979-gb9c78605039f839f3c79ad8fca4f60ea9a5654ed
Author: Richard Sandiford <richard.sandiford@arm.com>
Date:   Tue Feb 14 09:18:07 2023 +0000

    vect: Make partial trapping ops use predication [PR96373]

    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.c.

    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.

    gcc/
            PR tree-optimization/96373
            * tree-vect-stmts.cc (vectorizable_operation): Predicate trapping
            operations on the loop mask.  Reject partial vectors if this isn't
            possible.

    gcc/testsuite/
            PR tree-optimization/96373
            PR tree-optimization/108571
            * gcc.target/aarch64/sve/fabd_1.c: Add -fno-trapping-math.
            * gcc.target/aarch64/sve/fsubr_1.c: Likewise.
            * gcc.target/aarch64/sve/fmul_1.c: Expect predicate ops.
            * gcc.target/aarch64/sve/fp_arith_1.c: Likewise.