Re: Make nonoverlapping_component_refs work with duplicated main variants

[Richard Biener <rguenther@suse.de>]

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On Tue, 9 Jul 2019, Jan Hubicka wrote:

> Hi,
> this is updated variant I am testing.
> It documents better how function works and streamlines the checks.
> 
> OK assuming it passes the tests?
> 
> Honza
> 
> Index: tree-ssa-alias.c
> ===================================================================
> --- tree-ssa-alias.c	(revision 273193)
> +++ tree-ssa-alias.c	(working copy)
> @@ -1128,6 +1128,91 @@ aliasing_component_refs_p (tree ref1,
>    return false;
>  }
>  
> +/* FIELD1 and FIELD2 are two fields of component refs.  We assume
> +   that bases of both component refs are
> +     (*) are either equivalent or they point to different objects.

are either equivalent(*) or not overlapping

> +   We do not assume that FIELD1 and FIELD2 are of same type.

that the containers of FIELD1 and FIELD2 are of the same type?

> +
> +   Return 0 if FIELD1 and FIELD2 satisfy (*).
> +   This is the case when their offsets are the same.

Hmm, so when the offsets are the same then the bases are equivalent?
I think you want to say

     Return 0 if in case the component refs satisfy (*) we
     know FIELD1 and FIELD2 are overlapping exactly.

> +   Return 1 if FIELD1 and FIELD2 are non-overlapping.
> +
> +   Return -1 otherwise.
> +
> +   Main difference between 0 and -1 is to let
> +   nonoverlapping_component_refs_since_match_p discover the semnatically

semantically

otherwise looks good now.

Thanks,
Richard.

