[Bug target/83920] [nvptx] bad predicate reset

["cesar at gcc dot gnu.org" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=83920

--- Comment #10 from cesar at gcc dot gnu.org ---
And here is the working code in -O2:

        {
                .reg.u32        %x;
                mov.u32 %x, %tid.x;
                setp.ne.u32     %r71, %x, 0;
        }
        @%r71   bra     $L13;
                mov.u64 %r45, %ar0;
                mov.u64 %r46, %ar1;
                mov.u32 %r42, %ctaid.x;
                shl.b32 %r48, %r42, 2;
                add.u32 %r37, %r48, %r42;
                mov.u32 %r31, 5;
                setp.ne.u64     %r64, %r46, 1;
                mov.u32 %r66, 0;
$L13:
$L3:
                mov.pred        %r74, %r64;
                setp.eq.u32     %r64, 1, 0;
        @%r71   bra     $L12;
$L12:
                mov.pred        %r64, %r74;
                selp.u32        %r75, 1, 0, %r64;
                shfl.idx.b32    %r75, %r75, 0, 31;
                setp.ne.u32     %r64, %r75, 0;
        @%r64   bra.uni $L2;
$L6:

Notice how gcse's PRE pass hoisted the initialization of %r64 early in the
entry block.

I think we should go with my patch. If the register is live, it shouldn't
require your workaround.