re PR tree-optimization/84648 (Missed optimization : loop not removed.)

PR tree-optimization/84648
	* tree-ssa-loop-niter.c (adjust_cond_for_loop_until_wrap): New.
	(number_of_iterations_cond): Adjust exit cond for loop-until-wrap case
	by calling adjust_cond_for_loop_until_wrap.

	gcc/testsuite
	* gcc.dg/tree-ssa/pr84648.c: New test.
	* gcc.dg/pr68317.c: Add warning check on overflow.

From-SVN: r266171

gcc/ChangeLog

@@ -1,3 +1,10 @@
+2018-11-15  Bin Cheng  <bin.cheng@linux.alibaba.com>
+
+	PR tree-optimization/84648
+	* tree-ssa-loop-niter.c (adjust_cond_for_loop_until_wrap): New.
+	(number_of_iterations_cond): Adjust exit cond for loop-until-wrap case
+	by calling adjust_cond_for_loop_until_wrap.
+
 2018-11-15  Sandra Loosemore  <sandra@codesourcery.com>
 
 	PR other/56334

gcc/testsuite/ChangeLog

@@ -1,3 +1,9 @@
+2018-11-15  Bin Cheng  <bin.cheng@linux.alibaba.com>
+
+	PR tree-optimization/84648
+	* gcc.dg/tree-ssa/pr84648.c: New test.
+	* gcc.dg/pr68317.c: Add warning check on overflow.
+
 2018-11-14  Nathan Sidwell  <nathan@acm.org>
 
 	PR debug/88006

gcc/testsuite/gcc.dg/pr68317.c

@@ -11,5 +11,5 @@ foo ()
  for (index; index <= 10; index--)
    /* Result of the following multiply will overflow
       when converted to signed int.  */
-   bar ((0xcafe + index) * 0xdead);
+   bar ((0xcafe + index) * 0xdead);  /* { dg-warning "iteration \[0-9\]+ invokes undefined behavior" } */
 }

gcc/testsuite/gcc.dg/tree-ssa/pr84648.c

@@ -0,0 +1,10 @@
+/* { dg-do compile } */
+/* { dg-options "-O3 -fdump-tree-cddce1-details" } */
+
+int main() {
+    for (unsigned i = 0; i < (1u << 31); ++i) {
+    }
+    return 0;
+}
+
+/* { dg-final { scan-tree-dump-times "Found loop 1 to be finite: upper bound found" 1 "cddce1" } } */

gcc/tree-ssa-loop-niter.c

@@ -1641,6 +1641,62 @@ dump_affine_iv (FILE *file, affine_iv *iv)
     }
 }
 
+/* Given exit condition IV0 CODE IV1 in TYPE, this function adjusts
+   the condition for loop-until-wrap cases.  For example:
+     (unsigned){8, -1}_loop < 10        => {0, 1} != 9
+     10 < (unsigned){0, max - 7}_loop   => {0, 1} != 8
+   Return true if condition is successfully adjusted.  */
+
+static bool
+adjust_cond_for_loop_until_wrap (tree type, affine_iv *iv0, tree_code *code,
+				 affine_iv *iv1)
+{
+  /* Only support simple cases for the moment.  */
+  if (TREE_CODE (iv0->base) != INTEGER_CST
+      || TREE_CODE (iv1->base) != INTEGER_CST)
+    return false;
+
+  tree niter_type = unsigned_type_for (type), high, low;
+  /* Case: i-- < 10.  */
+  if (integer_zerop (iv1->step))
+    {
+      /* TODO: Should handle case in which abs(step) != 1.  */
+      if (!integer_minus_onep (iv0->step))
+	return false;
+      /* Give up on infinite loop.  */
+      if (*code == LE_EXPR
+	  && tree_int_cst_equal (iv1->base, TYPE_MAX_VALUE (type)))
+	return false;
+      high = fold_build2 (PLUS_EXPR, niter_type,
+			  fold_convert (niter_type, iv0->base),
+			  build_int_cst (niter_type, 1));
+      low = fold_convert (niter_type, TYPE_MIN_VALUE (type));
+    }
+  else if (integer_zerop (iv0->step))
+    {
+      /* TODO: Should handle case in which abs(step) != 1.  */
+      if (!integer_onep (iv1->step))
+	return false;
+      /* Give up on infinite loop.  */
+      if (*code == LE_EXPR
+	  && tree_int_cst_equal (iv0->base, TYPE_MIN_VALUE (type)))
+	return false;
+      high = fold_convert (niter_type, TYPE_MAX_VALUE (type));
+      low = fold_build2 (MINUS_EXPR, niter_type,
+			 fold_convert (niter_type, iv1->base),
+			 build_int_cst (niter_type, 1));
+    }
+  else
+    gcc_unreachable ();
+
+  iv0->base = low;
+  iv0->step = fold_convert (niter_type, integer_one_node);
+  iv1->base = high;
+  iv1->step = build_int_cst (niter_type, 0);
+  *code = NE_EXPR;
+  return true;
+}
+
 /* Determine the number of iterations according to condition (for staying
    inside loop) which compares two induction variables using comparison
    operator CODE.  The induction variable on left side of the comparison
@@ -1764,16 +1820,6 @@ number_of_iterations_cond (struct loop *loop,
   if (integer_zerop (iv0->step) && integer_zerop (iv1->step))
     return false;
 
-  /* Ignore loops of while (i-- < 10) type.  */
-  if (code != NE_EXPR)
-    {
-      if (iv0->step && tree_int_cst_sign_bit (iv0->step))
-	return false;
-
-      if (!integer_zerop (iv1->step) && !tree_int_cst_sign_bit (iv1->step))
-	return false;
-    }
-
   /* If the loop exits immediately, there is nothing to do.  */
   tree tem = fold_binary (code, boolean_type_node, iv0->base, iv1->base);
   if (tem && integer_zerop (tem))
@@ -1783,6 +1829,15 @@ number_of_iterations_cond (struct loop *loop,
       return true;
     }
 
+  /* Handle special case loops: while (i-- < 10) and while (10 < i++) by
+     adjusting iv0, iv1 and code.  */
+  if (code != NE_EXPR
+      && (tree_int_cst_sign_bit (iv0->step)
+	  || (!integer_zerop (iv1->step)
+	      && !tree_int_cst_sign_bit (iv1->step)))
+      && !adjust_cond_for_loop_until_wrap (type, iv0, &code, iv1))
+    return false;
+
   /* OK, now we know we have a senseful loop.  Handle several cases, depending
      on what comparison operator is used.  */
   bound_difference (loop, iv1->base, iv0->base, &bnds);