> +   equivalent part of the access path.
> +
> +   Note that this function is used even with -fno-strict-aliasing
> +   and makes use of no TBAA assumptions.  */
> +
> +static int
> +nonoverlapping_component_refs_p_1 (const_tree field1, const_tree field2)
> +{
> +  /* If both fields are of the same type, we could save hard work of
> +     comparing offsets.  */
> +  tree type1 = DECL_CONTEXT (field1);
> +  tree type2 = DECL_CONTEXT (field2);
> +
> +  if (DECL_BIT_FIELD_REPRESENTATIVE (field1))
> +    field1 = DECL_BIT_FIELD_REPRESENTATIVE (field1);
> +  if (DECL_BIT_FIELD_REPRESENTATIVE (field2))
> +    field2 = DECL_BIT_FIELD_REPRESENTATIVE (field1);
> +
> +  /* ??? Bitfields can overlap at RTL level so punt on them.
> +     FIXME: RTL expansion should be fixed by adjusting the access path
> +     when producing MEM_ATTRs for MEMs which are wider than 
> +     the bitfields similarly as done in set_mem_attrs_minus_bitpos.  */
> +  if (DECL_BIT_FIELD (field1) && DECL_BIT_FIELD (field2))
> +    return -1;
> +
> +  /* Assume that different FIELD_DECLs never overlap within a RECORD_TYPE.  */
> +  if (type1 == type2 && TREE_CODE (type1) == RECORD_TYPE)
> +    return field1 != field2;
> +
> +  /* In common case the offsets and bit offsets will be the same.
> +     However if frontends do not agree on the alignment, they may be
> +     different even if they actually represent same address.
> +     Try the common case first and if that fails calcualte the
> +     actual bit offset.  */
> +  if (tree_int_cst_equal (DECL_FIELD_OFFSET (field1),
> +			  DECL_FIELD_OFFSET (field2))
> +      && tree_int_cst_equal (DECL_FIELD_BIT_OFFSET (field1),
> +			     DECL_FIELD_BIT_OFFSET (field2)))
> +    return 0;
> +
> +  /* Note that it may be possible to use component_ref_field_offset
> +     which would provide offsets as trees. However constructing and folding
> +     trees is expensive and does not seem to be worth the compile time
> +     cost.  */
> +
> +  poly_uint64 offset1, offset2;
> +  poly_uint64 bit_offset1, bit_offset2;
> +
> +  if (poly_int_tree_p (DECL_FIELD_OFFSET (field1), &offset1)
> +      && poly_int_tree_p (DECL_FIELD_OFFSET (field2), &offset2)
> +      && poly_int_tree_p (DECL_FIELD_BIT_OFFSET (field1), &bit_offset1)
> +      && poly_int_tree_p (DECL_FIELD_BIT_OFFSET (field2), &bit_offset2))
> +    {
> +      offset1 = (offset1 << LOG2_BITS_PER_UNIT) + bit_offset1;
> +      offset2 = (offset2 << LOG2_BITS_PER_UNIT) + bit_offset2;
> +
> +      if (known_eq (offset1, offset2))
> +	return 0;
> +
> +      poly_uint64 size1, size2;
> +
> +      if (poly_int_tree_p (DECL_SIZE (field1), &size1)
> +	  && poly_int_tree_p (DECL_SIZE (field2), &size2)
> +	  && !ranges_maybe_overlap_p (offset1, size1, offset2, size2))
> +	return 1;
> +    }
> +  /* Resort to slower overlap checking by looking for matching types in
> +     the middle of access path.  */
> +  return -1;
> +}
> +
>  /* Try to disambiguate REF1 and REF2 under the assumption that MATCH1 and
>     MATCH2 either point to the same address or are disjoint.
>     MATCH1 and MATCH2 are assumed to be ref in the access path of REF1 and REF2
> @@ -1224,6 +1309,7 @@ nonoverlapping_component_refs_since_matc
>       case the return value will precisely be false.  */
>    while (true)
>      {
> +      bool seen_noncomponent_ref_p = false;
>        do
>  	{
>  	  if (component_refs1.is_empty ())
> @@ -1233,6 +1319,8 @@ nonoverlapping_component_refs_since_matc
>  	      return 0;
>  	    }
>  	  ref1 = component_refs1.pop ();
> +	  if (TREE_CODE (ref1) != COMPONENT_REF)
> +	    seen_noncomponent_ref_p = true;
>  	}
>        while (!RECORD_OR_UNION_TYPE_P (TREE_TYPE (TREE_OPERAND (ref1, 0))));
>  
> @@ -1245,17 +1333,15 @@ nonoverlapping_component_refs_since_matc
>  	      return 0;
>  	    }
>  	  ref2 = component_refs2.pop ();
> +	  if (TREE_CODE (ref2) != COMPONENT_REF)
> +	    seen_noncomponent_ref_p = true;
>  	}
>        while (!RECORD_OR_UNION_TYPE_P (TREE_TYPE (TREE_OPERAND (ref2, 0))));
>  
> -      /* Beware of BIT_FIELD_REF.  */
> -      if (TREE_CODE (ref1) != COMPONENT_REF
> -	  || TREE_CODE (ref2) != COMPONENT_REF)
> -	{
> -	  ++alias_stats
> -		.nonoverlapping_component_refs_since_match_p_may_alias;
> -	  return -1;
> -	}
> +      /* BIT_FIELD_REF and VIEW_CONVERT_EXPR are taken off the vectors
> +	 earlier.  */
> +      gcc_checking_assert (TREE_CODE (ref1) == COMPONENT_REF
> +			   && TREE_CODE (ref2) == COMPONENT_REF);
>  
>        tree field1 = TREE_OPERAND (ref1, 1);
>        tree field2 = TREE_OPERAND (ref2, 1);
> @@ -1266,33 +1352,27 @@ nonoverlapping_component_refs_since_matc
>        tree type1 = DECL_CONTEXT (field1);
>        tree type2 = DECL_CONTEXT (field2);
>  
> -      /* We cannot disambiguate fields in a union or qualified union.  */
> -      if (type1 != type2 || TREE_CODE (type1) != RECORD_TYPE)
> +      /* If we skipped array refs on type of different sizes, we can
> +	 no longer be sure that there are not partial overlaps.  */
> +      if (seen_noncomponent_ref_p
> +	  && !operand_equal_p (TYPE_SIZE (type1), TYPE_SIZE (type2), 0))
