PR tree-optimization/90879 - fold zero-equality of strcmp between a longer string and a smaller array

gcc/c-family/ChangeLog:

	PR tree-optimization/90879
	* c.opt (-Wstring-compare): New option.

gcc/testsuite/ChangeLog:

	PR tree-optimization/90879
	* gcc.dg/Wstring-compare-2.c: New test.
	* gcc.dg/Wstring-compare.c: New test.
	* gcc.dg/strcmpopt_3.c: Scan the optmized dump instead of strlen.
	* gcc.dg/strcmpopt_6.c: New test.
	* gcc.dg/strlenopt-65.c: Remove uinnecessary declarations, add
	test cases.
	* gcc.dg/strlenopt-66.c: Run it.
	* gcc.dg/strlenopt-68.c: New test.

gcc/ChangeLog:

	PR tree-optimization/90879
	* builtins.c (check_access): Avoid using maxbound when null.
	* calls.c (maybe_warn_nonstring_arg): Adjust to get_range_strlen change.
	* doc/invoke.texi (-Wstring-compare): Document new warning option.
	* gimple-fold.c (get_range_strlen_tree): Make setting maxbound
	conditional.
	(get_range_strlen): Overwrite initial maxbound when non-null.
	* gimple-ssa-sprintf.c (get_string_length): Adjust to get_range_strlen
	changes.
	* tree-ssa-strlen.c (maybe_diag_stxncpy_trunc): Same.
	(used_only_for_zero_equality): New function.
	(handle_builtin_memcmp): Call it.
	(determine_min_objsize): Return an integer instead of tree.
	(get_len_or_size, strxcmp_eqz_result): New functions.
	(maybe_warn_pointless_strcmp): New function.
	(handle_builtin_string_cmp): Call it.  Fold zero-equality of strcmp
	between a longer string and a smaller array.
	(get_range_strlen_dynamic): Overwrite initial maxbound when non-null.

From-SVN: r276773

1 files changed, 24 insertions, 20 deletions

diff --git a/gcc/gimple-ssa-sprintf.c b/gcc/gimple-ssa-sprintf.c
index b11d798..b548bbd 100644
--- a/gcc/gimple-ssa-sprintf.c
+++ b/gcc/gimple-ssa-sprintf.c
@@ -1974,8 +1974,11 @@ get_string_length (tree str, unsigned eltsize, const vr_values *vr)
   if (!str)
     return fmtresult ();
 
-  /* Try to determine the dynamic string length first.  */
+  /* Try to determine the dynamic string length first.
+     Set MAXBOUND to an arbitrary non-null non-integer node as a request
+     to have it set to the length of the longest string in a PHI.  */
   c_strlen_data lendata = { };
+  lendata.maxbound = str;
   if (eltsize == 1)
     get_range_strlen_dynamic (str, &lendata, vr);
   else
@@ -1988,26 +1991,27 @@ get_string_length (tree str, unsigned eltsize, const vr_values *vr)
       get_range_strlen (str, &lendata, eltsize);
     }
 
-  /* LENDATA.MAXBOUND is null when LENDATA.MIN corresponds to the shortest
-     string referenced by STR.  Otherwise, if it's not equal to .MINLEN it
-     corresponds to the bound of the largest array STR refers to, if known,
-     or it's SIZE_MAX otherwise.  */
+  /* If LENDATA.MAXBOUND is not equal to .MINLEN it corresponds to the bound
+     of the largest array STR refers to, if known, or it's set to SIZE_MAX
+     otherwise.  */
 
   /* Return the default result when nothing is known about the string.  */
-  if (lendata.maxbound)
+  if ((lendata.maxbound && !tree_fits_uhwi_p (lendata.maxbound))
+      || !tree_fits_uhwi_p (lendata.maxlen))
     {
-      if (integer_all_onesp (lendata.maxbound)
-      	  && integer_all_onesp (lendata.maxlen))
-      	return fmtresult ();
-
-      if (!tree_fits_uhwi_p (lendata.maxbound)
-	  || !tree_fits_uhwi_p (lendata.maxlen))
-      	return fmtresult ();
-
-      unsigned HOST_WIDE_INT lenmax = tree_to_uhwi (max_object_size ()) - 2;
-      if (lenmax <= tree_to_uhwi (lendata.maxbound)
-	  && lenmax <= tree_to_uhwi (lendata.maxlen))
-	return fmtresult ();
+      fmtresult res;
+      res.nonstr = lendata.decl;
+      return res;
+    }
+
+  unsigned HOST_WIDE_INT lenmax = tree_to_uhwi (max_object_size ()) - 2;
+  if (integer_zerop (lendata.minlen)
+      && (!lendata.maxbound || lenmax <= tree_to_uhwi (lendata.maxbound))
+      && lenmax <= tree_to_uhwi (lendata.maxlen))
+    {
+      fmtresult res;
+      res.nonstr = lendata.decl;
+      return res;
     }
 
   HOST_WIDE_INT min
@@ -2056,9 +2060,9 @@ get_string_length (tree str, unsigned eltsize, const vr_values *vr)
     {
       /* When the upper bound is unknown (it can be zero or excessive)
 	 set the likely length to the greater of 1.  If MAXBOUND is
-	 set, also reset the length of the lower bound to zero.  */
+	 known, also reset the length of the lower bound to zero.  */
       res.range.likely = res.range.min ? res.range.min : warn_level > 1;
-      if (lendata.maxbound)
+      if (lendata.maxbound && !integer_all_onesp (lendata.maxbound))
 	res.range.min = 0;
     }