On 8/20/18 4:44 PM, Will Schmidt wrote:
> Hi
> Enable GIMPLE folding of the vec_splat() intrinsic. (v3).
>
> 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.
>
> Testcases are already in-tree.
>
> V2 updates, per feedback previously received.
> Forced arg1 into range (modulo #elements) before attempting to extract
> the splat value.
> Removed the (now unnecessary) code that did bounds-checking before calling
> the tree_vec_extract helper.
> Used arg0_type rather than lhs_type for calculating the tree size.
>
> V3 updates, inspired by additional offline discussion with Segher.
> Noting that for vec_splat(arg1,arg2), the ABI describes ARG2 as an element
> number less than the number of elements supported by the respective ARG1
> type, so we do not attempt to gimple-fold the intrinsic if we determine our
> value is out of range. Thus, the initial check ensures that ARG1 is both
> constant and has a valid index into ARG0.
> The subsequent modulo operation is no longer necessary, and has been removed.
> Also eliminated a few now-unused variables.
>
> Sniff-tests pass. full regtest against powerpc platforms is in the queue.
> OK for trunk with passing test results?
>
> Thanks,
> -Will
>
> [gcc]
>
> 2018-08-20 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 5f77afd..4c3257f 100644
> --- a/gcc/config/rs6000/rs6000.c
> +++ b/gcc/config/rs6000/rs6000.c
> @@ -15768,10 +15768,52 @@ 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) becomes 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 both a constant value, and a
> valid
> + index into the arg0 vector. */
> + unsigned int n_elts = VECTOR_CST_NELTS (arg0);
> + if (TREE_CODE (arg1) != INTEGER_CST
> + || TREE_INT_CST_LOW (arg1) > (n_elts -1))
Space between - and 1.
I'm still not convinced we should do this. The semantics of vec_splat are
to select the element as arg1 modulo n_elts. Odd as it seems, it's historically
valid for values between 0 and 31 to be used regardless of the value of n_elts.
Since arg1 is a constant we can easily bring it into valid range and expand it
early, rather than losing optimization opportunities by keeping this as a
built-in call.
Do we have test cases for arg1 in {n_elts, ..., 31}? What's GCC's current
behavior? Maybe we already aren't honoring this technically legal case?
If so, it doesn't matter. (I think we may have had this discussion on IRC
but I have lost track of it. Doesn't hurt to have it again in a permanent
location. ;-)
Otherwise looks fine to me, though of course I can't approve.
Thanks,
Bill
> + return false;
> + lhs = gimple_call_lhs (stmt);
> + tree lhs_type = TREE_TYPE (lhs);
> + tree arg0_type = TREE_TYPE (arg0);
> + tree splat;
> + if (TREE_CODE (arg0) == VECTOR_CST)
> + splat = VECTOR_CST_ELT (arg0, TREE_INT_CST_LOW (arg1));
> + else
> + {
> + /* Determine (in bits) the length and start location of the
> + splat value for a call to the tree_vec_extract helper. */
> + int splat_elem_size = TREE_INT_CST_LOW (size_in_bytes (arg0_type))
> + * BITS_PER_UNIT / n_elts;
> + int splat_start_bit = TREE_INT_CST_LOW (arg1) * splat_elem_size;
> + 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)
> {
>
>
