+2017-12-07 Richard Sandiford <richard.sandiford@arm.com>
+
+ * doc/generic.texi (VECTOR_CST): Describe new representation of
+ vector constants.
+ * vector-builder.h: New file.
+ * tree-vector-builder.h: Likewise.
+ * tree-vector-builder.c: Likewise.
+ * Makefile.in (OBJS): Add tree-vector-builder.o.
+ * tree.def (VECTOR_CST): Update comment to refer to generic.texi.
+ * tree-core.h (tree_base): Add a vector_cst field to the u union.
+ (tree_vector): Change the number of elements to
+ vector_cst_encoded_nelts.
+ * tree.h (VECTOR_CST_NELTS): Redefine using TYPE_VECTOR_SUBPARTS.
+ (VECTOR_CST_ELTS): Delete.
+ (VECTOR_CST_ELT): Redefine using vector_cst_elt.
+ (VECTOR_CST_LOG2_NPATTERNS, VECTOR_CST_NPATTERNS): New macros.
+ (VECTOR_CST_NELTS_PER_PATTERN, VECTOR_CST_DUPLICATE_P): Likewise.
+ (VECTOR_CST_STEPPED_P, VECTOR_CST_ENCODED_ELTS): Likewise.
+ (VECTOR_CST_ENCODED_ELT): Likewise.
+ (vector_cst_encoded_nelts): New function.
+ (make_vector): Take the values of VECTOR_CST_LOG2_NPATTERNS and
+ VECTOR_CST_NELTS_PER_PATTERN as arguments.
+ (vector_cst_int_elt, vector_cst_elt): Declare.
+ * tree.c: Include tree-vector-builder.h.
+ (tree_code_size): Abort if passed VECTOR_CST.
+ (tree_size): Update for new VECTOR_CST layout.
+ (make_vector): Take the values of VECTOR_CST_LOG2_NPATTERNS and
+ VECTOR_CST_NELTS_PER_PATTERN as arguments.
+ (build_vector): Use tree_vector_builder.
+ (vector_cst_int_elt, vector_cst_elt): New functions.
+ (drop_tree_overflow): For VECTOR_CST, drop the TREE_OVERFLOW from the
+ encoded elements and then create the vector in the canonical form.
+ (check_vector_cst, check_vector_cst_duplicate, check_vector_cst_fill)
+ (check_vector_cst_stepped, test_vector_cst_patterns): New functions.
+ (tree_c_tests): Call test_vector_cst_patterns.
+ * lto-streamer-out.c (DFS::DFS_write_tree_body): Handle the new
+ VECTOR_CST fields.
+ (hash_tree): Likewise.
+ * tree-streamer-out.c (write_ts_vector_tree_pointers): Likewise.
+ (streamer_write_tree_header): Likewise.
+ * tree-streamer-in.c (lto_input_ts_vector_tree_pointers): Likewise.
+ (streamer_alloc_tree): Likewise. Update call to make_vector.
+ * fold-const.c (fold_ternary_loc): Avoid using VECTOR_CST_ELTS.
+
2017-12-07 Richard Sandiford <richard.sandiford@linaro.org>
* selftest.h (ASSERT_TRUE_AT, ASSERT_FALSE_AT, ASSERT_EQ_AT)
tree-vect-loop-manip.o \
tree-vect-slp.o \
tree-vectorizer.o \
+ tree-vector-builder.o \
tree-vrp.o \
tree.o \
typed-splay-tree.o \
imaginary parts respectively.
@item VECTOR_CST
-These nodes are used to represent vector constants, whose parts are
-constant nodes. Each individual constant node is either an integer or a
-double constant node. The first operand is a @code{TREE_LIST} of the
-constant nodes and is accessed through @code{TREE_VECTOR_CST_ELTS}.
+These nodes are used to represent vector constants. Each vector
+constant @var{v} is treated as a specific instance of an arbitrary-length
+sequence that itself contains @samp{VECTOR_CST_NPATTERNS (@var{v})}
+interleaved patterns. Each pattern has the form:
+
+@smallexample
+@{ @var{base0}, @var{base1}, @var{base1} + @var{step}, @var{base1} + @var{step} * 2, @dots{} @}
+@end smallexample
+
+The first three elements in each pattern are enough to determine the
+values of the other elements. However, if all @var{step}s are zero,
+only the first two elements are needed. If in addition each @var{base1}
+is equal to the corresponding @var{base0}, only the first element in
+each pattern is needed. The number of encoded elements per pattern
+is given by @samp{VECTOR_CST_NELTS_PER_PATTERN (@var{v})}.
+
+For example, the constant:
+
+@smallexample
+@{ 0, 1, 2, 6, 3, 8, 4, 10, 5, 12, 6, 14, 7, 16, 8, 18 @}
+@end smallexample
+
+is interpreted as an interleaving of the sequences:
+
+@smallexample
+@{ 0, 2, 3, 4, 5, 6, 7, 8 @}
+@{ 1, 6, 8, 10, 12, 14, 16, 18 @}
+@end smallexample
+
+where the sequences are represented by the following patterns:
+
+@smallexample
+@var{base0} == 0, @var{base1} == 2, @var{step} == 1
+@var{base0} == 1, @var{base1} == 6, @var{step} == 2
+@end smallexample
+
+In this case:
+
+@smallexample
+VECTOR_CST_NPATTERNS (@var{v}) == 2
+VECTOR_CST_NELTS_PER_PATTERN (@var{v}) == 3
+@end smallexample
+
+The vector is therefore encoded using the first 6 elements
+(@samp{@{ 0, 1, 2, 6, 3, 8 @}}), with the remaining 10 elements
+being implicit extensions of them.
+
+Sometimes this scheme can create two possible encodings of the same
+vector. For example @{ 0, 1 @} could be seen as two patterns with
+one element each or one pattern with two elements (@var{base0} and
+@var{base1}). The canonical encoding is always the one with the
+fewest patterns or (if both encodings have the same number of
+petterns) the one with the fewest encoded elements.
+
+@samp{vector_cst_encoding_nelts (@var{v})} gives the total number of
+encoded elements in @var{v}, which is 6 in the example above.
+@code{VECTOR_CST_ENCODED_ELTS (@var{v})} gives a pointer to the elements
+encoded in @var{v} and @code{VECTOR_CST_ENCODED_ELT (@var{v}, @var{i})}
+accesses the value of encoded element @var{i}.
+
+@samp{VECTOR_CST_DUPLICATE_P (@var{v})} is true if @var{v} simply contains
+repeated instances of @samp{VECTOR_CST_NPATTERNS (@var{v})} values. This is
+a shorthand for testing @samp{VECTOR_CST_NELTS_PER_PATTERN (@var{v}) == 1}.
