re PR tree-optimization/18048 (mgrid loop performance regression with ivopts (register pressure))

	PR tree-optimization/18048
	* fold-const.c (try_move_mult_to_index): New function.
	(fold): Use try_move_mult_to_index.
	* tree-ssa-loop-ivopts.c (try_add_cand_for): Prefer common candidates.
	* tree-ssa-loop-niter.c (number_of_iterations_cond): Produce
	an all-ones unsigned constant without extra bits.
	* tree.c (build_low_bits_mask): New function.
	* tree.h (build_low_bits_mask): Declare.

From-SVN: r89708

1 files changed, 34 insertions, 0 deletions

diff --git a/gcc/tree.c b/gcc/tree.c
index 18dec5e..9531e69 100644
--- a/gcc/tree.c
+++ b/gcc/tree.c
@@ -609,6 +609,40 @@ build_int_cst_wide (tree type, unsigned HOST_WIDE_INT low, HOST_WIDE_INT hi)
   return t;
 }
 
+/* Builds an integer constant in TYPE such that lowest BITS bits are ones
+   and the rest are zeros.  */
+
+tree
+build_low_bits_mask (tree type, unsigned bits)
+{
+  unsigned HOST_WIDE_INT low;
+  HOST_WIDE_INT high;
+  unsigned HOST_WIDE_INT all_ones = ~(unsigned HOST_WIDE_INT) 0;
+
+  gcc_assert (bits <= TYPE_PRECISION (type));
+
+  if (bits == TYPE_PRECISION (type)
+      && !TYPE_UNSIGNED (type))
+    {
+      /* Sign extended all-ones mask.  */
+      low = all_ones;
+      high = -1;
+    }
+  else if (bits <= HOST_BITS_PER_WIDE_INT)
+    {
+      low = all_ones >> (HOST_BITS_PER_WIDE_INT - bits);
+      high = 0;
+    }
+  else
+    {
+      bits -= HOST_BITS_PER_WIDE_INT;
+      low = all_ones;
+      high = all_ones >> (HOST_BITS_PER_WIDE_INT - bits);
+    }
+
+  return build_int_cst_wide (type, low, high);
+}
+
 /* Checks that X is integer constant that can be expressed in (unsigned)
    HOST_WIDE_INT without loss of precision.  */