tree-dfa.c (get_ref_base_and_extent): Use range-info to refine results when processing array refs with variable index.

2018-05-18  Richard Biener  <rguenther@suse.de>

	* tree-dfa.c (get_ref_base_and_extent): Use range-info to refine
	results when processing array refs with variable index.

	* gcc.dg/tree-ssa/ssa-dse-35.c: New testcase.
	* gcc.dg/graphite/scop-10.c: Adjust to avoid dead code.
	* gcc.dg/graphite/scop-6.c: Likewise.
	* gcc.dg/graphite/scop-7.c: Likewise.
	* gcc.dg/graphite/scop-8.c: Likewise.
	* gcc.dg/graphite/scop-9.c: Likewise.

From-SVN: r260354

1 files changed, 43 insertions, 0 deletions

diff --git a/gcc/tree-dfa.c b/gcc/tree-dfa.c
index a121b880bb0..00aa75f47ab 100644
--- a/gcc/tree-dfa.c
+++ b/gcc/tree-dfa.c
@@ -529,6 +529,49 @@ get_ref_base_and_extent (tree exp, poly_int64_pod *poffset,
 		/* Remember that we have seen an array ref with a variable
 		   index.  */
 		seen_variable_array_ref = true;
+
+		wide_int min, max;
+		if (TREE_CODE (index) == SSA_NAME
+		    && (low_bound = array_ref_low_bound (exp),
+			poly_int_tree_p (low_bound))
+		    && (unit_size = array_ref_element_size (exp),
+			TREE_CODE (unit_size) == INTEGER_CST)
+		    && get_range_info (index, &min, &max) == VR_RANGE)
+		  {
+		    poly_offset_int lbound = wi::to_poly_offset (low_bound);
+		    /* Try to constrain maxsize with range information.  */
+		    offset_int omax
+		      = offset_int::from (max, TYPE_SIGN (TREE_TYPE (index)));
+		    if (known_lt (lbound, omax))
+		      {
+			poly_offset_int rmaxsize;
+			rmaxsize = (omax - lbound + 1)
+			    * wi::to_offset (unit_size) << LOG2_BITS_PER_UNIT;
+			if (!known_size_p (maxsize)
+			    || known_lt (rmaxsize, maxsize))
+			  {
+			    /* If we know an upper bound below the declared
+			       one this is no longer variable.  */
+			    if (known_size_p (maxsize))
+			      seen_variable_array_ref = false;
+			    maxsize = rmaxsize;
+			  }
+		      }
+		    /* Try to adjust bit_offset with range information.  */
+		    offset_int omin
+		      = offset_int::from (min, TYPE_SIGN (TREE_TYPE (index)));
+		    if (known_le (lbound, omin))
+		      {
+			poly_offset_int woffset
+			  = wi::sext (omin - lbound,
+				      TYPE_PRECISION (TREE_TYPE (index)));
+			woffset *= wi::to_offset (unit_size);
+			woffset <<= LOG2_BITS_PER_UNIT;
+			bit_offset += woffset;
+			if (known_size_p (maxsize))
+			  maxsize -= woffset;
+		      }
+		  }
 	      }
 	  }
 	  break;