+
+@samp{VECTOR_CST_STEPPED_P (@var{v})} is true if at least one
+pattern in @var{v} has a nonzero step. This is a shorthand for
+testing @samp{VECTOR_CST_NELTS_PER_PATTERN (@var{v}) == 3}.
+
+The utility function @code{vector_cst_elt} gives the value of an
+arbitrary index as a @code{tree}. @code{vector_cst_int_elt} gives
+the same value as a @code{wide_int}.
@item STRING_CST
These nodes represent string-constants. The @code{TREE_STRING_LENGTH}
unsigned int nelts = VECTOR_CST_NELTS (arg0);
auto_vec<tree, 32> elts (nelts);
elts.quick_grow (nelts);
- memcpy (&elts[0], VECTOR_CST_ELTS (arg0),
- sizeof (tree) * nelts);
- elts[k] = arg1;
+ for (unsigned int i = 0; i < VECTOR_CST_NELTS (arg0); ++i)
+ elts[i] = (i == k ? arg1 : VECTOR_CST_ELT (arg0, i));
return build_vector (type, elts);
}
}
if (CODE_CONTAINS_STRUCT (code, TS_VECTOR))
{
- for (unsigned i = 0; i < VECTOR_CST_NELTS (expr); ++i)
- DFS_follow_tree_edge (VECTOR_CST_ELT (expr, i));
+ unsigned int count = vector_cst_encoded_nelts (expr);
+ for (unsigned int i = 0; i < count; ++i)
+ DFS_follow_tree_edge (VECTOR_CST_ENCODED_ELT (expr, i));
}
if (CODE_CONTAINS_STRUCT (code, TS_COMPLEX))
}
if (CODE_CONTAINS_STRUCT (code, TS_VECTOR))
- for (unsigned i = 0; i < VECTOR_CST_NELTS (t); ++i)
- visit (VECTOR_CST_ELT (t, i));
+ {
+ unsigned int count = vector_cst_encoded_nelts (t);
+ for (unsigned int i = 0; i < count; ++i)
+ visit (VECTOR_CST_ENCODED_ELT (t, i));
+ }
if (CODE_CONTAINS_STRUCT (code, TS_COMPLEX))
{
+2017-12-07 Richard Sandiford <richard.sandiford@arm.com>
+
+ * lto.c (compare_tree_sccs_1): Compare the new VECTOR_CST flags.
+
2017-12-07 Martin Sebor <msebor@redhat.com>
PR c/81544
TREE_FIXED_CST_PTR (t1), TREE_FIXED_CST_PTR (t2)))
return false;
+ if (CODE_CONTAINS_STRUCT (code, TS_VECTOR))
+ {
+ compare_values (VECTOR_CST_LOG2_NPATTERNS);
+ compare_values (VECTOR_CST_NELTS_PER_PATTERN);
+ }
+
if (CODE_CONTAINS_STRUCT (code, TS_DECL_COMMON))
{
compare_values (DECL_MODE);
if (CODE_CONTAINS_STRUCT (code, TS_VECTOR))
{
- unsigned i;
/* Note that the number of elements for EXPR has already been emitted
in EXPR's header (see streamer_write_tree_header). */
- for (i = 0; i < VECTOR_CST_NELTS (t1); ++i)
- compare_tree_edges (VECTOR_CST_ELT (t1, i), VECTOR_CST_ELT (t2, i));
+ unsigned int count = vector_cst_encoded_nelts (t1);
+ for (unsigned int i = 0; i < count; ++i)
+ compare_tree_edges (VECTOR_CST_ENCODED_ELT (t1, i),
+ VECTOR_CST_ENCODED_ELT (t2, i));
}
if (CODE_CONTAINS_STRUCT (code, TS_COMPLEX))
/* VEC length. This field is only used with TREE_VEC. */
int length;
- /* Number of elements. This field is only used with VECTOR_CST. */
- unsigned int nelts;
+ /* This field is only used with VECTOR_CST. */
+ struct {
+ /* The value of VECTOR_CST_LOG2_NPATTERNS. */
+ unsigned int log2_npatterns : 8;
+
+ /* The value of VECTOR_CST_NELTS_PER_PATTERN. */
+ unsigned int nelts_per_pattern : 8;
+
+ /* For future expansion. */
+ unsigned int unused : 16;
+ } vector_cst;
/* SSA version number. This field is only used with SSA_NAME. */
unsigned int version;
struct GTY(()) tree_vector {
struct tree_typed typed;
- tree GTY ((length ("VECTOR_CST_NELTS ((tree) &%h)"))) elts[1];
+ tree GTY ((length ("vector_cst_encoded_nelts ((tree) &%h)"))) elts[1];
};
struct GTY(()) tree_identifier {
}
else if (CODE_CONTAINS_STRUCT (code, TS_VECTOR))
{
- HOST_WIDE_INT len = streamer_read_hwi (ib);
- result = make_vector (len);
+ bitpack_d bp = streamer_read_bitpack (ib);
+ unsigned int log2_npatterns = bp_unpack_value (&bp, 8);
+ unsigned int nelts_per_pattern = bp_unpack_value (&bp, 8);
+ result = make_vector (log2_npatterns, nelts_per_pattern);
}
else if (CODE_CONTAINS_STRUCT (code, TS_BINFO))
{
lto_input_ts_vector_tree_pointers (struct lto_input_block *ib,
struct data_in *data_in, tree expr)
{
- unsigned i;
- for (i = 0; i < VECTOR_CST_NELTS (expr); ++i)
- VECTOR_CST_ELT (expr, i) = stream_read_tree (ib, data_in);
+ unsigned int count = vector_cst_encoded_nelts (expr);
+ for (unsigned int i = 0; i < count; ++i)
+ VECTOR_CST_ENCODED_ELT (expr, i) = stream_read_tree (ib, data_in);
}
static void
write_ts_vector_tree_pointers (struct output_block *ob, tree expr, bool ref_p)
{
- unsigned i;
/* Note that the number of elements for EXPR has already been emitted
in EXPR's header (see streamer_write_tree_header). */
- for (i = 0; i < VECTOR_CST_NELTS (expr); ++i)
- stream_write_tree (ob, VECTOR_CST_ELT (expr, i), ref_p);
+ unsigned int count = vector_cst_encoded_nelts (expr);
+ for (unsigned int i = 0; i < count; ++i)
+ stream_write_tree (ob, VECTOR_CST_ENCODED_ELT (expr, i), ref_p);
}
else if (CODE_CONTAINS_STRUCT (code, TS_IDENTIFIER))
write_identifier (ob, ob->main_stream, expr);
else if (CODE_CONTAINS_STRUCT (code, TS_VECTOR))
- streamer_write_hwi (ob, VECTOR_CST_NELTS (expr));
+ {
+ bitpack_d bp = bitpack_create (ob->main_stream);
+ bp_pack_value (&bp, VECTOR_CST_LOG2_NPATTERNS (expr), 8);
+ bp_pack_value (&bp, VECTOR_CST_NELTS_PER_PATTERN (expr), 8);
+ streamer_write_bitpack (&bp);
+ }
else if (CODE_CONTAINS_STRUCT (code, TS_VEC))
streamer_write_hwi (ob, TREE_VEC_LENGTH (expr));
else if (CODE_CONTAINS_STRUCT (code, TS_BINFO))
--- /dev/null
+/* A class for building vector tree constants.
