[PATCH][C] Do not expand array-refs via pointer arithmetic

[PATCH][C] Do not expand array-refs via pointer arithmetic

[Richard Guenther]

This patch adjusts the C frontend to retain array-refs in
address-taking operations instead of expanding them via
pointer arithmetic.  As seen in PR48571 we can't re-construct
array-refs in the middle-end, thus we should keep information
as specified by the source level.

For

int a[10];
int *foo (int i)
{
  return &a[i];
}
int *bar (int i)
{
  return &i[a];
}

this will now emit

  return &a[i];

instead of

  return (int *) &a + (long unsigned int) ((long unsigned int) i * 4);

which is also shorter.

Bootstrapped and tested on x86_64-unknown-linux-gnu.

Ok for trunk?

Thanks,
Richard.

2011-04-14  Richard Guenther  <rguenther@suse.de>

	* c-typeck.c (build_unary_op): Do not expand array-refs via
	pointer arithmetic.  Only adjust qualifiers for function types.

Index: gcc/c-typeck.c
===================================================================
--- gcc/c-typeck.c	(revision 172319)
+++ gcc/c-typeck.c	(working copy)
@@ -3737,12 +3737,6 @@ build_unary_op (location_t location,
 	  tree op0 = TREE_OPERAND (arg, 0);
 	  if (!c_mark_addressable (op0))
 	    return error_mark_node;
-	  return build_binary_op (location, PLUS_EXPR,
-				  (TREE_CODE (TREE_TYPE (op0)) == ARRAY_TYPE
-				   ? array_to_pointer_conversion (location,
-								  op0)
-				   : op0),
-				  TREE_OPERAND (arg, 1), 1);
 	}
 
       /* Anything not already handled and not a true memory reference
@@ -3769,10 +3763,11 @@ build_unary_op (location_t location,
       argtype = TREE_TYPE (arg);
 
       /* If the lvalue is const or volatile, merge that into the type
-	 to which the address will point.  This should only be needed
+	 to which the address will point.  This is only needed
 	 for function types.  */
       if ((DECL_P (arg) || REFERENCE_CLASS_P (arg))
-	  && (TREE_READONLY (arg) || TREE_THIS_VOLATILE (arg)))
+	  && (TREE_READONLY (arg) || TREE_THIS_VOLATILE (arg))
+	  && TREE_CODE (argtype) == FUNCTION_TYPE)
 	{
 	  int orig_quals = TYPE_QUALS (strip_array_types (argtype));
 	  int quals = orig_quals;
@@ -3782,9 +3777,6 @@ build_unary_op (location_t location,
 	  if (TREE_THIS_VOLATILE (arg))
 	    quals |= TYPE_QUAL_VOLATILE;
 
-	  gcc_assert (quals == orig_quals
-		      || TREE_CODE (argtype) == FUNCTION_TYPE);
-
 	  argtype = c_build_qualified_type (argtype, quals);
 	}
 

Re: [PATCH][C] Do not expand array-refs via pointer arithmetic

[Joseph S. Myers]

On Thu, 14 Apr 2011, Richard Guenther wrote:

> 2011-04-14  Richard Guenther  <rguenther@suse.de>
> 
> 	* c-typeck.c (build_unary_op): Do not expand array-refs via
> 	pointer arithmetic.  Only adjust qualifiers for function types.

OK.

-- 
Joseph S. Myers
joseph@codesourcery.com