Re: [patch] Disable store merging in asan_expand_mark_ifn

[Eric Botcazou]

> Ok, stand corrected on that, 128-bit indeed, but even that is nothing not
> really used.

The irony is that I'm doing this for 32-bit SPARC (we cannot get ASAN to work 
in 64-bit mode for the time being) and the maximum alignment on 32-bit SPARC 
is 64-bit (even long doubles) so this will be totally unused. ;-)

> For STRICT_ALIGNMENT targets store merging pass obviously can't do anything
> with those, because unlike asan.c it can't figure out the alignment.

OK, revised patch attached.  I have manually verified that it yields the 
expected result for an array of long doubles on 64-bit SPARC.


2019-02-12  Eric Botcazou  <ebotca...@adacore.com>

        * asan.c (asan_expand_mark_ifn): Take into account the alignment of
        the object to pick the size of stores on strict-alignment platforms.

-- 
Eric Botcazou
Index: asan.c
===================================================================
--- asan.c	(revision 268508)
+++ asan.c	(working copy)
@@ -3218,7 +3218,10 @@ asan_expand_mark_ifn (gimple_stmt_iterat
   /* Generate direct emission if size_in_bytes is small.  */
   if (size_in_bytes <= ASAN_PARAM_USE_AFTER_SCOPE_DIRECT_EMISSION_THRESHOLD)
     {
-      unsigned HOST_WIDE_INT shadow_size = shadow_mem_size (size_in_bytes);
+      const unsigned HOST_WIDE_INT shadow_size
+	= shadow_mem_size (size_in_bytes);
+      const unsigned int shadow_align
+	= (get_pointer_alignment (base) / BITS_PER_UNIT) >> ASAN_SHADOW_SHIFT;
 
       tree shadow = build_shadow_mem_access (iter, loc, base_addr,
 					     shadow_ptr_types[0], true);
@@ -3226,9 +3229,11 @@ asan_expand_mark_ifn (gimple_stmt_iterat
       for (unsigned HOST_WIDE_INT offset = 0; offset < shadow_size;)
 	{
 	  unsigned size = 1;
-	  if (shadow_size - offset >= 4)
+	  if (shadow_size - offset >= 4
+	      && (!STRICT_ALIGNMENT || shadow_align >= 4))
 	    size = 4;
-	  else if (shadow_size - offset >= 2)
+	  else if (shadow_size - offset >= 2
+		   && (!STRICT_ALIGNMENT || shadow_align >= 2))
 	    size = 2;
 
 	  unsigned HOST_WIDE_INT last_chunk_size = 0;