tree-ssa-strlen.c (maybe_diag_stxncpy_trunc): Avoid undesirable warning.

	* tree-ssa-strlen.c (maybe_diag_stxncpy_trunc): Avoid
	undesirable warning.

From-SVN: r267454

gcc/ChangeLog

+2018-12-28  Martin Sebor  <msebor@redhat.com>
+
+	* tree-ssa-strlen.c (maybe_diag_stxncpy_trunc): Avoid
+	undesirable warning.
+
 2018-12-28  Thomas Schwinge  <thomas@codesourcery.com>
 
 	* omp-expand.c (expand_omp_target): Restructure OpenACC vs. OpenMP

gcc/tree-ssa-strlen.c

@@ -2114,6 +2114,13 @@ maybe_diag_stxncpy_trunc (gimple_stmt_iterator gsi, tree src, tree cnt)
       if (wi::to_wide (dstsize) != cntrange[1])
 	return false;
 
+      /* Avoid warning for strncpy(a, b, N) calls where the following
+	 equalities hold:
+	   N == sizeof a && N == sizeof b */
+      if (tree srcsize = compute_objsize (src, 1))
+	if (wi::to_wide (srcsize) == cntrange[1])
+	  return false;
+
       if (cntrange[0] == cntrange[1])
 	return warning_at (callloc, OPT_Wstringop_truncation,
 			   "%G%qD specified bound %E equals destination size",