[Trivial] tree-sra.c: A few comment fixes/additions.

    
	* tree-sra.c (scalarizable_type_p): Comment variable-length arrays.
	(completely_scalarize): Comment zero-length arrays.
	(get_access_replacement): Correct comment re. precondition.

From-SVN: r229577

gcc/ChangeLog

+2015-10-30  Alan Lawrence  <alan.lawrence@arm.com>
+
+	* tree-sra.c (scalarizable_type_p): Comment variable-length arrays.
+	(completely_scalarize): Comment zero-length arrays.
+	(get_access_replacement): Correct comment re. precondition.
+
 2015-10-30  Venkataramanan Kumar  <venkataramanan.kumar@amd.com>
 
 	* config/i386/i386.c (get_builtin_code_for_version): Set priority

gcc/tree-sra.c

@@ -956,6 +956,7 @@ scalarizable_type_p (tree type)
 	;
       else if ((tree_to_shwi (TYPE_SIZE (type)) <= 0)
 	       || !tree_fits_shwi_p (TYPE_MAX_VALUE (TYPE_DOMAIN (type))))
+	/* Variable-length array, do not allow scalarization.  */
 	return false;
 
       tree elem = TREE_TYPE (type);
@@ -1005,6 +1006,7 @@ completely_scalarize (tree base, tree decl_type, HOST_WIDE_INT offset, tree ref)
 	tree minidx = TYPE_MIN_VALUE (TYPE_DOMAIN (decl_type));
 	gcc_assert (TREE_CODE (minidx) == INTEGER_CST);
 	tree maxidx = TYPE_MAX_VALUE (TYPE_DOMAIN (decl_type));
+	/* Skip (some) zero-length arrays; others have MAXIDX == MINIDX - 1.  */
 	if (maxidx)
 	  {
 	    gcc_assert (TREE_CODE (maxidx) == INTEGER_CST);
@@ -2146,7 +2148,7 @@ create_access_replacement (struct access *access)
   return repl;
 }
 
-/* Return ACCESS scalar replacement, create it if it does not exist yet.  */
+/* Return ACCESS scalar replacement, which must exist.  */
 
 static inline tree
 get_access_replacement (struct access *access)