Fix vectorizer conditions on updating alignment

[Jan Hubicka <hubicka at ucw dot cz>]

Hi,
while updating vect_can_force_dr_alignment_p for section API I noticed the
predicate is bit confused about when it can update the alignment.

We need to check that decl_binds_to_current_def_p and in case we compile
a partition also that the symbol is not homed in other partition.
Previous code was wrong i.e. for COMDATs, weaks or -fpic.

Also when having an alias, only way to promote the alignment is to bump
up alignment of target.

On the other hand comment about DECL_IN_CONSTANT_POOL seems confused - we have
no sharing across partitions. I assume it was old hack and removed it.

I also see no reason for disregarding DECL_PRESERVE - we only update
alignment that should not disturb whatever magic user does. But I kept
it.

We probably should separate the logic into symtab predicate - it just checks if
we can change definition of variable to meet our needs. I can do that
incrementally.

Bootstrapped/regtested x86_64-linux, comitted.

Honza

	* tree-vect-data-refs.c (vect_can_force_dr_alignment_p): Reorg
	to use symtab and decl_binds_to_current_def_p
	* tree-vectorizer.c (increase_alignment): Increase alignment
	of alias target, too.
Index: tree-vect-data-refs.c
===================================================================
--- tree-vect-data-refs.c	(revision 211489)
+++ tree-vect-data-refs.c	(working copy)
@@ -58,6 +58,7 @@ along with GCC; see the file COPYING3.
 #include "expr.h"
 #include "optabs.h"
 #include "builtins.h"
+#include "varasm.h"
 
 /* Return true if load- or store-lanes optab OPTAB is implemented for
    COUNT vectors of type VECTYPE.  NAME is the name of OPTAB.  */
@@ -5316,19 +5317,26 @@ vect_can_force_dr_alignment_p (const_tre
   if (TREE_CODE (decl) != VAR_DECL)
     return false;
 
-  /* We cannot change alignment of common or external symbols as another
-     translation unit may contain a definition with lower alignment.  
-     The rules of common symbol linking mean that the definition
-     will override the common symbol.  The same is true for constant
-     pool entries which may be shared and are not properly merged
-     by LTO.  */
-  if (DECL_EXTERNAL (decl)
-      || DECL_COMMON (decl)
-      || DECL_IN_CONSTANT_POOL (decl))
-    return false;
+  gcc_assert (!TREE_ASM_WRITTEN (decl));
 
-  if (TREE_ASM_WRITTEN (decl))
-    return false;
+  if (TREE_PUBLIC (decl) || DECL_EXTERNAL (decl))
+    {
+      symtab_node *snode;
+
+      /* We cannot change alignment of symbols that may bind to symbols
+	 in other translation unit that may contain a definition with lower
+	 alignment.  */
+      if (!decl_binds_to_current_def_p (decl))
+	return false;
+
+      /* When compiling partition, be sure the symbol is not output by other
+	 partition.  */
+      snode = symtab_get_node (decl);
+      if (flag_ltrans
+	  && (snode->in_other_partition
+	      || symtab_get_symbol_partitioning_class (snode) == SYMBOL_DUPLICATE))
+	return false;
+    }
 
   /* Do not override the alignment as specified by the ABI when the used
      attribute is set.  */
@@ -5343,6 +5351,18 @@ vect_can_force_dr_alignment_p (const_tre
       && !symtab_get_node (decl)->implicit_section)
     return false;
 
+  /* If symbol is an alias, we need to check that target is OK.  */
+  if (TREE_STATIC (decl))
+    {
+      tree target = symtab_alias_ultimate_target (symtab_get_node (decl))->decl;
+      if (target != decl)
+	{
+	  if (DECL_PRESERVE_P (target))
+	    return false;
+	  decl = target;
+	}
+    }
+
   if (TREE_STATIC (decl))
     return (alignment <= MAX_OFILE_ALIGNMENT);
   else
Index: tree-vectorizer.c
===================================================================
--- tree-vectorizer.c	(revision 211488)
+++ tree-vectorizer.c	(working copy)
@@ -686,6 +686,12 @@ increase_alignment (void)
         {
           DECL_ALIGN (decl) = TYPE_ALIGN (vectype);
           DECL_USER_ALIGN (decl) = 1;
+	  if (TREE_STATIC (decl))
+	    {
+	      tree target = symtab_alias_ultimate_target (symtab_get_node (decl))->decl;
+              DECL_ALIGN (target) = TYPE_ALIGN (vectype);
+              DECL_USER_ALIGN (target) = 1;
+	    }
           dump_printf (MSG_NOTE, "Increasing alignment of decl: ");
           dump_generic_expr (MSG_NOTE, TDF_SLIM, decl);
           dump_printf (MSG_NOTE, "\n");