[Bug target/112363] New: GCN: 'FAIL: gcc.dg/vect/vect-cond-reduc-in-order-2-signed-zero.c execution test'

[Bug target/112363] New: GCN: 'FAIL: gcc.dg/vect/vect-cond-reduc-in-order-2-signed-zero.c execution test'

[tschwinge at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=112363

            Bug ID: 112363
           Summary: GCN: 'FAIL:
                    gcc.dg/vect/vect-cond-reduc-in-order-2-signed-zero.c
                    execution test'
           Product: gcc
           Version: 14.0
            Status: UNCONFIRMED
          Keywords: testsuite-fail
          Severity: normal
          Priority: P3
         Component: target
          Assignee: unassigned at gcc dot gnu.org
          Reporter: tschwinge at gcc dot gnu.org
                CC: ams at gcc dot gnu.org, jules at gcc dot gnu.org
  Target Milestone: ---
            Target: GCN

For GCN target (tested '-march=gfx90a'), the
'gcc.dg/vect/vect-cond-reduc-in-order-2-signed-zero.c' recently added with
PR111401 commit r14-5076-g01c18f58d37865d5f3bbe93e666183b54ec608c7 "ifcvt/vect:
Emit COND_OP for conditional scalar reduction" FAILs its execution test:

    '[...]/build-gcc/gcc/gcn-run'
'./vect-cond-reduc-in-order-2-signed-zero.exe'; echo XYZ$?ZYX
    GCN Kernel Aborted
    Kernel aborted
    XYZ134ZYX
    OK> 
    Elapsed time: 199 ms
    FAIL: gcc.dg/vect/vect-cond-reduc-in-order-2-signed-zero.c execution test

As that commit and test case does mention "signed zero", maybe that's where the
problem lies?

[Bug target/112363] GCN: 'FAIL: gcc.dg/vect/vect-cond-reduc-in-order-2-signed-zero.c execution test'

[rdapp at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=112363

--- Comment #1 from Robin Dapp <rdapp at gcc dot gnu.org> ---
This test was introduced in order to check that we correctly "reduce" with -0.0
as neutral element, i.e. a reduction preserves an intial -0.0 and doesn't turn
it into 0.0 by adding 0.0.  Kernel aborted means an assertion failed?  Or
something else?

[Bug target/112363] GCN: 'FAIL: gcc.dg/vect/vect-cond-reduc-in-order-2-signed-zero.c execution test'

[tschwinge at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=112363

--- Comment #2 from Thomas Schwinge <tschwinge at gcc dot gnu.org> ---
Right, that's what I suspected (see my "signed zero" comment).  And indeed, the
first check in 'main' instrumented as follows:

    --- gcc/testsuite/gcc.dg/vect/vect-cond-reduc-in-order-2-signed-zero.c
    +++ gcc/testsuite/gcc.dg/vect/vect-cond-reduc-in-order-2-signed-zero.c
    @@ -74,8 +74,11 @@ main ()
       double res4 = reduc_minus_double (a, -0.0, cond1, n);
       double ref4 = reduc_minus_double_ref (a, -0.0, cond1, n);

    +  __builtin_printf("L0\n");
    +  __builtin_printf("eq %d, SBres 0x%x, SBref 0x%x\n", res1 == ref1,
signbit (res1), signbit (ref1));
       if (res1 != ref1 || signbit (res1) != signbit (ref1))
         __builtin_abort ();
    +  __builtin_printf("L1\n");

..., I see:

    L0
    eq 1, SBres 0, SBref 80000000
    GCN Kernel Aborted
    Kernel aborted

..., so unexpected 'signbit' difference of '-0.0' '+' reduction, and thus
'abort'.  Thus, likely, a GCN target issue -- for Andrew/Julian to take over.