[PATCH 3/4] string: Suppress -Wmaybe-unitialized for wordcopy [BZ #19444]

[Adhemerval Zanella <adhemerval.zanella@linaro.org>]

With GCC 6+ when compiling with -O1 warns that some MERGE macro usage
might be used uninitialized.  The issue is calling the function with
len equal to 0 is undefined since the first 'switch' will not trigger
any case and then subsequent loop will potentially use uninitialized
variables.

However all usages on mem routines always called the function for
sizes larger than OP_T_THRES.
---
 string/wordcopy.c | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)

diff --git a/string/wordcopy.c b/string/wordcopy.c
index d05718322c..3b6344115d 100644
--- a/string/wordcopy.c
+++ b/string/wordcopy.c
@@ -18,8 +18,19 @@
 
 /* BE VERY CAREFUL IF YOU CHANGE THIS CODE...!  */
 
+#include <assert.h>
 #include <stddef.h>
+#include <libc-diag.h>
+/* With GCC 6 when compiling with -O1 warns that some MERGE macro usage might
+   be used uninitialized.  The issue is calling the function with len equal to
+   0 is undefined since the first 'switch' will not trigger any case and then
+   subsequent loop will potentially use uninitialized variables.  However all
+   usages on mem routines always called the function for sizes larger than
+   OP_T_THRES.  */
+DIAG_PUSH_NEEDS_COMMENT;
+DIAG_IGNORE_NEEDS_COMMENT (6, "-Wmaybe-uninitialized");
 #include <memcopy.h>
+DIAG_POP_NEEDS_COMMENT;
 
 /* _wordcopy_fwd_aligned -- Copy block beginning at SRCP to
    block beginning at DSTP with LEN `op_t' words (not LEN bytes!).
@@ -94,7 +105,11 @@ WORDCOPY_FWD_ALIGNED (long int dstp, long int srcp, size_t len)
     {
     do8:
       a0 = ((op_t *) srcp)[0];
+      /* Check the comment on memcopy.h inclusion.  */
+      DIAG_PUSH_NEEDS_COMMENT;
+      DIAG_IGNORE_NEEDS_COMMENT (6, "-Wmaybe-uninitialized");
       ((op_t *) dstp)[0] = a1;
+      DIAG_POP_NEEDS_COMMENT;
     do7:
       a1 = ((op_t *) srcp)[1];
       ((op_t *) dstp)[1] = a0;
@@ -291,7 +306,11 @@ WORDCOPY_BWD_ALIGNED (long int dstp, long int srcp, size_t len)
     {
     do8:
       a0 = ((op_t *) srcp)[7];
+      /* Check the comment on memcopy.h inclusion.  */
+      DIAG_PUSH_NEEDS_COMMENT;
+      DIAG_IGNORE_NEEDS_COMMENT (6, "-Wmaybe-uninitialized");
       ((op_t *) dstp)[7] = a1;
+      DIAG_POP_NEEDS_COMMENT;
     do7:
       a1 = ((op_t *) srcp)[6];
       ((op_t *) dstp)[6] = a0;
-- 
2.34.1