On Thu, 2018-08-09 at 08:53 -0500, Bill Schmidt wrote:
> > On Aug 7, 2018, at 2:25 PM, Will Schmidt <will_schm...@vnet.ibm.com> wrote:
> >
> > Hi
> > Enable GIMPLE folding of the vec_splat() intrinsic.
> >
> > For review.. feedback is expected. :-)
> >
> > I came up with the following after spending some time poking around
> > at the tree_vec_extract() and vector_element() functions as seen
> > in tree-vect-generic.c looking for insights. Some of this seems a
> > bit clunky to me yet, but this is functional as far as make-check
> > can tell, and is as far as I can get without additional input.
> >
> > This uses the tree_vec_extract() function out of tree-vect-generic.c
> > to retrieve the splat value, which is a BIT_FIELD_REF. That function is
> > made non-static as part of this change.
> >
> > In review of the .gimple output, this folding takes a sample testcase
> > of
> > vector bool int testb_0 (vector bool int x)
> > {
> > return vec_splat (x, 0b00000);
> > }
> > from:
> > testb_0 (__vector __bool int x)
> > {
> > __vector __bool intD.1486 D.2855;
> >
> > _1 = VIEW_CONVERT_EXPR<__vector signed intD.1468>(xD.2778);
> > _2 = __builtin_altivec_vspltwD.1919 (_1, 0);
> > D.2855 = VIEW_CONVERT_EXPR<__vector __bool intD.1486>(_2);
> > return D.2855;
> > }
> > to:
> > testb_0 (__vector __bool int x)
> > {
> > __vector __bool intD.1486 D.2855;
> >
> > _1 = VIEW_CONVERT_EXPR<__vector signed intD.1468>(xD.2778);
> > D.2856 = BIT_FIELD_REF <_1, 32, 0>;
> > _2 = {D.2856, D.2856, D.2856, D.2856};
> > D.2855 = VIEW_CONVERT_EXPR<__vector __bool intD.1486>(_2);
> > return D.2855;
> > }
> >
> This looks okay.
> >
> > Testcases are being posted as a separate patch.
> >
> > OK for trunk?
> > Thanks,
> > -Will
> >
> > [gcc]
> >
> > 2018-08-07 Will Schmidt <will_schm...@vnet.ibm.com>
> >
> > * config/rs6000/rs6000.c (rs6000_gimple_fold_builtin): Add support for
> > early gimple folding of vec_splat().
> > * tree-vect-generic.c: Remove static from tree_vec_extract() definition.
> > * gimple-fold.h: Add an extern define for tree_vec_extract().
> >
> > diff --git a/gcc/config/rs6000/rs6000.c b/gcc/config/rs6000/rs6000.c
> > index 35c32be..acc6b49 100644
> > --- a/gcc/config/rs6000/rs6000.c
> > +++ b/gcc/config/rs6000/rs6000.c
> > @@ -15764,10 +15764,56 @@ rs6000_gimple_fold_builtin (gimple_stmt_iterator
> > *gsi)
> > tree splat_tree = build_vector_from_val (TREE_TYPE (lhs), splat_value);
> > g = gimple_build_assign (lhs, splat_tree);
> > gimple_set_location (g, gimple_location (stmt));
> > gsi_replace (gsi, g, true);
> > return true;
> > + }
> > +
> > + /* Flavors of vec_splat. */
> > + // a = vec_splat (b, 0x3) ; // a = { b[3],b[3],b[3],...};
> > + case ALTIVEC_BUILTIN_VSPLTB:
> > + case ALTIVEC_BUILTIN_VSPLTH:
> > + case ALTIVEC_BUILTIN_VSPLTW:
> > + case VSX_BUILTIN_XXSPLTD_V2DI:
> > + case VSX_BUILTIN_XXSPLTD_V2DF:
> > + {
> > + arg0 = gimple_call_arg (stmt, 0); /* input vector. */
> > + arg1 = gimple_call_arg (stmt, 1); /* index into arg0. */
> > + /* Only fold the vec_splat_*() if arg1 is a constant
> > + 5-bit unsigned literal. */
> > + if (TREE_CODE (arg1) != INTEGER_CST || TREE_INT_CST_LOW (arg1) > 0x1f)
> > + return false;
> > +
> > + lhs = gimple_call_lhs (stmt);
> > + tree lhs_type = TREE_TYPE (lhs);
> > +
> > + tree splat;
> > + if (TREE_CODE (arg0) == VECTOR_CST)
> > + splat = VECTOR_CST_ELT (arg0, TREE_INT_CST_LOW (arg1));
>
> You should force arg1 into range before this. It should be adjusted modulo
> VECTOR_CST_NELTS (arg0). Yes, the underlying vsplt* instructions will
OK.
