Re: [PATCH, rs6000] Gimple folding for vec_madd()

[Will Schmidt <will_schmidt at vnet dot ibm dot com>]

On Thu, 2017-10-26 at 11:05 +0200, Richard Biener wrote:
> On Wed, Oct 25, 2017 at 4:38 PM, Will Schmidt <will_schmidt@vnet.ibm.com> wrote:
> > Hi,
> >
> > Add support for gimple folding of the vec_madd() (vector multiply-add)
> > intrinsics.
> > Testcase coverage is provided by the existing tests
> >  gcc.target/powerpc/fold-vec-madd-*.c
> >
> > Sniff-tests appear clean.  A full regtest is currently running across assorted Power systems. (P6-P9).
> > OK for trunk (pending clean run results)?
> 
> You can use FMA_EXPR on integer operands as well.  Otherwise you risk
> the FMA be not matched by combine later when part of the operation is
> CSEd.

I had tried that initially, without success,..   I'll probably need
another hint.  :-) 
Looking a bit closer, I think I see why the assert fired, but I'm not
sure what the proper fix would be.

So attempting to the FMA_EXPR on the integer operands. (vector shorts in
this case), I end up triggering this error:

/home/willschm/gcc/gcc-mainline-vec_fold_misc/gcc/testsuite/gcc.target/powerpc/fold-vec-madd-short.c:14:10: internal compiler error: in expand_expr_real_2, at expr.c:8712
0x10813303 expand_expr_real_2(separate_ops*, rtx_def*, machine_mode, expand_modifier)
	/home/willschm/gcc/gcc-mainline-vec_fold_misc/gcc/expr.c:8712
0x1081822f expand_expr_real_1(tree_node*, rtx_def*, machine_mode, expand_modifier, rtx_def**, bool)
	/home/willschm/gcc/gcc-mainline-vec_fold_misc/gcc/expr.c:9787
0x1080f7bb expand_expr_real(tree_node*, rtx_def*, machine_mode, expand_modifier, rtx_def**, bool)
	/home/willschm/gcc/gcc-mainline-vec_fold_misc/gcc/expr.c:8084
...


which when followed back, I tripped an assert here:  (gcc/expr.c:
expand_expr_real_2() ~ line 8710)

    case FMA_EXPR:
      {
	optab opt = fma_optab;
	gimple *def0, *def2;
	if (optab_handler (fma_optab, mode) == CODE_FOR_nothing)
	  {
	    tree fn = mathfn_built_in (TREE_TYPE (treeop0), BUILT_IN_FMA);
	    tree call_expr;

	    gcc_assert (fn != NULL_TREE);

where gcc/builtins.c
mathfn_built_in()->mathfn_built_in_1->mathfn_built_in_2 looks to have
returned END_BUILTINS/NULL_TREE, due to falling through the if/else
tree:

  if (TYPE_MAIN_VARIANT (type) == double_type_node)
    return fcode;
  else if (TYPE_MAIN_VARIANT (type) == float_type_node)
    return fcodef;
  else if (TYPE_MAIN_VARIANT (type) == long_double_type_node)
    return fcodel;
  else
    return END_BUILTINS;

Looks like that is all double/float/long double contents.  First blush
attempt would be to add V8HI_type_node/integer_type_node to that if/else
tree, but that doesn't look like it would be near enough.

Thanks
-Will

> 
> Richard.
> 
> > Thanks,
> > -Will
> >
> > [gcc]
> >
> > 2017-10-25  Will Schmidt <will_schmidt@vnet.ibm.com>
> >
> >         * config/rs6000/rs6000.c: (rs6000_gimple_fold_builtin) Add support for
> >           gimple folding of vec_madd() intrinsics.
> >
> > diff --git a/gcc/config/rs6000/rs6000.c b/gcc/config/rs6000/rs6000.c
> > index 4837e14..04c2b15 100644
> > --- a/gcc/config/rs6000/rs6000.c
> > +++ b/gcc/config/rs6000/rs6000.c
> > @@ -16606,10 +16606,43 @@ rs6000_gimple_fold_builtin (gimple_stmt_iterator *gsi)
> >                                            build_int_cst (arg2_type, 0)), arg0);
> >          gimple_set_location (g, loc);
> >          gsi_replace (gsi, g, true);
> >          return true;
> >        }
> > +
> > +    /* vec_madd (Float) */
> > +    case ALTIVEC_BUILTIN_VMADDFP:
> > +    case VSX_BUILTIN_XVMADDDP:
> > +      {
> > +       arg0 = gimple_call_arg (stmt, 0);
> > +       arg1 = gimple_call_arg (stmt, 1);
> > +       tree arg2 = gimple_call_arg (stmt, 2);
> > +       lhs = gimple_call_lhs (stmt);
> > +       gimple *g = gimple_build_assign (lhs, FMA_EXPR , arg0, arg1, arg2);
> > +       gimple_set_location (g, gimple_location (stmt));
> > +       gsi_replace (gsi, g, true);
> > +       return true;
> > +      }
> > +    /* vec_madd (Integral) */
> > +    case ALTIVEC_BUILTIN_VMLADDUHM:
> > +      {
> > +       arg0 = gimple_call_arg (stmt, 0);
> > +       arg1 = gimple_call_arg (stmt, 1);
> > +       tree arg2 = gimple_call_arg (stmt, 2);
> > +       lhs = gimple_call_lhs (stmt);
> > +       tree lhs_type = TREE_TYPE (lhs);
> > +       location_t loc = gimple_location (stmt);
> > +       gimple_seq stmts = NULL;
> > +       tree mult_result = gimple_build (&stmts, loc, MULT_EXPR,
> > +                                      lhs_type, arg0, arg1);
> > +       tree plus_result = gimple_build (&stmts, loc, PLUS_EXPR,
> > +                                      lhs_type, mult_result, arg2);
> > +       gsi_insert_seq_before (gsi, stmts, GSI_SAME_STMT);
> > +       update_call_from_tree (gsi, plus_result);
> > +       return true;
> > +      }
> > +
> >      default:
> >         if (TARGET_DEBUG_BUILTIN)
> >            fprintf (stderr, "gimple builtin intrinsic not matched:%d %s %s\n",
> >                     fn_code, fn_name1, fn_name2);
> >        break;
> >
> >
>