[committed] Minor logic cleanup in get_range_strlen

[Jeff Law <law at redhat dot com>]

Just a trivial cleanup from Martin's work.

if (x == CONST)
  do something;
else
  return value;

Turns into

if (x != CONST)
  return value;
do something;


Again no behavior changes, but makes it easier to find the nuggets in
the rest of Martin's work.

Bootstrapped, regression tested on x86_64 and installed on the trunk.

jeff

ps. We're just about done with this stuff :-)  The holidays are both a
blessing and a curse when it comes to wrapping up something like this...

commit 0d90d6a22287cecf0c509336005cfd6c27560c67
Author: Jeff Law <law@torsion.usersys.redhat.com>
Date:   Fri Dec 21 14:23:49 2018 -0500

            * gimple-fold.c (get_range_strlen): Minor logic cleanup.  Add comments
            on code's intent.

diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index 1ee865e1de8..54585381cbe 100644
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,6 +1,9 @@
 2018-12-30  Martin Sebor  <msebor@redhat.com>
 	    Jeff Law  <law@redhat.com>
 
+	* gimple-fold.c (get_range_strlen): Minor logic cleanup.  Add comments
+	on code's intent.
+
 	* gimple-fold.c (strlen_range_kind): New enum.
 	(get_range_strlen): Update signature to use strlen_range_kind
 	instead of type+fuzzy.
diff --git a/gcc/gimple-fold.c b/gcc/gimple-fold.c
index 76fa328703c..fb43552bc35 100644
--- a/gcc/gimple-fold.c
+++ b/gcc/gimple-fold.c
@@ -1548,10 +1548,17 @@ get_range_strlen (tree arg, tree length[2], bitmap *visited,
 	      if (!get_range_strlen (ops[i], length, visited, rkind,
 				     flexp, eltsize, nonstr))
 		{
-		  if (rkind == SRK_LENRANGE_2)
-		    *maxlen = build_all_ones_cst (size_type_node);
-		  else
+		  if (rkind != SRK_LENRANGE_2)
 		    return false;
+		  /* Set the upper bound to the maximum to prevent
+		     it from being adjusted in the next iteration but
+		     leave MINLEN and the more conservative MAXBOUND
+		     determined so far alone (or leave them null if
+		     they haven't been set yet).  That the MINLEN is
+		     in fact zero can be determined from MAXLEN being
+		     unbounded but the discovered minimum is used for
+		     diagnostics.  */
+		  *maxlen = build_all_ones_cst (size_type_node);
 		}
 	    return true;
 	  }
@@ -1576,10 +1583,17 @@ get_range_strlen (tree arg, tree length[2], bitmap *visited,
 	    if (!get_range_strlen (arg, length, visited, rkind, flexp,
 				   eltsize, nonstr))
 	      {
-		if (rkind == SRK_LENRANGE_2)
-		  *maxlen = build_all_ones_cst (size_type_node);
-		else
+		if (rkind != SRK_LENRANGE_2)
 		  return false;
+		/* Set the upper bound to the maximum to prevent
+		   it from being adjusted in the next iteration but
+		   leave MINLEN and the more conservative MAXBOUND
+		   determined so far alone (or leave them null if
+		   they haven't been set yet).  That the MINLEN is
+		   in fact zero can be determined from MAXLEN being
+		   unbounded but the discovered minimum is used for
+		   diagnostics.  */
+		*maxlen = build_all_ones_cst (size_type_node);
 	      }
           }
         return true;