[PATCH, PR tree-optimization/64277] Improve loop iterations count estimation

[Ilya Enkovich]

Hi,

This patch was supposed to fix PR tree-optimization/64277.  Tracker is now 
fixed by warnings disabling but I think patch is still useful to avoid dead 
code generated by complete unroll.

Bootstrapped and tested on x86_64-unknown-linux-gnu.

Thanks,
Ilya
--
gcc/

2015-01-27  Ilya Enkovich  <ilya.enkov...@intel.com>

        * tree-ssa-loop-niter.c (record_nonwrapping_iv): Use base
        range info when possible to refine estimation.

gcc/testsuite/

2015-01-27  Ilya Enkovich  <ilya.enkov...@intel.com>

        * gcc.dg/pr64277.c: New.


diff --git a/gcc/testsuite/gcc.dg/pr64277.c b/gcc/testsuite/gcc.dg/pr64277.c
new file mode 100644
index 0000000..0d5ef11
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/pr64277.c
@@ -0,0 +1,21 @@
+/* PR tree-optimization/64277 */
+/* { dg-do compile } */
+/* { dg-options "-O3 -Wall -Werror" } */
+
+
+int f1[10];
+void test1 (short a[], short m, unsigned short l)
+{
+  int i = l;
+  for (i = i + 5; i < m; i++)
+    f1[i] = a[i]++;
+}
+
+void test2 (short a[], short m, short l)
+{
+  int i;
+  if (m > 5)
+    m = 5;
+  for (i = m; i > l; i--)
+    f1[i] = a[i]++;
+}
diff --git a/gcc/tree-ssa-loop-niter.c b/gcc/tree-ssa-loop-niter.c
index 919f5c0..6a55c6f 100644
--- a/gcc/tree-ssa-loop-niter.c
+++ b/gcc/tree-ssa-loop-niter.c
@@ -2754,6 +2754,7 @@ record_nonwrapping_iv (struct loop *loop, tree base, tree 
step, gimple stmt,
 {
   tree niter_bound, extreme, delta;
   tree type = TREE_TYPE (base), unsigned_type;
+  tree orig_base = base;
 
   if (TREE_CODE (step) != INTEGER_CST || integer_zerop (step))
     return;
@@ -2777,16 +2778,32 @@ record_nonwrapping_iv (struct loop *loop, tree base, 
tree step, gimple stmt,
 
   if (tree_int_cst_sign_bit (step))
     {
+      wide_int min, max;
       extreme = fold_convert (unsigned_type, low);
-      if (TREE_CODE (base) != INTEGER_CST)
+      if (TREE_CODE (orig_base) == SSA_NAME
+         && TREE_CODE (high) == INTEGER_CST
+         && !POINTER_TYPE_P (TREE_TYPE (orig_base))
+         && SSA_NAME_RANGE_INFO (orig_base)
+         && get_range_info (orig_base, &min, &max) == VR_RANGE
+         && wi::gts_p (wide_int (high), max))
+       base = wide_int_to_tree (unsigned_type, max);
+      else if (TREE_CODE (base) != INTEGER_CST)
        base = fold_convert (unsigned_type, high);
       delta = fold_build2 (MINUS_EXPR, unsigned_type, base, extreme);
       step = fold_build1 (NEGATE_EXPR, unsigned_type, step);
     }
   else
     {
+      wide_int min, max;
       extreme = fold_convert (unsigned_type, high);
-      if (TREE_CODE (base) != INTEGER_CST)
+      if (TREE_CODE (orig_base) == SSA_NAME
+         && TREE_CODE (low) == INTEGER_CST
+         && !POINTER_TYPE_P (TREE_TYPE (orig_base))
+         && SSA_NAME_RANGE_INFO (orig_base)
+         && get_range_info (orig_base, &min, &max) == VR_RANGE
+         && wi::gts_p (min, wide_int (low)))
+       base = wide_int_to_tree (unsigned_type, min);
+      else if (TREE_CODE (base) != INTEGER_CST)
        base = fold_convert (unsigned_type, low);
       delta = fold_build2 (MINUS_EXPR, unsigned_type, extreme, base);
     }