[Mesa-dev] [PATCH 16/26] i965: Implement the new imod and irem opcodes

[Jason Ekstrand]

On Tue, Mar 29, 2016 at 8:49 PM, Matt Turner <mattst88 at gmail.com> wrote:

> On Fri, Mar 25, 2016 at 4:12 PM, Jason Ekstrand <jason at jlekstrand.net>
> wrote:
> > ---
> >  src/mesa/drivers/dri/i965/brw_fs_nir.cpp   | 32
> ++++++++++++++++++++++++++++++
> >  src/mesa/drivers/dri/i965/brw_vec4_nir.cpp | 32
> ++++++++++++++++++++++++++++++
> >  2 files changed, 64 insertions(+)
> >
> > diff --git a/src/mesa/drivers/dri/i965/brw_fs_nir.cpp
> b/src/mesa/drivers/dri/i965/brw_fs_nir.cpp
> > index 14480fb..131f50e 100644
> > --- a/src/mesa/drivers/dri/i965/brw_fs_nir.cpp
> > +++ b/src/mesa/drivers/dri/i965/brw_fs_nir.cpp
> > @@ -844,8 +844,40 @@ fs_visitor::nir_emit_alu(const fs_builder &bld,
> nir_alu_instr *instr)
> >        unreachable("Should have been lowered by borrow_to_arith().");
> >
> >     case nir_op_umod:
> > +   case nir_op_irem:
> > +      /* According to the sign table for INT DIV in the Ivy Bridge PRM,
> it
> > +       * appears that our hardware just does the right thing for signed
> > +       * remainder.
> > +       */
> > +      bld.emit(SHADER_OPCODE_INT_REMAINDER, result, op[0], op[1]);
> > +      break;
> > +
> > +   case nir_op_imod: {
> > +      /* Get a regular C-style remainder.  If a % b == 0, set the
> predicate. */
> >        bld.emit(SHADER_OPCODE_INT_REMAINDER, result, op[0], op[1]);
> > +
> > +      /* Math instructions don't support conditional mod */
> > +      inst = bld.MOV(bld.null_reg_d(), result);
> > +      inst->conditional_mod = BRW_CONDITIONAL_NZ;
> > +
> > +      /* Now, we need to determine if signs of the sources are
> different.
> > +       * When we XOR the sources, the top bit is 0 if they are the same
> and 1
> > +       * if they are different.  We can then use a conditional modifier
> to
> > +       * turn that into a predicate.  This leads us to an XOR.l
> instruction.
> > +       */
> > +      fs_reg tmp = bld.vgrf(BRW_REGISTER_TYPE_D);
> > +      inst = bld.XOR(tmp, op[0], op[1]);
> > +      inst->predicate = BRW_PREDICATE_NORMAL;
> > +      inst->conditional_mod = BRW_CONDITIONAL_L;
>
> This goes against the PRM:
>
> "This operation does not produce sign or overflow conditions. Only the
> .e/.z or .ne/.nz conditional modifiers should be used."
>

D'oh...  I thought I'd fixed that.  I can add an AND.nz with 0x80000000
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