[glibc/grte_v5] More aggressively prevent a buffer from being optimized out

[glibc/grte_v5] More aggressively prevent a buffer from being optimized out

[Shu-Chun Weng]

https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=7903140dcc2b36c4eadae7132fb51a4463fd134e

commit 7903140dcc2b36c4eadae7132fb51a4463fd134e
Author: Shu-Chun Weng <scw@google.com>
Date:   Mon May 3 16:12:44 2021 -0700

    More aggressively prevent a buffer from being optimized out
    
    The volatile global variable was first introduced in e86f9654c. I have
    noticed the compiler still optimizing the buffer out on AArch64
    presumably because the assignment is after all other observable
    behaviors so it's still valid to eliminate it.

Diff:
---
 string/tst-xbzero-opt.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/string/tst-xbzero-opt.c b/string/tst-xbzero-opt.c
index e9c411b2ef..4f16c4d678 100644
--- a/string/tst-xbzero-opt.c
+++ b/string/tst-xbzero-opt.c
@@ -119,17 +119,17 @@ static void
 setup_no_clear (void)
 {
   unsigned char buf[TEST_BUFFER_SIZE];
-  prepare_test_buffer (buf);
   vol_glob = buf;
+  prepare_test_buffer (buf);
 }
 
 static void
 setup_ordinary_clear (void)
 {
   unsigned char buf[TEST_BUFFER_SIZE];
+  vol_glob = buf;
   prepare_test_buffer (buf);
   memset (buf, 0, TEST_BUFFER_SIZE);
-  vol_glob = buf;
 }
 
 static void