[PATCH] Make CCP "complete"

[Richard Guenther]

On Thu, 14 Aug 2008, Eric Botcazou wrote:

> > 2008-08-12  Richard Guenther  <rguenther@suse.de>
> >
> > 	* tree.h (maybe_fold_offset_to_address): Declare.
> > 	* tree-ssa-ccp.c (surely_varying_stmt_p): Fix typo in last commit.
> > 	(ccp_fold): Handle pointer conversions the same as fold_stmt.
> > 	Likewise for POINTER_PLUS_EXPR.
> > 	(maybe_fold_offset_to_reference): Enable disabled code.
> > 	(maybe_fold_offset_to_address): New function.
> > 	(fold_stmt_r): Use it.
> > 	(fold_gimple_assign): Likewise.
> > 	* gimplify.c (gimplify_conversion): Use maybe_fold_offset_to_address.
> > 	(gimplify_expr): Likewise.
> 
> This breaks Ada, switch-c.adb:Scan_Front_End_Switches is miscompiled at -O0.
> 
> String slicing doesn't work anymore, testcase attached, compile with -gnatp.
> 
> We used to have in .gimple:
> 
>     D.2082 = s.P_ARRAY;
>     D.2084 = &VIEW_CONVERT_EXPR<character[D.2040:D.2042]>(*D.2082)
> [first.8 ...]{lb: D.2081 sz: 1};
>     D.2085 = (character[(long int) <PLACEHOLDER_EXPR struct 
> string___XUP>.P_BOUNDS->LB0:(long int) <PLACEHOLDER_EXPR struct 
> string___XUP>.P_BOUNDS->UB0] *) D.2084;
>     D.2080.P_ARRAY = D.2085;
> 
> Now we have:
> 
>     D.2081 = s.P_ARRAY;
>     D.2080.P_ARRAY = D.2081;

I am testing the following.

Richard.

2008-08-15  Richard Guenther  <rguenther@suse.de>

	* tree-ssa-ccp.c (maybe_fold_offset_to_reference): Do not
	strip components for unknown size accesses.

Index: gcc/tree-ssa-ccp.c
===================================================================
*** gcc/tree-ssa-ccp.c	(revision 139097)
--- gcc/tree-ssa-ccp.c	(working copy)
*************** maybe_fold_offset_to_reference (tree bas
*** 1976,1981 ****
--- 1976,1982 ----
  					     &size, &maxsize);
  	  gcc_assert (newbase);
  	  if (size == maxsize
+ 	      && size != -1
  	      && !(sub_offset & (BITS_PER_UNIT - 1)))
  	    {
  	      base = newbase;