PR c/85931 - -Wsizeof-pointer-memaccess for strncpy with size of source

gcc/c-family/ChangeLog:

	PR c/85931
	* c-warn.c (sizeof_pointer_memaccess_warning): Avoid warning when
	sizeof source and destination yields the same value.

gcc/ChangeLog:

	PR c/85931
	* fold-const.c (operand_equal_p): Handle SAVE_EXPR.

gcc/testsuite/ChangeLog:

	PR c/85931
	* gcc.dg/Wstringop-truncation-3.c: New test.

From-SVN: r261515

2 files changed, 64 insertions, 0 deletions

diff --git a/gcc/testsuite/ChangeLog b/gcc/testsuite/ChangeLog
index 088f5c2..f9c8d93 100644
--- a/gcc/testsuite/ChangeLog
+++ b/gcc/testsuite/ChangeLog
@@ -1,3 +1,8 @@
+2018-06-12  Martin Sebor  <msebor@redhat.com>
+
+	PR c/85931
+	* gcc.dg/Wstringop-truncation-3.c: New test.
+
 2018-06-12  Will Schmidt  <will_schmidt@vnet.ibm.com>
 
 	* gcc.target/powerpc/p8-vec-xl-xst-v2.c: New.
diff --git a/gcc/testsuite/gcc.dg/Wstringop-truncation-3.c b/gcc/testsuite/gcc.dg/Wstringop-truncation-3.c
new file mode 100644
index 0000000..57f4d64
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/Wstringop-truncation-3.c
@@ -0,0 +1,59 @@
+/* PR c/85931 - -Wsizeof-pointer-memaccess for strncpy with size of source
+   { dg-do compile }
+   { dg-options "-O2 -Wall -Wstringop-truncation -ftrack-macro-expansion=0" } */
+
+typedef __SIZE_TYPE__ size_t;
+
+extern char* strncpy (char*, const char*, size_t);
+
+extern char a3[3], b3[3];
+extern char a5[5], b5[5];
+extern char ax[], bx[];
+
+struct SA
+{
+  char a3[3], b3[3];
+  char a5[5], b5[5];
+  char ax[];
+};
+
+void sink (void*, ...);
+
+#define T(d, s, n)   sink (strncpy (d, s, n))
+
+void test_array (unsigned n)
+{
+  T (a3, b3, 3);
+  /* For the following statemenmt, GCC 8.1 issues warning:
+
+       argument to ‘sizeof’ in ‘strncpy’ call is the same expression
+       as the source; did you mean to use the size of the destination?
+
+     Since the size of both the source and destination the warning
+     isn't helpful.  Verify that it isn't issued.  */
+  T (a3, b3, sizeof b3);    /* { dg-bogus "\\\[-Wsizeof-pointer-memaccess" } */
+
+  T (a3, ax, sizeof a3);    /* { dg-warning "\\\[-Wstringop-truncation" } */
+  T (ax, a3, sizeof a3);    /* { dg-warning "argument to .sizeof. in .strncpy. call is the same expression as the source" } */
+
+  char an[n], bn[n];
+  sink (an, bn);
+
+  T (an, bn, sizeof bn);    /* { dg-bogus "\\\[-Wsizeof-pointer-memaccess" } */
+}
+
+void test_member_array (struct SA *sa, unsigned n)
+{
+  T (sa->a3, sa->b3, 3);
+  T (sa->a3, sa->b3, sizeof sa->b3);  /* { dg-bogus "\\\[-Wsizeof-pointer-memaccess" } */
+
+  T (sa->a3, sa->ax, sizeof sa->a3);  /* { dg-warning "\\\[-Wstringop-truncation" } */
+  T (sa->ax, sa->a3, sizeof sa->a3);  /* { dg-warning "argument to .sizeof. in .strncpy. call is the same expression as the source" } */
+
+  struct VarLenStruct {
+    char an[n], bn[n];
+  } x;
+
+  sink (&x);
+  T (x.an, x.bn, sizeof x.bn);        /* { dg-bogus "\\\[-Wsizeof-pointer-memaccess" } */
+}