+ Copyright (C) 2017 Free Software Foundation, Inc.
+
+This file is part of GCC.
+
+GCC is free software; you can redistribute it and/or modify it under
+the terms of the GNU General Public License as published by the Free
+Software Foundation; either version 3, or (at your option) any later
+version.
+
+GCC is distributed in the hope that it will be useful, but WITHOUT ANY
+WARRANTY; without even the implied warranty of MERCHANTABILITY or
+FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
+for more details.
+
+You should have received a copy of the GNU General Public License
+along with GCC; see the file COPYING3. If not see
+<http://www.gnu.org/licenses/>. */
+
+#include "config.h"
+#include "system.h"
+#include "coretypes.h"
+#include "tree.h"
+#include "fold-const.h"
+#include "tree-vector-builder.h"
+
+/* Try to start building a new vector of type TYPE that holds the result of
+ a unary operation on VECTOR_CST T. ALLOW_STEPPED_P is true if the
+ operation can handle stepped encodings directly, without having to
+ expand the full sequence.
+
+ Return true if the operation is possible, which it always is when
+ ALLOW_STEPPED_P is true. Leave the builder unchanged otherwise. */
+
+bool
+tree_vector_builder::new_unary_operation (tree type, tree t,
+ bool allow_stepped_p)
+{
+ unsigned int full_nelts = TYPE_VECTOR_SUBPARTS (type);
+ gcc_assert (full_nelts == TYPE_VECTOR_SUBPARTS (TREE_TYPE (t)));
+ unsigned int npatterns = VECTOR_CST_NPATTERNS (t);
+ unsigned int nelts_per_pattern = VECTOR_CST_NELTS_PER_PATTERN (t);
+ if (!allow_stepped_p && nelts_per_pattern > 2)
+ {
+ npatterns = full_nelts;
+ nelts_per_pattern = 1;
+ }
+ new_vector (type, npatterns, nelts_per_pattern);
+ return true;
+}
+
+/* Return a VECTOR_CST for the current constant. */
+
+tree
+tree_vector_builder::build ()
+{
+ finalize ();
+ gcc_assert (pow2p_hwi (npatterns ()));
+ tree v = make_vector (exact_log2 (npatterns ()), nelts_per_pattern ());
+ TREE_TYPE (v) = m_type;
+ memcpy (VECTOR_CST_ENCODED_ELTS (v), address (),
+ encoded_nelts () * sizeof (tree));
+ return v;
+}
--- /dev/null
+/* A class for building vector tree constants.
+ Copyright (C) 2017 Free Software Foundation, Inc.
+
+This file is part of GCC.
+
+GCC is free software; you can redistribute it and/or modify it under
+the terms of the GNU General Public License as published by the Free
+Software Foundation; either version 3, or (at your option) any later
+version.
+
+GCC is distributed in the hope that it will be useful, but WITHOUT ANY
+WARRANTY; without even the implied warranty of MERCHANTABILITY or
+FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
+for more details.
+
+You should have received a copy of the GNU General Public License
+along with GCC; see the file COPYING3. If not see
+<http://www.gnu.org/licenses/>. */
+
+#ifndef GCC_TREE_VECTOR_BUILDER_H
+#define GCC_TREE_VECTOR_BUILDER_H
+
+#include "vector-builder.h"
+
+/* This class is used to build VECTOR_CSTs from a sequence of elements.
+ See vector_builder for more details. */
+class tree_vector_builder : public vector_builder<tree, tree_vector_builder>
+{
+ typedef vector_builder<tree, tree_vector_builder> parent;
+ friend class vector_builder<tree, tree_vector_builder>;
+
+public:
+ tree_vector_builder () : m_type (0) {}
+ tree_vector_builder (tree, unsigned int, unsigned int);
+ tree build ();
+
+ tree type () const { return m_type; }
+
+ void new_vector (tree, unsigned int, unsigned int);
+ bool new_unary_operation (tree, tree, bool);
+
+private:
+ bool equal_p (const_tree, const_tree) const;
+ bool allow_steps_p () const;
+ bool integral_p (const_tree) const;
+ wide_int step (const_tree, const_tree) const;
+ bool can_elide_p (const_tree) const;
+ void note_representative (tree *, tree);
+
+ tree m_type;
+};
+
+/* Create a new builder for a vector of type TYPE. Initially encode the
+ value as NPATTERNS interleaved patterns with NELTS_PER_PATTERN elements
+ each. */
+
+inline
+tree_vector_builder::tree_vector_builder (tree type, unsigned int npatterns,
+ unsigned int nelts_per_pattern)
+{
+ new_vector (type, npatterns, nelts_per_pattern);
+}
+
+/* Start building a new vector of type TYPE. Initially encode the value
+ as NPATTERNS interleaved patterns with NELTS_PER_PATTERN elements each. */
+
+inline void
+tree_vector_builder::new_vector (tree type, unsigned int npatterns,
+ unsigned int nelts_per_pattern)
+{
+ m_type = type;
+ parent::new_vector (TYPE_VECTOR_SUBPARTS (type), npatterns,
+ nelts_per_pattern);
+}
+
+/* Return true if elements I1 and I2 are equal. */
+
+inline bool
+tree_vector_builder::equal_p (const_tree elt1, const_tree elt2) const
+{
+ return operand_equal_p (elt1, elt2, 0);
+}
+
+/* Return true if a stepped representation is OK. We don't allow
+ linear series for anything other than integers, to avoid problems
+ with rounding. */
+
+inline bool
+tree_vector_builder::allow_steps_p () const
+{
+ return INTEGRAL_TYPE_P (TREE_TYPE (m_type));
+}
+
+/* Return true if ELT can be interpreted as an integer. */
+
+inline bool
+tree_vector_builder::integral_p (const_tree elt) const
+{
+ return TREE_CODE (elt) == INTEGER_CST;
+}
+
+/* Return the value of element ELT2 minus the value of element ELT1.