> handle the modulo itself, but when expanding early we should make the
> correction early, else something is likely to explode. Do you have a test
> where arg1 is less than 32 but greater than the number of elements?
Almost. :-) I test for arg1 < 32 and > #elms, but not with the
arg0-is-constant scenario. I'll craft up a couple more testcases for
that.
>
> > + else
> > + {
> > + /* Determine (in bits) the length and start location of the
> > + splat value for a call to the tree_vec_extract helper. */
> > + int tree_size_in_bits = TREE_INT_CST_LOW (size_in_bytes (lhs_type))
> > + * BITS_PER_UNIT;
>
> I expect you should use arg0's type rather than lhs_type here. They
> should be the same, of course; it's just clearer.
ok.
>
> > + int splat_elem_size = tree_size_in_bits / VECTOR_CST_NELTS (arg0);
> > + int splat_start_bit = TREE_INT_CST_LOW (arg1) * splat_elem_size;
> > + /* Do not attempt to early-fold if the size + specified offset into
> > + the vector would touch outside of the source vector. */
> > + if ((splat_start_bit + splat_elem_size) > tree_size_in_bits)
> > + return false;
>
> This won't be necessary once you fix the modulo issue.
ok.
> The rest LGTM.
thanks for the review and feedback. :-)
-Will
>
> Thanks,
> Bill
>
> > + tree len = build_int_cst (bitsizetype, splat_elem_size);
> > + tree start = build_int_cst (bitsizetype, splat_start_bit);
> > + splat = tree_vec_extract (gsi, TREE_TYPE (lhs_type), arg0,
> > + len, start);
> > + }
> > + /* And finally, build the new vector. */
> > + tree splat_tree = build_vector_from_val (lhs_type, splat);
> > + g = gimple_build_assign (lhs, splat_tree);
> > + gimple_set_location (g, gimple_location (stmt));
> > + gsi_replace (gsi, g, true);
> > + return true;
> > }
> >
> > /* vec_mergel (integrals). */
> > case ALTIVEC_BUILTIN_VMRGLH:
> > case ALTIVEC_BUILTIN_VMRGLW:
> > diff --git a/gcc/gimple-fold.h b/gcc/gimple-fold.h
> > index 04e9bfa..e634180 100644
> > --- a/gcc/gimple-fold.h
> > +++ b/gcc/gimple-fold.h
> > @@ -59,10 +59,11 @@ extern tree gimple_fold_indirect_ref (tree);
> > extern bool gimple_fold_builtin_sprintf (gimple_stmt_iterator *);
> > extern bool gimple_fold_builtin_snprintf (gimple_stmt_iterator *);
> > extern bool arith_code_with_undefined_signed_overflow (tree_code);
> > extern gimple_seq rewrite_to_defined_overflow (gimple *);
> > extern void replace_call_with_value (gimple_stmt_iterator *, tree);
> > +extern tree tree_vec_extract (gimple_stmt_iterator *, tree, tree, tree,
> > tree);
> >
> > /* gimple_build, functionally matching fold_buildN, outputs stmts
> > int the provided sequence, matching and simplifying them on-the-fly.
> > Supposed to replace force_gimple_operand (fold_buildN (...), ...). */
> > extern tree gimple_build (gimple_seq *, location_t,
> > diff --git a/gcc/tree-vect-generic.c b/gcc/tree-vect-generic.c
> > index 909f790..1c9701d 100644
> > --- a/gcc/tree-vect-generic.c
> > +++ b/gcc/tree-vect-generic.c
> > @@ -118,11 +118,11 @@ build_word_mode_vector_type (int nunits)
> >
> > typedef tree (*elem_op_func) (gimple_stmt_iterator *,
> > tree, tree, tree, tree, tree, enum tree_code,
> > tree);
> >
> > -static inline tree
> > +tree
> > tree_vec_extract (gimple_stmt_iterator *gsi, tree type,
> > tree t, tree bitsize, tree bitpos)
> > {
> > if (TREE_CODE (t) == SSA_NAME)
> > {
> >
> >
>
