> 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
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?
> + 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.
> + 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.
The rest LGTM.
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)
> {
>
>
