New VECTOR_CST layout

This patch uses a simple compression scheme to represent the contents
of a VECTOR_CST using its leading elements.  There are three formats:

1) a repeating sequence of N values.  This is encoded using the first
   N elements.

2) a "foreground" sequence of N values inserted at the beginning of
   a "background" repeating sequence of N values, such as:
   { 1, 2, 0, 0, 0, 0, ... }.  This is encoded using the first 2*N
   elements.

2) a "foreground" sequence of N values inserted at the beginning of
   a "background" repeating sequence of N interleaved linear series,
   such as: { 0, 0, 8, 10, 9, 11, 10, 12, ... }.  This is encoded
   using the first 3*N elements.  In practice the foreground values
   are often part of the same series as the background values,
   such as: { 1, 11, 2, 12, 3, 13, ... }.

This reduces the amount of work involved in processing simple
vector constants and means that the encoding extends naturally
to variable-length vectors.

2017-12-07  Richard Sandiford  <richard.sandiford@arm.com>

gcc/
	* 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.

gcc/lto/
	* lto.c (compare_tree_sccs_1): Compare the new VECTOR_CST flags.

From-SVN: r255474

1 files changed, 7 insertions, 5 deletions

diff --git a/gcc/tree-streamer-in.c b/gcc/tree-streamer-in.c
index 36402c6a39c..09201393cd3 100644
--- a/gcc/tree-streamer-in.c
+++ b/gcc/tree-streamer-in.c
@@ -592,8 +592,10 @@ streamer_alloc_tree (struct lto_input_block *ib, struct data_in *data_in,
     }
   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))
     {
@@ -650,9 +652,9 @@ static void
 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);
 }