Remove H5_NO_ALIGNMENT_RESTRICTIONS (#1426)

* Do not conditionally compile code that uses a pointer dereference
and assignment to copy a potentially unaligned variable to aligned
automatic storage, or vice versa.  Instead, always use naked `memcpy(3)`s.
Disassembling the generated code reveals that the `memcpy(3)`s optimize
(`-O3`) to a single `mov` instruction for x86_64, which is not strict
about alignment.

This change reduces the size of code and scripts by 143 lines, eases
our way to cross-compilation, and avoids invoking undefined behavior.

* Committing clang-format changes

* Per discussion, use HD and add comments.

Co-authored-by: github-actions <41898282+github-actions[bot]@users.noreply.github.com>

1 files changed, 20 insertions, 74 deletions

diff --git a/src/H5Tvlen.c b/src/H5Tvlen.c
index 7bf28af..39d33d4 100644
--- a/src/H5Tvlen.c
+++ b/src/H5Tvlen.c
@@ -369,11 +369,7 @@ done:
 static herr_t
 H5T__vlen_mem_seq_getlen(H5VL_object_t H5_ATTR_UNUSED *file, const void *_vl, size_t *len)
 {
-#ifdef H5_NO_ALIGNMENT_RESTRICTIONS
-    const hvl_t *vl = (const hvl_t *)_vl; /* Pointer to the user's hvl_t information */
-#else
     hvl_t vl; /* User's hvl_t information */
-#endif
 
     FUNC_ENTER_PACKAGE_NOERR
 
@@ -381,13 +377,12 @@ H5T__vlen_mem_seq_getlen(H5VL_object_t H5_ATTR_UNUSED *file, const void *_vl, si
     HDassert(_vl);
     HDassert(len);
 
-#ifdef H5_NO_ALIGNMENT_RESTRICTIONS
-    *len = vl->len;
-#else
-    H5MM_memcpy(&vl, _vl, sizeof(hvl_t));
+    /* Copy to ensure correct alignment.  memcpy is best here because
+     * it optimizes to fast code.
+     */
+    HDmemcpy(&vl, _vl, sizeof(hvl_t));
 
     *len = vl.len;
-#endif
 
     FUNC_LEAVE_NOAPI(SUCCEED)
 } /* end H5T__vlen_mem_seq_getlen() */
@@ -407,25 +402,16 @@ H5T__vlen_mem_seq_getlen(H5VL_object_t H5_ATTR_UNUSED *file, const void *_vl, si
 static void *
 H5T__vlen_mem_seq_getptr(void *_vl)
 {
-#ifdef H5_NO_ALIGNMENT_RESTRICTIONS
-    const hvl_t *vl = (const hvl_t *)_vl; /* Pointer to the user's hvl_t information */
-#else
     hvl_t vl; /* User's hvl_t information */
-#endif
 
     FUNC_ENTER_PACKAGE_NOERR
 
     /* check parameters, return result */
-#ifdef H5_NO_ALIGNMENT_RESTRICTIONS
-    HDassert(vl);
-
-    FUNC_LEAVE_NOAPI(vl->p)
-#else
     HDassert(_vl);
-    H5MM_memcpy(&vl, _vl, sizeof(hvl_t));
+    /* Copy to ensure correct alignment. */
+    HDmemcpy(&vl, _vl, sizeof(hvl_t));
 
     FUNC_LEAVE_NOAPI(vl.p)
-#endif
 } /* end H5T__vlen_mem_seq_getptr() */
 
 /*-------------------------------------------------------------------------
@@ -443,24 +429,17 @@ H5T__vlen_mem_seq_getptr(void *_vl)
 static herr_t
 H5T__vlen_mem_seq_isnull(const H5VL_object_t H5_ATTR_UNUSED *file, void *_vl, hbool_t *isnull)
 {
-#ifdef H5_NO_ALIGNMENT_RESTRICTIONS
-    const hvl_t *vl = (const hvl_t *)_vl; /* Pointer to the user's hvl_t information */
-#else
     hvl_t vl; /* User's hvl_t information */
-#endif
 
     FUNC_ENTER_PACKAGE_NOERR
 
     /* Check parameters */
     HDassert(_vl);
 
-#ifdef H5_NO_ALIGNMENT_RESTRICTIONS
-    *isnull = ((vl->len == 0 || vl->p == NULL) ? TRUE : FALSE);
-#else
-    H5MM_memcpy(&vl, _vl, sizeof(hvl_t));
+    /* Copy to ensure correct alignment. */
+    HDmemcpy(&vl, _vl, sizeof(hvl_t));
 
     *isnull = ((vl.len == 0 || vl.p == NULL) ? TRUE : FALSE);
-#endif
 
     FUNC_LEAVE_NOAPI(SUCCEED)
 } /* end H5T__vlen_mem_seq_isnull() */
@@ -512,27 +491,18 @@ H5T__vlen_mem_seq_setnull(H5VL_object_t H5_ATTR_UNUSED *file, void *_vl, void H5
 static herr_t
 H5T__vlen_mem_seq_read(H5VL_object_t H5_ATTR_UNUSED *file, void *_vl, void *buf, size_t len)
 {
-#ifdef H5_NO_ALIGNMENT_RESTRICTIONS
-    const hvl_t *vl = (const hvl_t *)_vl; /* Pointer to the user's hvl_t information */
-#else
     hvl_t vl; /* User's hvl_t information */
-#endif
 