+ Both elements are known to be INTEGER_CSTs. */
+
+inline wide_int
+tree_vector_builder::step (const_tree elt1, const_tree elt2) const
+{
+ return wi::to_wide (elt2) - wi::to_wide (elt1);
+}
+
+/* Return true if we can drop element ELT, even if the retained elements
+ are different. Return false if this would mean losing overflow
+ information. */
+
+inline bool
+tree_vector_builder::can_elide_p (const_tree elt) const
+{
+ return !CONSTANT_CLASS_P (elt) || !TREE_OVERFLOW (elt);
+}
+
+/* Record that ELT2 is being elided, given that ELT1_PTR points to the last
+ encoded element for the containing pattern. */
+
+inline void
+tree_vector_builder::note_representative (tree *elt1_ptr, tree elt2)
+{
+ if (CONSTANT_CLASS_P (elt2) && TREE_OVERFLOW (elt2))
+ {
+ gcc_assert (operand_equal_p (*elt1_ptr, elt2, 0));
+ if (!TREE_OVERFLOW (elt2))
+ *elt1_ptr = elt2;
+ }
+}
+
+#endif
#include "attribs.h"
#include "rtl.h"
#include "regs.h"
+#include "tree-vector-builder.h"
/* Tree code classes. */
case REAL_CST: return sizeof (tree_real_cst);
case FIXED_CST: return sizeof (tree_fixed_cst);
case COMPLEX_CST: return sizeof (tree_complex);
- case VECTOR_CST: return sizeof (tree_vector);
+ case VECTOR_CST: gcc_unreachable ();
case STRING_CST: gcc_unreachable ();
default:
gcc_checking_assert (code >= NUM_TREE_CODES);
case VECTOR_CST:
return (sizeof (struct tree_vector)
- + (VECTOR_CST_NELTS (node) - 1) * sizeof (tree));
+ + (vector_cst_encoded_nelts (node) - 1) * sizeof (tree));
case STRING_CST:
return TREE_STRING_LENGTH (node) + offsetof (struct tree_string, str) + 1;
&& (tree_fits_shwi_p (x) || tree_fits_uhwi_p (x)));
}
-/* Build a newly constructed VECTOR_CST node of length LEN. */
+/* Build a newly constructed VECTOR_CST with the given values of
+ (VECTOR_CST_)LOG2_NPATTERNS and (VECTOR_CST_)NELTS_PER_PATTERN. */
tree
-make_vector (unsigned len MEM_STAT_DECL)
+make_vector (unsigned log2_npatterns,
+ unsigned int nelts_per_pattern MEM_STAT_DECL)
{
+ gcc_assert (IN_RANGE (nelts_per_pattern, 1, 3));
tree t;
- unsigned length = (len - 1) * sizeof (tree) + sizeof (struct tree_vector);
+ unsigned npatterns = 1 << log2_npatterns;
+ unsigned encoded_nelts = npatterns * nelts_per_pattern;
+ unsigned length = (sizeof (struct tree_vector)
+ + (encoded_nelts - 1) * sizeof (tree));
record_node_allocation_statistics (VECTOR_CST, length);
TREE_SET_CODE (t, VECTOR_CST);
TREE_CONSTANT (t) = 1;
- VECTOR_CST_NELTS (t) = len;
+ VECTOR_CST_LOG2_NPATTERNS (t) = log2_npatterns;
+ VECTOR_CST_NELTS_PER_PATTERN (t) = nelts_per_pattern;
return t;
}
tree
build_vector (tree type, vec<tree> vals MEM_STAT_DECL)
{
- unsigned int nelts = vals.length ();
- gcc_assert (nelts == TYPE_VECTOR_SUBPARTS (type));
- int over = 0;
- unsigned cnt = 0;
- tree v = make_vector (nelts);
- TREE_TYPE (v) = type;
-
- /* Iterate through elements and check for overflow. */
- for (cnt = 0; cnt < nelts; ++cnt)
- {
- tree value = vals[cnt];
-
- VECTOR_CST_ELT (v, cnt) = value;
-
- /* Don't crash if we get an address constant. */
- if (!CONSTANT_CLASS_P (value))
- continue;
-
- over |= TREE_OVERFLOW (value);
- }
-
- TREE_OVERFLOW (v) = over;
- return v;
+ gcc_assert (vals.length () == TYPE_VECTOR_SUBPARTS (type));
+ tree_vector_builder builder (type, vals.length (), 1);
+ builder.splice (vals);
+ return builder.build ();
}
/* Return a new VECTOR_CST node whose type is TYPE and whose values
return cand;
}
+/* Return the value of element I of VECTOR_CST T as a wide_int. */
+
+wide_int
+vector_cst_int_elt (const_tree t, unsigned int i)
+{
+ /* First handle elements that are directly encoded. */
+ unsigned int encoded_nelts = vector_cst_encoded_nelts (t);
+ if (i < encoded_nelts)
+ return wi::to_wide (VECTOR_CST_ENCODED_ELT (t, i));
+
+ /* Identify the pattern that contains element I and work out the index of
+ the last encoded element for that pattern. */
+ unsigned int npatterns = VECTOR_CST_NPATTERNS (t);
+ unsigned int pattern = i % npatterns;
+ unsigned int count = i / npatterns;
+ unsigned int final_i = encoded_nelts - npatterns + pattern;
+
+ /* If there are no steps, the final encoded value is the right one. */
+ if (!VECTOR_CST_STEPPED_P (t))
+ return wi::to_wide (VECTOR_CST_ENCODED_ELT (t, final_i));
+
+ /* Otherwise work out the value from the last two encoded elements. */
+ tree v1 = VECTOR_CST_ENCODED_ELT (t, final_i - npatterns);
+ tree v2 = VECTOR_CST_ENCODED_ELT (t, final_i);
+ wide_int diff = wi::to_wide (v2) - wi::to_wide (v1);
+ return wi::to_wide (v2) + (count - 2) * diff;
+}
+
+/* Return the value of element I of VECTOR_CST T. */
+
+tree
+vector_cst_elt (const_tree t, unsigned int i)
+{
+ /* First handle elements that are directly encoded. */
