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From: "yyc1992 at gmail dot com" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug target/106324] New: ptrue not reused between vector
 instructions and predicate instructions
Date: Sat, 16 Jul 2022 13:05:50 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D106324

            Bug ID: 106324
           Summary: ptrue not reused between vector instructions and
                    predicate instructions
           Product: gcc
           Version: 12.1.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: target
          Assignee: unassigned at gcc dot gnu.org
          Reporter: yyc1992 at gmail dot com
  Target Milestone: ---

The following code has two use of `svptrue_b64()`s and none of the instruct=
ions
using them should be clearning it so only one `ptrue` instruction should be
needed.

```
svfloat64_t test(svbool_t pg, svfloat64_t a, svfloat64_t b)
{
    auto d =3D svdiv_m(svptrue_b64(), a, b);
    return svmul_m(svnot_z(svptrue_b64(), pg), d, d);
}
```

However, the code generated is,

```
        ptrue   p2.b, all
        ptrue   p1.d, all
        fdiv    z0.d, p2/m, z0.d, z1.d
        not     p0.b, p1/z, p0.b
        fmul    z0.d, p0/m, z0.d, z0.d
        ret
```

which has an extra `ptrue`.

OTOH, clang generates,

```
        ptrue   p1.d
        fdiv    z0.d, p1/m, z0.d, z1.d
        not     p0.b, p1/z, p0.b
        fmul    z0.d, p0/m, z0.d, z0.d
        ret
```

and the same `ptrue` is reused in both instructions.

This seems to be caused by gcc insisting on using `svptrue_b8` for the svnot
which does not seem necessary here especially since _b64 is explicitly
requested. Changing svptrue_b64 to svptrue_b8 in the code fixes the issue.=