x86: Add gcc.target/i386/strncmp-1.c

Add a strncmp test for the cmpstrn pattern with neither of the strings
is a constant string.  We can expand the cmpstrn pattern to "repz cmpsb"
only if one of the strings is a constant so that expand_builtin_strncmp()
can write the length argument to be the minimum of the const string
length and the actual length argument.  Otherwise, "repz cmpsb" may pass
the 0 byte.

	* gcc.target/i386/strncmp-1.c: New test.

2 files changed, 51 insertions, 0 deletions

diff --git a/gcc/testsuite/ChangeLog b/gcc/testsuite/ChangeLog
index 9d757c4..fa3d018 100644
--- a/gcc/testsuite/ChangeLog
+++ b/gcc/testsuite/ChangeLog
@@ -1,3 +1,7 @@
+2020-05-17  H.J. Lu  <hongjiu.lu@intel.com>
+
+	* gcc.target/i386/strncmp-1.c: New test.
+
 2020-05-16  Iain Sandoe  <iain@sandoe.co.uk>
 
 	* g++.dg/coroutines/co-return-syntax-10-movable.C: New test.
diff --git a/gcc/testsuite/gcc.target/i386/strncmp-1.c b/gcc/testsuite/gcc.target/i386/strncmp-1.c
new file mode 100644
index 0000000..044fc5c
--- /dev/null
+++ b/gcc/testsuite/gcc.target/i386/strncmp-1.c
@@ -0,0 +1,47 @@
+/* { dg-do run { target mmap } } */
+/* { dg-options "-O2" } */
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+#include <sys/mman.h>
+
+#ifndef MAP_ANONYMOUS
+#define MAP_ANONYMOUS MAP_ANON
+#endif
+
+int
+__attribute__ ((noclone, noinline))
+compare (char *d, char *s, unsigned int l)
+{
+  return __builtin_strncmp (d, s, l);
+}
+
+int
+main ()
+{
+  size_t page_size = sysconf(_SC_PAGESIZE);
+  char *buf = mmap (0, 2 * page_size, PROT_READ | PROT_WRITE,
+		    MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
+  if (buf == MAP_FAILED)
+    {
+      perror ("mmap");
+      abort ();
+    }
+
+  if (mprotect (buf + page_size, page_size, PROT_NONE))
+    {
+      perror ("mprotect");
+      abort ();
+    }
+
+  char *src1 = buf + page_size - sizeof ("foo");
+  char *src2 = buf;
+  memcpy (src1, "foo", sizeof ("foo"));
+  memcpy (src2, "foo", sizeof ("foo"));
+  int result = compare (src1, src2, sizeof ("foo") + 16);
+  if (result != 0)
+    abort ();
+  return 0;
+}