>  	{
> -	  ++alias_stats.nonoverlapping_component_refs_since_match_p_may_alias;
> +	  ++alias_stats
> +	    .nonoverlapping_component_refs_since_match_p_may_alias;
>  	  return -1;
>  	}
>  
> -      if (field1 != field2)
> +      int cmp = nonoverlapping_component_refs_p_1 (field1, field2);
> +      if (cmp == -1)
>  	{
> -	  /* A field and its representative need to be considered the
> -	     same.  */
> -	  if (DECL_BIT_FIELD_REPRESENTATIVE (field1) == field2
> -	      || DECL_BIT_FIELD_REPRESENTATIVE (field2) == field1)
> -	    {
> -	      ++alias_stats
> -		.nonoverlapping_component_refs_since_match_p_must_overlap;
> -	      return 0;
> -	    }
> -	  /* Different fields of the same record type cannot overlap.
> -	     ??? Bitfields can overlap at RTL level so punt on them.  */
> -	  if (DECL_BIT_FIELD (field1) && DECL_BIT_FIELD (field2))
> -	    {
> -	      ++alias_stats
> -		.nonoverlapping_component_refs_since_match_p_must_overlap;
> -	      return 0;
> -	    }
> -	  ++alias_stats.nonoverlapping_component_refs_since_match_p_no_alias;
> +	  ++alias_stats
> +	    .nonoverlapping_component_refs_since_match_p_may_alias;
> +	  return -1;
> +	}
> +      else if (cmp == 1)
> +	{
> +	  ++alias_stats
> +	    .nonoverlapping_component_refs_since_match_p_no_alias;
>  	  return 1;
>  	}
>      }
> @@ -1301,6 +1381,24 @@ nonoverlapping_component_refs_since_matc
>    return 0;
>  }
>  
> +/* Return TYPE_UID which can be used to match record types we consider
> +   same for TBAA purposes.  */
> +
> +static inline int
> +ncr_type_uid (const_tree field)
> +{
> +  /* ??? We cannot simply use the type of operand #0 of the refs here
> +     as the Fortran compiler smuggles type punning into COMPONENT_REFs
> +     for common blocks instead of using unions like everyone else.  */
> +  tree type = DECL_FIELD_CONTEXT (field);
> +  /* With LTO types considered same_type_for_tbaa_p 
> +     from different translation unit may not have same
> +     main variant.  They however have same TYPE_CANONICAL.  */
> +  if (TYPE_CANONICAL (type))
> +    return TYPE_UID (TYPE_CANONICAL (type));
> +  return TYPE_UID (type);
> +}
> +
>  /* qsort compare function to sort FIELD_DECLs after their
>     DECL_FIELD_CONTEXT TYPE_UID.  */
>  
> @@ -1309,8 +1407,9 @@ ncr_compar (const void *field1_, const v
>  {
>    const_tree field1 = *(const_tree *) const_cast <void *>(field1_);
>    const_tree field2 = *(const_tree *) const_cast <void *>(field2_);
> -  unsigned int uid1 = TYPE_UID (DECL_FIELD_CONTEXT (field1));
> -  unsigned int uid2 = TYPE_UID (DECL_FIELD_CONTEXT (field2));
> +  unsigned int uid1 = ncr_type_uid (field1);
> +  unsigned int uid2 = ncr_type_uid (field2);
> +
>    if (uid1 < uid2)
>      return -1;
>    else if (uid1 > uid2)
> @@ -1377,10 +1476,9 @@ nonoverlapping_component_refs_p (const_t
>    if (fieldsx.length () == 1
>        && fieldsy.length () == 1)
>     {
> -     if ((DECL_FIELD_CONTEXT (fieldsx[0])
> -         == DECL_FIELD_CONTEXT (fieldsy[0]))
> -        && fieldsx[0] != fieldsy[0]
> -        && !(DECL_BIT_FIELD (fieldsx[0]) && DECL_BIT_FIELD (fieldsy[0])))
> +     if (same_type_for_tbaa (DECL_FIELD_CONTEXT (fieldsx[0]),
> +			     DECL_FIELD_CONTEXT (fieldsy[0])) == 1
> +	 && nonoverlapping_component_refs_p_1 (fieldsx[0], fieldsy[0]) == 1)
>        {
>           ++alias_stats.nonoverlapping_component_refs_p_no_alias;
>           return true;
> @@ -1413,31 +1511,18 @@ nonoverlapping_component_refs_p (const_t
>      {
>        const_tree fieldx = fieldsx[i];
>        const_tree fieldy = fieldsy[j];
> -      tree typex = DECL_FIELD_CONTEXT (fieldx);
> -      tree typey = DECL_FIELD_CONTEXT (fieldy);
> -      if (typex == typey)
> -	{
> -	  /* We're left with accessing different fields of a structure,
> -	     no possible overlap.  */
> -	  if (fieldx != fieldy)
> -	    {
> -	      /* A field and its representative need to be considered the
> -		 same.  */
> -	      if (DECL_BIT_FIELD_REPRESENTATIVE (fieldx) == fieldy
> -		  || DECL_BIT_FIELD_REPRESENTATIVE (fieldy) == fieldx)
> -		;
> -	      /* Different fields of the same record type cannot overlap.
> -		 ??? Bitfields can overlap at RTL level so punt on them.  */
> -	      else if (DECL_BIT_FIELD (fieldx) && DECL_BIT_FIELD (fieldy))
> -		;
> -	      else
> -		{
> -		  ++alias_stats.nonoverlapping_component_refs_p_no_alias;
> -		  return true;
> -		}
> -	    }
> +
> +      /* We're left with accessing different fields of a structure,
> +	 no possible overlap.  */
> +      if (same_type_for_tbaa (DECL_FIELD_CONTEXT (fieldx),
> +			      DECL_FIELD_CONTEXT (fieldy)) == 1
> +	  && nonoverlapping_component_refs_p_1 (fieldx, fieldy) == 1)
> +	{
> +	  ++alias_stats.nonoverlapping_component_refs_p_no_alias;
> +	  return true;
>  	}
> -      if (TYPE_UID (typex) < TYPE_UID (typey))
> +
> +      if (ncr_type_uid (fieldx) < ncr_type_uid (fieldy))
>  	{
>  	  i++;
>  	  if (i == fieldsx.length ())
> 

-- 
Richard Biener <rguenther@suse.de>
SUSE Linux GmbH, Maxfeldstrasse 5, 90409 Nuernberg, Germany;
GF: Felix Imendörffer, Mary Higgins, Sri Rasiah; HRB 21284 (AG NÌrnberg)