+ unsigned int encoded_nelts = vector_cst_encoded_nelts (t);
+ if (i < encoded_nelts)
+ return VECTOR_CST_ENCODED_ELT (t, i);
+
+ /* If there are no steps, the final encoded value is the right one. */
+ if (!VECTOR_CST_STEPPED_P (t))
+ {
+ /* Identify the pattern that contains element I and work out the index of
+ the last encoded element for that pattern. */
+ unsigned int npatterns = VECTOR_CST_NPATTERNS (t);
+ unsigned int pattern = i % npatterns;
+ unsigned int final_i = encoded_nelts - npatterns + pattern;
+ return VECTOR_CST_ENCODED_ELT (t, final_i);
+ }
+
+ /* Otherwise work out the value from the last two encoded elements. */
+ return wide_int_to_tree (TREE_TYPE (TREE_TYPE (t)),
+ vector_cst_int_elt (t, i));
+}
/* Given an initializer INIT, return TRUE if INIT is zero or some
aggregate of zeros. Otherwise return FALSE. */
if (TREE_CODE (t) == INTEGER_CST)
return wide_int_to_tree (TREE_TYPE (t), wi::to_wide (t));
+ /* For VECTOR_CST, remove the overflow bits from the encoded elements
+ and canonicalize the result. */
+ if (TREE_CODE (t) == VECTOR_CST)
+ {
+ tree_vector_builder builder;
+ builder.new_unary_operation (TREE_TYPE (t), t, true);
+ unsigned int count = builder.encoded_nelts ();
+ for (unsigned int i = 0; i < count; ++i)
+ {
+ tree elt = VECTOR_CST_ELT (t, i);
+ if (TREE_OVERFLOW (elt))
+ elt = drop_tree_overflow (elt);
+ builder.quick_push (elt);
+ }
+ return builder.build ();
+ }
+
/* Otherwise, as all tcc_constants are possibly shared, copy the node
and drop the flag. */
t = copy_node (t);
if (TREE_OVERFLOW (TREE_IMAGPART (t)))
TREE_IMAGPART (t) = drop_tree_overflow (TREE_IMAGPART (t));
}
- if (TREE_CODE (t) == VECTOR_CST)
- {
- for (unsigned i = 0; i < VECTOR_CST_NELTS (t); ++i)
- {
- tree& elt = VECTOR_CST_ELT (t, i);
- if (TREE_OVERFLOW (elt))
- elt = drop_tree_overflow (elt);
- }
- }
+
return t;
}
ASSERT_FALSE (FORCED_LABEL (label_decl));
}
+/* Check that VECTOR_CST ACTUAL contains the elements in EXPECTED. */
+
+static void
+check_vector_cst (vec<tree> expected, tree actual)
+{
+ ASSERT_EQ (expected.length (), TYPE_VECTOR_SUBPARTS (TREE_TYPE (actual)));
+ for (unsigned int i = 0; i < expected.length (); ++i)
+ ASSERT_EQ (wi::to_wide (expected[i]),
+ wi::to_wide (vector_cst_elt (actual, i)));
+}
+
+/* Check that VECTOR_CST ACTUAL contains NPATTERNS duplicated elements,
+ and that its elements match EXPECTED. */
+
+static void
+check_vector_cst_duplicate (vec<tree> expected, tree actual,
+ unsigned int npatterns)
+{
+ ASSERT_EQ (npatterns, VECTOR_CST_NPATTERNS (actual));
+ ASSERT_EQ (1, VECTOR_CST_NELTS_PER_PATTERN (actual));
+ ASSERT_EQ (npatterns, vector_cst_encoded_nelts (actual));
+ ASSERT_TRUE (VECTOR_CST_DUPLICATE_P (actual));
+ ASSERT_FALSE (VECTOR_CST_STEPPED_P (actual));
+ check_vector_cst (expected, actual);
+}
+
+/* Check that VECTOR_CST ACTUAL contains NPATTERNS foreground elements
+ and NPATTERNS background elements, and that its elements match
+ EXPECTED. */
+
+static void
+check_vector_cst_fill (vec<tree> expected, tree actual,
+ unsigned int npatterns)
+{
+ ASSERT_EQ (npatterns, VECTOR_CST_NPATTERNS (actual));
+ ASSERT_EQ (2, VECTOR_CST_NELTS_PER_PATTERN (actual));
+ ASSERT_EQ (2 * npatterns, vector_cst_encoded_nelts (actual));
+ ASSERT_FALSE (VECTOR_CST_DUPLICATE_P (actual));
+ ASSERT_FALSE (VECTOR_CST_STEPPED_P (actual));
+ check_vector_cst (expected, actual);
+}
+
+/* Check that VECTOR_CST ACTUAL contains NPATTERNS stepped patterns,
+ and that its elements match EXPECTED. */
+
+static void
+check_vector_cst_stepped (vec<tree> expected, tree actual,
+ unsigned int npatterns)
+{
+ ASSERT_EQ (npatterns, VECTOR_CST_NPATTERNS (actual));
+ ASSERT_EQ (3, VECTOR_CST_NELTS_PER_PATTERN (actual));
+ ASSERT_EQ (3 * npatterns, vector_cst_encoded_nelts (actual));
+ ASSERT_FALSE (VECTOR_CST_DUPLICATE_P (actual));
+ ASSERT_TRUE (VECTOR_CST_STEPPED_P (actual));
+ check_vector_cst (expected, actual);
+}
+
+/* Test the creation of VECTOR_CSTs. */
+
+static void
+test_vector_cst_patterns ()
+{
+ auto_vec<tree, 8> elements (8);
+ elements.quick_grow (8);
+ tree element_type = build_nonstandard_integer_type (16, true);
+ tree vector_type = build_vector_type (element_type, 8);
+
+ /* Test a simple linear series with a base of 0 and a step of 1:
+ { 0, 1, 2, 3, 4, 5, 6, 7 }. */
+ for (unsigned int i = 0; i < 8; ++i)
+ elements[i] = build_int_cst (element_type, i);
+ check_vector_cst_stepped (elements, build_vector (vector_type, elements), 1);
+
+ /* Try the same with the first element replaced by 100:
+ { 100, 1, 2, 3, 4, 5, 6, 7 }. */
+ elements[0] = build_int_cst (element_type, 100);
+ check_vector_cst_stepped (elements, build_vector (vector_type, elements), 1);
+
+ /* Try a series that wraps around.
