re PR tree-optimization/72817 (wrong code at -O3 on x86_64-linux-gnu (in both…

re PR tree-optimization/72817 (wrong code at -O3 on x86_64-linux-gnu (in both 32-bit and 64-bit modes))

	PR tree-optimization/72817
	PR tree-optimization/73450
	* tree-ssa-loop-niter.c (number_of_iterations_ne): Check
	multiple_of_p for adjusted IV.base.

	gcc/testsuite
	* gcc.dg/tree-ssa/pr72817.c: New test.
	* gcc.dg/tree-ssa/pr73450.c: New test.

From-SVN: r239494

gcc/ChangeLog

+2016-08-16  Bin Cheng  <bin.cheng@arm.com>
+
+	PR tree-optimization/72817
+	PR tree-optimization/73450
+	* tree-ssa-loop-niter.c (number_of_iterations_ne): Check
+	multiple_of_p for adjusted IV.base.
+
 2016-08-15  Uros Bizjak  <ubizjak@gmail.com>
 
 	PR target/72867

gcc/testsuite/ChangeLog

+2016-08-16  Bin Cheng  <bin.cheng@arm.com>
+
+	PR tree-optimization/72817
+	PR tree-optimization/73450
+	* gcc.dg/tree-ssa/pr72817.c: New test.
+	* gcc.dg/tree-ssa/pr73450.c: New test.
+
 2016-08-15  Fritz Reese  <fritzoreese@gmail.com>
 
 	* gfortran.dg/init_flag_13.f90: New testcase.

gcc/testsuite/gcc.dg/tree-ssa/pr72817.c

+/* { dg-do run } */
+/* { dg-options "-O3" } */
+
+char a;
+short b;
+
+int main ()
+{
+  for (a = 3; a != -1; a -= 5)
+    while (b)
+      ;
+  return 0;
+}

gcc/testsuite/gcc.dg/tree-ssa/pr73450.c

+/* { dg-do run } */
+/* { dg-options "-O3" } */
+
+int a;
+char b;
+int main() {
+  char c = 0;
+  for (; c != 3; c = c + 7) {
+    a = b & a;
+    if (a)
+      break;
+  }
+  return 0;
+}

gcc/tree-ssa-loop-niter.c

@@ -999,33 +999,36 @@ number_of_iterations_ne (struct loop *loop, tree type, affine_iv *iv,
   mpz_clear (max);
 
   /* Compute no-overflow information for the control iv.  This can be
-     proven when below two conditions hold.
-
-       1) |FINAL - base| is an exact multiple of step.
-       2) IV evaluates toward FINAL at beginning, i.e:
+     proven when below two conditions are satisfied:
 
+       1) IV evaluates toward FINAL at beginning, i.e:
 	    base <= FINAL ; step > 0
 	    base >= FINAL ; step < 0
 
-	  Note the first condition holds, the second can be then relaxed
-	  to below condition.
+       2) |FINAL - base| is an exact multiple of step.
+
+     Unfortunately, it's hard to prove above conditions after pass loop-ch
+     because loop with exit condition (IV != FINAL) usually will be guarded
+     by initial-condition (IV.base - IV.step != FINAL).  In this case, we
+     can alternatively try to prove below conditions:
 
-	    base - step < FINAL ; step > 0
+       1') IV evaluates toward FINAL at beginning, i.e:
+	    new_base = base - step < FINAL ; step > 0
 					     && base - step doesn't underflow
-	    base - step > FINAL ; step < 0
+	    new_base = base - step > FINAL ; step < 0
 					     && base - step doesn't overflow
 
-	  The relaxation is important because after pass loop-ch, loop
-	  with exit condition (IV != FINAL) will usually be guarded by
-	  pre-condition (IV.base - IV.step != FINAL).  Please refer to
-	  PR34114 as an example.
+       2') |FINAL - new_base| is an exact multiple of step.
+
+     Please refer to PR34114 as an example of loop-ch's impact, also refer
+     to PR72817 as an example why condition 2') is necessary.
 
-     Also note, for NE_EXPR, base equals to FINAL is a special case, in
+     Note, for NE_EXPR, base equals to FINAL is a special case, in
      which the loop exits immediately, and the iv does not overflow.  */
   if (!niter->control.no_overflow
       && (integer_onep (s) || multiple_of_p (type, c, s)))
     {
-      tree t, cond, relaxed_cond = boolean_false_node;
+      tree t, cond, new_c, relaxed_cond = boolean_false_node;
 
       if (tree_int_cst_sign_bit (iv->step))
 	{
@@ -1039,6 +1042,10 @@ number_of_iterations_ne (struct loop *loop, tree type, affine_iv *iv,
 	      if (integer_nonzerop (t))
 		{
 		  t = fold_build2 (MINUS_EXPR, type, iv->base, iv->step);
+		  new_c = fold_build2 (MINUS_EXPR, niter_type,
+				       fold_convert (niter_type, t),
+				       fold_convert (niter_type, final));
+		  if (multiple_of_p (type, new_c, s))
 		    relaxed_cond = fold_build2 (GT_EXPR, boolean_type_node,
 						t, final);
 		}
@@ -1056,6 +1063,10 @@ number_of_iterations_ne (struct loop *loop, tree type, affine_iv *iv,
 	      if (integer_nonzerop (t))
 		{
 		  t = fold_build2 (MINUS_EXPR, type, iv->base, iv->step);
+		  new_c = fold_build2 (MINUS_EXPR, niter_type,
+				       fold_convert (niter_type, final),
+				       fold_convert (niter_type, t));
+		  if (multiple_of_p (type, new_c, s))
 		    relaxed_cond = fold_build2 (LT_EXPR, boolean_type_node,
 						t, final);
 		}