[PATCH][2/n] alias.c TLC

[PATCH][2/n] alias.c TLC

[Richard Guenther]

This makes ao_ref_from_mem less conservative if either MEM_OFFSET or
MEM_SIZE is not set.  From other alias.c code and 
set_mem_attributes_minus_bitpos one has to conclude that MEM_EXPR
is always conservatively correct (it only can cover a larger memory
area) and the MEM_OFFSET / MEM_SIZE pair can refine it.  Thus,
we can make ao_ref_from_mem less conservative when, for example,
faced with variable array accesses which set_mem_attributes_minus_bitpos
ends up representing with an unknown MEM_OFFSET.

Bootstrap and regtest running on x86_64-unknown-linux-gnu.

Richard.

2012-06-11  Richard Guenther  <rguenther@suse.de>

	* emit-rtl.c (set_mem_attributes_minus_bitpos): Remove dead code.
	* alias.c (ao_ref_from_mem): MEM_EXPR is conservative, MEM_OFFSET
	and MEM_SIZE only refines it.  Reflect that and be less conservative
	if either of the latter is not known.

Index: gcc/emit-rtl.c
===================================================================
*** gcc/emit-rtl.c	(revision 188384)
--- gcc/emit-rtl.c	(working copy)
*************** set_mem_attributes_minus_bitpos (rtx ref
*** 1838,1852 ****
  	      /* ??? Any reason the field size would be different than
  		 the size we got from the type?  */
  	    }
- 
- 	  /* If this is an indirect reference, record it.  */
- 	  else if (TREE_CODE (t) == MEM_REF)
- 	    {
- 	      attrs.expr = t;
- 	      attrs.offset_known_p = true;
- 	      attrs.offset = 0;
- 	      apply_bitpos = bitpos;
- 	    }
  	}
  
        /* If this is an indirect reference, record it.  */
--- 1838,1843 ----
Index: gcc/alias.c
===================================================================
*** gcc/alias.c	(revision 188384)
--- gcc/alias.c	(working copy)
*************** ao_ref_from_mem (ao_ref *ref, const_rtx
*** 326,342 ****
  
    ref->ref_alias_set = MEM_ALIAS_SET (mem);
  
!   /* If MEM_OFFSET or MEM_SIZE are unknown we have to punt.
!      Keep points-to related information though.  */
    if (!MEM_OFFSET_KNOWN_P (mem)
        || !MEM_SIZE_KNOWN_P (mem))
!     {
!       ref->ref = NULL_TREE;
!       ref->offset = 0;
!       ref->size = -1;
!       ref->max_size = -1;
!       return true;
!     }
  
    /* If the base decl is a parameter we can have negative MEM_OFFSET in
       case of promoted subregs on bigendian targets.  Trust the MEM_EXPR
--- 326,336 ----
  
    ref->ref_alias_set = MEM_ALIAS_SET (mem);
  
!   /* If MEM_OFFSET or MEM_SIZE are unknown what we got from MEM_EXPR
!      is conservative, so trust it.  */
    if (!MEM_OFFSET_KNOWN_P (mem)
        || !MEM_SIZE_KNOWN_P (mem))
!     return true;
  
    /* If the base decl is a parameter we can have negative MEM_OFFSET in
       case of promoted subregs on bigendian targets.  Trust the MEM_EXPR
*************** ao_ref_from_mem (ao_ref *ref, const_rtx
*** 345,350 ****
--- 339,347 ----
        && (MEM_SIZE (mem) + MEM_OFFSET (mem)) * BITS_PER_UNIT == ref->size)
      return true;
  
+   /* Otherwise continue and refine size and offset we got from analyzing
+      MEM_EXPR by using MEM_SIZE and MEM_OFFSET.  */
+ 
    ref->offset += MEM_OFFSET (mem) * BITS_PER_UNIT;
    ref->size = MEM_SIZE (mem) * BITS_PER_UNIT;
  

Re: [PATCH][2/n] alias.c TLC

[H.J. Lu]

On Mon, Jun 11, 2012 at 7:32 AM, Richard Guenther <rguenther@suse.de> wrote:
>
> This makes ao_ref_from_mem less conservative if either MEM_OFFSET or
> MEM_SIZE is not set.  From other alias.c code and
> set_mem_attributes_minus_bitpos one has to conclude that MEM_EXPR
> is always conservatively correct (it only can cover a larger memory
> area) and the MEM_OFFSET / MEM_SIZE pair can refine it.  Thus,
> we can make ao_ref_from_mem less conservative when, for example,
> faced with variable array accesses which set_mem_attributes_minus_bitpos
> ends up representing with an unknown MEM_OFFSET.
>
> Bootstrap and regtest running on x86_64-unknown-linux-gnu.
>
> Richard.
>
> 2012-06-11  Richard Guenther  <rguenther@suse.de>
>
>        * emit-rtl.c (set_mem_attributes_minus_bitpos): Remove dead code.
>        * alias.c (ao_ref_from_mem): MEM_EXPR is conservative, MEM_OFFSET
>        and MEM_SIZE only refines it.  Reflect that and be less conservative
>        if either of the latter is not known.
>

This caused:

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53688

-- 
H.J.