+ { 100, 65531, 65532, 65533, 65534, 65535, 0, 1 }. */
+ for (unsigned int i = 1; i < 8; ++i)
+ elements[i] = build_int_cst (element_type, (65530 + i) & 0xffff);
+ check_vector_cst_stepped (elements, build_vector (vector_type, elements), 1);
+
+ /* Try a downward series:
+ { 100, 79, 78, 77, 76, 75, 75, 73 }. */
+ for (unsigned int i = 1; i < 8; ++i)
+ elements[i] = build_int_cst (element_type, 80 - i);
+ check_vector_cst_stepped (elements, build_vector (vector_type, elements), 1);
+
+ /* Try two interleaved series with different bases and steps:
+ { 100, 53, 66, 206, 62, 212, 58, 218 }. */
+ elements[1] = build_int_cst (element_type, 53);
+ for (unsigned int i = 2; i < 8; i += 2)
+ {
+ elements[i] = build_int_cst (element_type, 70 - i * 2);
+ elements[i + 1] = build_int_cst (element_type, 200 + i * 3);
+ }
+ check_vector_cst_stepped (elements, build_vector (vector_type, elements), 2);
+
+ /* Try a duplicated value:
+ { 100, 100, 100, 100, 100, 100, 100, 100 }. */
+ for (unsigned int i = 1; i < 8; ++i)
+ elements[i] = elements[0];
+ check_vector_cst_duplicate (elements,
+ build_vector (vector_type, elements), 1);
+
+ /* Try an interleaved duplicated value:
+ { 100, 55, 100, 55, 100, 55, 100, 55 }. */
+ elements[1] = build_int_cst (element_type, 55);
+ for (unsigned int i = 2; i < 8; ++i)
+ elements[i] = elements[i - 2];
+ check_vector_cst_duplicate (elements,
+ build_vector (vector_type, elements), 2);
+
+ /* Try a duplicated value with 2 exceptions
+ { 41, 97, 100, 55, 100, 55, 100, 55 }. */
+ elements[0] = build_int_cst (element_type, 41);
+ elements[1] = build_int_cst (element_type, 97);
+ check_vector_cst_fill (elements, build_vector (vector_type, elements), 2);
+
+ /* Try with and without a step
+ { 41, 97, 100, 21, 100, 35, 100, 49 }. */
+ for (unsigned int i = 3; i < 8; i += 2)
+ elements[i] = build_int_cst (element_type, i * 7);
+ check_vector_cst_stepped (elements, build_vector (vector_type, elements), 2);
+
+ /* Try a fully-general constant:
+ { 41, 97, 100, 21, 100, 9990, 100, 49 }. */
+ elements[5] = build_int_cst (element_type, 9990);
+ check_vector_cst_fill (elements, build_vector (vector_type, elements), 4);
+}
+
/* Run all of the selftests within this file. */
void
test_integer_constants ();
test_identifiers ();
test_labels ();
+ test_vector_cst_patterns ();
}
} // namespace selftest
whose contents are other constant nodes. */
DEFTREECODE (COMPLEX_CST, "complex_cst", tcc_constant, 0)
-/* Contents are in VECTOR_CST_ELTS field. */
+/* See generic.texi for details. */
DEFTREECODE (VECTOR_CST, "vector_cst", tcc_constant, 0)
/* Contents are TREE_STRING_LENGTH and the actual contents of the string. */
#define TREE_REALPART(NODE) (COMPLEX_CST_CHECK (NODE)->complex.real)
#define TREE_IMAGPART(NODE) (COMPLEX_CST_CHECK (NODE)->complex.imag)
-/* In a VECTOR_CST node. */
-#define VECTOR_CST_NELTS(NODE) (VECTOR_CST_CHECK (NODE)->base.u.nelts)
-#define VECTOR_CST_ELTS(NODE) (VECTOR_CST_CHECK (NODE)->vector.elts)
-#define VECTOR_CST_ELT(NODE,IDX) (VECTOR_CST_CHECK (NODE)->vector.elts[IDX])
+/* In a VECTOR_CST node. See generic.texi for details. */
+#define VECTOR_CST_NELTS(NODE) (TYPE_VECTOR_SUBPARTS (TREE_TYPE (NODE)))
+#define VECTOR_CST_ELT(NODE,IDX) vector_cst_elt (NODE, IDX)
+
+#define VECTOR_CST_LOG2_NPATTERNS(NODE) \
+ (VECTOR_CST_CHECK (NODE)->base.u.vector_cst.log2_npatterns)
+#define VECTOR_CST_NPATTERNS(NODE) \
+ (1U << VECTOR_CST_LOG2_NPATTERNS (NODE))
+#define VECTOR_CST_NELTS_PER_PATTERN(NODE) \
+ (VECTOR_CST_CHECK (NODE)->base.u.vector_cst.nelts_per_pattern)
+#define VECTOR_CST_DUPLICATE_P(NODE) \
+ (VECTOR_CST_NELTS_PER_PATTERN (NODE) == 1)
+#define VECTOR_CST_STEPPED_P(NODE) \
+ (VECTOR_CST_NELTS_PER_PATTERN (NODE) == 3)
+#define VECTOR_CST_ENCODED_ELTS(NODE) \
+ (VECTOR_CST_CHECK (NODE)->vector.elts)
+#define VECTOR_CST_ENCODED_ELT(NODE, ELT) \
+ (VECTOR_CST_CHECK (NODE)->vector.elts[ELT])
/* Define fields and accessors for some special-purpose tree nodes. */
((NODE) == error_mark_node \
|| ((NODE) && TREE_TYPE ((NODE)) == error_mark_node))
+/* Return the number of elements encoded directly in a VECTOR_CST. */
+
+inline unsigned int
+vector_cst_encoded_nelts (const_tree t)
+{
+ return VECTOR_CST_NPATTERNS (t) * VECTOR_CST_NELTS_PER_PATTERN (t);
+}
+
extern tree decl_assembler_name (tree);
extern void overwrite_decl_assembler_name (tree decl, tree name);
extern tree decl_comdat_group (const_tree);
extern tree build_int_cst (tree, HOST_WIDE_INT);
extern tree build_int_cstu (tree type, unsigned HOST_WIDE_INT cst);
extern tree build_int_cst_type (tree, HOST_WIDE_INT);
-extern tree make_vector (unsigned CXX_MEM_STAT_INFO);
+extern tree make_vector (unsigned, unsigned CXX_MEM_STAT_INFO);
extern tree build_vector (tree, vec<tree> CXX_MEM_STAT_INFO);
extern tree build_vector_from_ctor (tree, vec<constructor_elt, va_gc> *);
extern tree build_vector_from_val (tree, tree);
extern bool initializer_zerop (const_tree);
+extern wide_int vector_cst_int_elt (const_tree, unsigned int);
+extern tree vector_cst_elt (const_tree, unsigned int);
+
/* Given a vector VEC, return its first element if all elements are
the same. Otherwise return NULL_TREE. */
--- /dev/null
+/* A class for building vector constant patterns.
+ Copyright (C) 2017 Free Software Foundation, Inc.
+
+This file is part of GCC.
+
+GCC is free software; you can redistribute it and/or modify it under
+the terms of the GNU General Public License as published by the Free
+Software Foundation; either version 3, or (at your option) any later
+version.
+
+GCC is distributed in the hope that it will be useful, but WITHOUT ANY
+WARRANTY; without even the implied warranty of MERCHANTABILITY or
+FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
+for more details.
