I am reviving this patch from 2013 which properly handles
DECL_BIT_FIELD_REPRESENTATIVE appearing as FIELD_DECL operand in
a COMPONENT_REF (as I am currently reviving a patch to lower
bitfield accesses now that BIT_INSERT_EXPR is on trunk).
Bootstrapped and tested on x86_64-unknown-linux-gnu, applied to trunk.
Richard.
2016-06-28 Richard Biener <rguent...@suse.de>
* tree-ssa-alias.c (nonoverlapping_component_refs_of_decl_p):
Properly handle DECL_BIT_FIELD_REPRESENTATIVE occuring as
COMPONENT_REF operand.
(nonoverlapping_component_refs_p): Likewise.
* stor-layout.c (start_bitfield_representative): Mark
DECL_BIT_FIELD_REPRESENTATIVE as DECL_NONADDRESSABLE_P.
Index: gcc/tree-ssa-alias.c
===================================================================
*** gcc/tree-ssa-alias.c.orig 2016-06-28 10:32:02.563911183 +0200
--- gcc/tree-ssa-alias.c 2016-06-28 10:35:45.350388588 +0200
*************** nonoverlapping_component_refs_of_decl_p
*** 929,941 ****
if (type1 != type2 || TREE_CODE (type1) != RECORD_TYPE)
goto may_overlap;
- /* Different fields of the same record type cannot overlap.
- ??? Bitfields can overlap at RTL level so punt on them. */
if (field1 != field2)
{
component_refs1.release ();
component_refs2.release ();
! return !(DECL_BIT_FIELD (field1) && DECL_BIT_FIELD (field2));
}
}
--- 929,948 ----
if (type1 != type2 || TREE_CODE (type1) != RECORD_TYPE)
goto may_overlap;
if (field1 != field2)
{
component_refs1.release ();
component_refs2.release ();
! /* A field and its representative need to be considered the
! same. */
! if (DECL_BIT_FIELD_REPRESENTATIVE (field1) == field2
! || DECL_BIT_FIELD_REPRESENTATIVE (field2) == field1)
! return false;
! /* 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))
! return false;
! return true;
}
}
*************** nonoverlapping_component_refs_p (const_t
*** 1031,1039 ****
if (typex == typey)
{
/* We're left with accessing different fields of a structure,
! no possible overlap, unless they are both bitfields. */
if (fieldx != fieldy)
! return !(DECL_BIT_FIELD (fieldx) && DECL_BIT_FIELD (fieldy));
}
if (TYPE_UID (typex) < TYPE_UID (typey))
{
--- 1038,1057 ----
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)
! return false;
! /* Different fields of the same record type cannot overlap.
! ??? Bitfields can overlap at RTL level so punt on them. */
! if (DECL_BIT_FIELD (fieldx) && DECL_BIT_FIELD (fieldy))
! return false;
! return true;
! }
}
if (TYPE_UID (typex) < TYPE_UID (typey))
{
Index: gcc/stor-layout.c
===================================================================
*** gcc/stor-layout.c.orig 2016-06-28 10:32:02.563911183 +0200
--- gcc/stor-layout.c 2016-06-28 10:32:05.747946562 +0200
*************** start_bitfield_representative (tree fiel
*** 1808,1813 ****
--- 1808,1818 ----
DECL_SIZE_UNIT (repr) = DECL_SIZE_UNIT (field);
DECL_PACKED (repr) = DECL_PACKED (field);
DECL_CONTEXT (repr) = DECL_CONTEXT (field);
+ /* There are no indirect accesses to this field. If we introduce
+ some then they have to use the record alias set. This makes
+ sure to properly conflict with [indirect] accesses to addressable
+ fields of the bitfield group. */
+ DECL_NONADDRESSABLE_P (repr) = 1;
return repr;
}
