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[committed] Small warning bugfix

This was extracted from Martin's work on the strlen range fixes.

As the comment indicates, avoid warning for strncpy (a, b, N) where
N == sizeof (a) and N == sizeof (b).

I didn't immediately see a testcase in Martin's changes.  I'm pretty
sure I've seen a few Fedora rawhide packages failing builds because of
this issue.

Bootstrapped & regression tested on x86_64.  Installing on the trunk.
My Fedora tester will pick it up at the next snapshot.  My GCC tester
will pick it up overnight.


commit b74ab41ec0b6f590d0c5ff803b42a05b21fb2218
Author: law <law@138bc75d-0d04-0410-961f-82ee72b054a4>
Date:   Fri Dec 28 19:26:14 2018 +0000

            * tree-ssa-strlen.c (maybe_diag_stxncpy_trunc): Avoid
            undesirable warning.
    git-svn-id: svn+ssh:// 138bc75d-0d04-0410-961f-82ee72b054a4

diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index 741c02d6cda..e79809c50f6 100644
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,8 @@
+2018-12-28  Martin Sebor  <>
+	* tree-ssa-strlen.c (maybe_diag_stxncpy_trunc): Avoid
+	undesirable warning.
 2018-12-28  Thomas Schwinge  <>
 	* omp-expand.c (expand_omp_target): Restructure OpenACC vs. OpenMP
diff --git a/gcc/tree-ssa-strlen.c b/gcc/tree-ssa-strlen.c
index 669c315dce2..c74ce0feac5 100644
--- a/gcc/tree-ssa-strlen.c
+++ b/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",

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