+
+You should have received a copy of the GNU General Public License
+along with GCC; see the file COPYING3. If not see
+<http://www.gnu.org/licenses/>. */
+
+#ifndef GCC_VECTOR_BUILDER_H
+#define GCC_VECTOR_BUILDER_H
+
+/* This class is a wrapper around auto_vec<T> for building vectors of T.
+ It aims to encode each vector as npatterns interleaved patterns,
+ where each pattern represents a sequence:
+
+ { BASE0, BASE1, BASE1 + STEP, BASE1 + STEP*2, BASE1 + STEP*3, ... }
+
+ The first three elements in each pattern provide enough information
+ to derive the other elements. If all patterns have a STEP of zero,
+ we only need to encode the first two elements in each pattern.
+ If BASE1 is also equal to BASE0 for all patterns, we only need to
+ encode the first element in each pattern. The number of encoded
+ elements per pattern is given by nelts_per_pattern.
+
+ The class can be used in two ways:
+
+ 1. It can be used to build a full image of the vector, which is then
+ canonicalized by finalize (). In this case npatterns is initially
+ the number of elements in the vector and nelts_per_pattern is
+ initially 1.
+
+ 2. It can be used to build a vector that already has a known encoding.
+ This is preferred since it is more efficient and copes with
+ variable-length vectors. finalize () then canonicalizes the encoding
+ to a simpler form if possible.
+
+ The derived class Derived provides this functionality for specific Ts.
+ Derived needs to provide the following interface:
+
+ bool equal_p (T elt1, T elt2) const;
+
+ Return true if elements ELT1 and ELT2 are equal.
+
+ bool allow_steps_p () const;
+
+ Return true if a stepped representation is OK. We don't allow
+ linear series for anything other than integers, to avoid problems
+ with rounding.
+
+ bool integral_p (T elt) const;
+
+ Return true if element ELT can be interpreted as an integer.
+
+ StepType step (T elt1, T elt2) const;
+
+ Return the value of element ELT2 minus the value of element ELT1,
+ given integral_p (ELT1) && integral_p (ELT2). There is no fixed
+ choice of StepType.
+
+ bool can_elide_p (T elt) const;
+
+ Return true if we can drop element ELT, even if the retained
+ elements are different. This is provided for TREE_OVERFLOW
+ handling.
+
+ void note_representative (T *elt1_ptr, T elt2);
+
+ Record that ELT2 is being elided, given that ELT1_PTR points to
+ the last encoded element for the containing pattern. This is
+ again provided for TREE_OVERFLOW handling. */
+
+template<typename T, typename Derived>
+class vector_builder : public auto_vec<T, 32>
+{
+public:
+ vector_builder ();
+
+ unsigned int full_nelts () const { return m_full_nelts; }
+ unsigned int npatterns () const { return m_npatterns; }
+ unsigned int nelts_per_pattern () const { return m_nelts_per_pattern; }
+ unsigned int encoded_nelts () const;
+ bool encoded_full_vector_p () const;
+
+ void finalize ();
+
+protected:
+ void new_vector (unsigned int, unsigned int, unsigned int);
+ void reshape (unsigned int, unsigned int);
+ bool repeating_sequence_p (unsigned int, unsigned int, unsigned int);
+ bool stepped_sequence_p (unsigned int, unsigned int, unsigned int);
+ bool try_npatterns (unsigned int);
+
+private:
+ vector_builder (const vector_builder &);
+ vector_builder &operator= (const vector_builder &);
+ Derived *derived () { return static_cast<Derived *> (this); }
+ const Derived *derived () const;
+
+ unsigned int m_full_nelts;
+ unsigned int m_npatterns;
+ unsigned int m_nelts_per_pattern;
+};
+
+template<typename T, typename Derived>
+inline const Derived *
+vector_builder<T, Derived>::derived () const
+{
+ return static_cast<const Derived *> (this);
+}
+
+template<typename T, typename Derived>
+inline
+vector_builder<T, Derived>::vector_builder ()
+ : m_full_nelts (0),
+ m_npatterns (0),
+ m_nelts_per_pattern (0)
+{}
+
+/* Return the number of elements that are explicitly encoded. The vec
+ starts with these explicitly-encoded elements and may contain additional
+ elided elements. */
+
+template<typename T, typename Derived>
+inline unsigned int
+vector_builder<T, Derived>::encoded_nelts () const
+{
+ return m_npatterns * m_nelts_per_pattern;
+}
+
+/* Return true if every element of the vector is explicitly encoded. */
+
+template<typename T, typename Derived>
+inline bool
+vector_builder<T, Derived>::encoded_full_vector_p () const
+{
+ return m_npatterns * m_nelts_per_pattern == m_full_nelts;
+}
+
+/* Start building a vector that has FULL_NELTS elements. Initially
+ encode it using NPATTERNS patterns with NELTS_PER_PATTERN each. */
+
+template<typename T, typename Derived>
+void
+vector_builder<T, Derived>::new_vector (unsigned int full_nelts,
+ unsigned int npatterns,
+ unsigned int nelts_per_pattern)
+{
+ m_full_nelts = full_nelts;
+ m_npatterns = npatterns;
+ m_nelts_per_pattern = nelts_per_pattern;
+ this->reserve (encoded_nelts ());
+ this->truncate (0);
+}
+
+/* Change the encoding to NPATTERNS patterns of NELTS_PER_PATTERN each,
+ but without changing the underlying vector. */
+
+template<typename T, typename Derived>
+void
+vector_builder<T, Derived>::reshape (unsigned int npatterns,
+ unsigned int nelts_per_pattern)
+{
+ unsigned int old_encoded_nelts = encoded_nelts ();
+ unsigned int new_encoded_nelts = npatterns * nelts_per_pattern;
+ gcc_checking_assert (new_encoded_nelts <= old_encoded_nelts);
+ unsigned int next = new_encoded_nelts - npatterns;
+ for (unsigned int i = new_encoded_nelts; i < old_encoded_nelts; ++i)
+ {
+ derived ()->note_representative (&(*this)[next], (*this)[i]);
+ next += 1;
+ if (next == new_encoded_nelts)
+ next -= npatterns;
+ }
+ m_npatterns = npatterns;
+ m_nelts_per_pattern = nelts_per_pattern;
+}
+
+/* Return true if elements [START, END) contain a repeating sequence of
+ STEP elements. */
+
+template<typename T, typename Derived>
+bool
+vector_builder<T, Derived>::repeating_sequence_p (unsigned int start,
+ unsigned int end,
+ unsigned int step)