     FUNC_ENTER_PACKAGE_NOERR
 
     /* check parameters, copy data */
     HDassert(buf);
-#ifdef H5_NO_ALIGNMENT_RESTRICTIONS
-    HDassert(vl && vl->p);
-
-    H5MM_memcpy(buf, vl->p, len);
-#else
     HDassert(_vl);
-    H5MM_memcpy(&vl, _vl, sizeof(hvl_t));
+    /* Copy to ensure correct alignment. */
+    HDmemcpy(&vl, _vl, sizeof(hvl_t));
     HDassert(vl.p);
 
     H5MM_memcpy(buf, vl.p, len);
-#endif
 
     FUNC_LEAVE_NOAPI(SUCCEED)
 } /* end H5T__vlen_mem_seq_read() */
@@ -606,20 +576,15 @@ done:
 static herr_t
 H5T__vlen_mem_str_getlen(H5VL_object_t H5_ATTR_UNUSED *file, const void *_vl, size_t *len)
 {
-#ifdef H5_NO_ALIGNMENT_RESTRICTIONS
-    const char *s = *(const char *const *)_vl; /* Pointer to the user's string information */
-#else
     const char *s = NULL; /* Pointer to the user's string information */
-#endif
 
     FUNC_ENTER_PACKAGE_NOERR
 
     /* check parameters */
     HDassert(_vl);
 
-#ifndef H5_NO_ALIGNMENT_RESTRICTIONS
-    H5MM_memcpy(&s, _vl, sizeof(char *));
-#endif
+    /* Copy to ensure correct alignment. */
+    HDmemcpy(&s, _vl, sizeof(char *));
 
     *len = HDstrlen(s);
 
@@ -641,21 +606,14 @@ H5T__vlen_mem_str_getlen(H5VL_object_t H5_ATTR_UNUSED *file, const void *_vl, si
 static void *
 H5T__vlen_mem_str_getptr(void *_vl)
 {
-#ifdef H5_NO_ALIGNMENT_RESTRICTIONS
-    char *s = *(char **)_vl; /* Pointer to the user's string information */
-#else
-    char *      s = NULL; /* Pointer to the user's string information */
-#endif
+    char *s = NULL; /* Pointer to the user's string information */
 
     FUNC_ENTER_PACKAGE_NOERR
 
     /* check parameters */
-#ifdef H5_NO_ALIGNMENT_RESTRICTIONS
-    HDassert(s);
-#else
     HDassert(_vl);
-    H5MM_memcpy(&s, _vl, sizeof(char *));
-#endif
+    /* Copy to ensure correct alignment. */
+    HDmemcpy(&s, _vl, sizeof(char *));
 
     FUNC_LEAVE_NOAPI(s)
 } /* end H5T__vlen_mem_str_getptr() */
@@ -675,17 +633,12 @@ H5T__vlen_mem_str_getptr(void *_vl)
 static herr_t
 H5T__vlen_mem_str_isnull(const H5VL_object_t H5_ATTR_UNUSED *file, void *_vl, hbool_t *isnull)
 {
-#ifdef H5_NO_ALIGNMENT_RESTRICTIONS
-    char *s = *(char **)_vl; /* Pointer to the user's string information */
-#else
     char *s = NULL; /* Pointer to the user's string information */
-#endif
 
     FUNC_ENTER_PACKAGE_NOERR
 
-#ifndef H5_NO_ALIGNMENT_RESTRICTIONS
-    H5MM_memcpy(&s, _vl, sizeof(char *));
-#endif
+    /* Copy to ensure correct alignment. */
+    HDmemcpy(&s, _vl, sizeof(char *));
 
     *isnull = (s == NULL ? TRUE : FALSE);
 
@@ -732,23 +685,16 @@ H5T__vlen_mem_str_setnull(H5VL_object_t H5_ATTR_UNUSED *file, void *_vl, void H5
 static herr_t
 H5T__vlen_mem_str_read(H5VL_object_t H5_ATTR_UNUSED *file, void *_vl, void *buf, size_t len)
 {
-#ifdef H5_NO_ALIGNMENT_RESTRICTIONS
-    char *s = *(char **)_vl; /* Pointer to the user's string information */
-#else
-    char *s;        /* Pointer to the user's string information */
-#endif
+    char *s; /* Pointer to the user's string information */
 
     FUNC_ENTER_PACKAGE_NOERR
 
     if (len > 0) {
         /* check parameters */
         HDassert(buf);
-#ifdef H5_NO_ALIGNMENT_RESTRICTIONS
-        HDassert(s);
-#else
         HDassert(_vl);
-        H5MM_memcpy(&s, _vl, sizeof(char *));
-#endif
+        /* Copy to ensure correct alignment. */
+        HDmemcpy(&s, _vl, sizeof(char *));
 
         H5MM_memcpy(buf, s, len);
     } /* end if */