+{
+ for (unsigned int i = start; i < end - step; ++i)
+ if (!derived ()->equal_p ((*this)[i], (*this)[i + step]))
+ return false;
+ return true;
+}
+
+/* Return true if elements [START, END) contain STEP interleaved linear
+ series. */
+
+template<typename T, typename Derived>
+bool
+vector_builder<T, Derived>::stepped_sequence_p (unsigned int start,
+ unsigned int end,
+ unsigned int step)
+{
+ if (!derived ()->allow_steps_p ())
+ return false;
+
+ for (unsigned int i = start + step * 2; i < end; ++i)
+ {
+ T elt1 = (*this)[i - step * 2];
+ T elt2 = (*this)[i - step];
+ T elt3 = (*this)[i];
+
+ if (!derived ()->integral_p (elt1)
+ || !derived ()->integral_p (elt2)
+ || !derived ()->integral_p (elt3))
+ return false;
+
+ if (derived ()->step (elt1, elt2) != derived ()->step (elt2, elt3))
+ return false;
+
+ if (!derived ()->can_elide_p (elt3))
+ return false;
+ }
+ return true;
+}
+
+/* Try to change the number of encoded patterns to NPATTERNS, returning
+ true on success. */
+
+template<typename T, typename Derived>
+bool
+vector_builder<T, Derived>::try_npatterns (unsigned int npatterns)
+{
+ if (m_nelts_per_pattern == 1)
+ {
+ /* See whether NPATTERNS is valid with the current 1-element-per-pattern
+ encoding. */
+ if (repeating_sequence_p (0, encoded_nelts (), npatterns))
+ {
+ reshape (npatterns, 1);
+ return true;
+ }
+
+ /* We can only increase the number of elements per pattern if all
+ elements are still encoded explicitly. */
+ if (!encoded_full_vector_p ())
+ return false;
+ }
+
+ if (m_nelts_per_pattern <= 2)
+ {
+ /* See whether NPATTERNS is valid with a 2-element-per-pattern
+ encoding. */
+ if (repeating_sequence_p (npatterns, encoded_nelts (), npatterns))
+ {
+ reshape (npatterns, 2);
+ return true;
+ }
+
+ /* We can only increase the number of elements per pattern if all
+ elements are still encoded explicitly. */
+ if (!encoded_full_vector_p ())
+ return false;
+ }
+
+ if (m_nelts_per_pattern <= 3)
+ {
+ /* See whether we have NPATTERNS interleaved linear series,
+ giving a 3-element-per-pattern encoding. */
+ if (stepped_sequence_p (npatterns, encoded_nelts (), npatterns))
+ {
+ reshape (npatterns, 3);
+ return true;
+ }
+ return false;
+ }
+
+ gcc_unreachable ();
+}
+
+/* Replace the current encoding with the canonical form. */
+
+template<typename T, typename Derived>
+void
+vector_builder<T, Derived>::finalize ()
+{
+ /* The encoding requires the same number of elements to come from each
+ pattern. */
+ gcc_assert (m_full_nelts % m_npatterns == 0);
+
+ /* Allow the caller to build more elements than necessary. For example,
+ it's often convenient to build a stepped vector from the natural
+ encoding of three elements even if the vector itself only has two. */
+ if (m_full_nelts <= encoded_nelts ())
+ {
+ m_npatterns = m_full_nelts;
+ m_nelts_per_pattern = 1;
+ }
+
+ /* Try to whittle down the number of elements per pattern. That is:
+
+ 1. If we have stepped patterns whose steps are all 0, reduce the
+ number of elements per pattern from 3 to 2.
+
+ 2. If we have background fill values that are the same as the
+ foreground values, reduce the number of elements per pattern
+ from 2 to 1. */
+ while (m_nelts_per_pattern > 1
+ && repeating_sequence_p (encoded_nelts () - m_npatterns * 2,
+ encoded_nelts (), m_npatterns))
+ /* The last two sequences of M_NPATTERNS elements are equal,
+ so remove the last one. */
+ reshape (m_npatterns, m_nelts_per_pattern - 1);
+
+ if (pow2p_hwi (m_npatterns))
+ {
+ /* Try to halve the number of patterns while doing so gives a
+ valid pattern. This approach is linear in the number of
+ elements, whereas searcing from 1 up would be O(n*log(n)).
+
+ Each halving step tries to keep the number of elements per pattern
+ the same. If that isn't possible, and if all elements are still
+ explicitly encoded, the halving step can instead increase the number
+ of elements per pattern.
+
+ E.g. for:
+
+ { 0, 2, 3, 4, 5, 6, 7, 8 } npatterns == 8 full_nelts == 8
+
+ we first realize that the second half of the sequence is not
+ equal to the first, so we cannot maintain 1 element per pattern
+ for npatterns == 4. Instead we halve the number of patterns
+ and double the number of elements per pattern, treating this
+ as a "foreground" { 0, 2, 3, 4 } against a "background" of
+ { 5, 6, 7, 8 | 5, 6, 7, 8 ... }:
+
+ { 0, 2, 3, 4 | 5, 6, 7, 8 } npatterns == 4
+
+ Next we realize that this is *not* a foreround of { 0, 2 }
+ against a background of { 3, 4 | 3, 4 ... }, so the only
+ remaining option for reducing the number of patterns is
+ to use a foreground of { 0, 2 } against a stepped background
+ of { 1, 2 | 3, 4 | 5, 6 ... }. This is valid because we still
+ haven't elided any elements:
+
+ { 0, 2 | 3, 4 | 5, 6 } npatterns == 2
+
+ This in turn can be reduced to a foreground of { 0 } against a
+ stepped background of { 1 | 2 | 3 ... }:
+
+ { 0 | 2 | 3 } npatterns == 1
+
+ This last step would not have been possible for:
+
+ { 0, 0 | 3, 4 | 5, 6 } npatterns == 2. */
+ while ((m_npatterns & 1) == 0 && try_npatterns (m_npatterns / 2))
+ continue;
+
+ /* Builders of arbitrary fixed-length vectors can use:
+
+ new_vector (x, x, 1)
+
+ so that every element is specified explicitly. Handle cases
+ that are actually wrapping series, like { 0, 1, 2, 3, 0, 1, 2, 3 }
+ would be for 2-bit elements. We'll have treated them as
+ duplicates in the loop above. */
+ if (m_nelts_per_pattern == 1
+ && this->length () >= m_full_nelts
+ && (m_npatterns & 3) == 0
+ && stepped_sequence_p (m_npatterns / 4, m_full_nelts,
+ m_npatterns / 4))
+ {
+ reshape (m_npatterns / 4, 3);
+ while ((m_npatterns & 1) == 0 && try_npatterns (m_npatterns / 2))
+ continue;
+ }
+ }
+ else
+ /* For the non-power-of-2 case, do a simple search up from 1. */
+ for (unsigned int i = 1; i <= m_npatterns / 2; ++i)
+ if (m_npatterns % i == 0 && try_npatterns (i))
+ break;
+}
+
+#endif
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