}
}
+/* Return a new underlying object for a bitfield started with FIELD. */
+
+static tree
+start_bitfield_representative (tree field)
+{
+ tree repr = make_node (FIELD_DECL);
+ DECL_FIELD_OFFSET (repr) = DECL_FIELD_OFFSET (field);
+ /* Force the representative to begin at a BITS_PER_UNIT aligned
+ boundary - C++ may use tail-padding of a base object to
+ continue packing bits so the bitfield region does not start
+ at bit zero (see g++.dg/abi/bitfield5.C for example).
+ Unallocated bits may happen for other reasons as well,
+ for example Ada which allows explicit bit-granular structure layout. */
+ DECL_FIELD_BIT_OFFSET (repr)
+ = size_binop (BIT_AND_EXPR,
+ DECL_FIELD_BIT_OFFSET (field),
+ bitsize_int (~(BITS_PER_UNIT - 1)));
+ SET_DECL_OFFSET_ALIGN (repr, DECL_OFFSET_ALIGN (field));
+ DECL_SIZE (repr) = DECL_SIZE (field);
+ DECL_SIZE_UNIT (repr) = DECL_SIZE_UNIT (field);
+ DECL_PACKED (repr) = DECL_PACKED (field);
+ DECL_CONTEXT (repr) = DECL_CONTEXT (field);
+ return repr;
+}
+
+/* Finish up a bitfield group that was started by creating the underlying
+ object REPR with the last field in the bitfield group FIELD. */
+
+static void
+finish_bitfield_representative (tree repr, tree field)
+{
+ unsigned HOST_WIDE_INT bitsize, maxbitsize;
+ enum machine_mode mode;
+ tree nextf, size;
+
+ size = size_diffop (DECL_FIELD_OFFSET (field),
+ DECL_FIELD_OFFSET (repr));
+ gcc_assert (host_integerp (size, 1));
+ bitsize = (tree_low_cst (size, 1) * BITS_PER_UNIT
+ + tree_low_cst (DECL_FIELD_BIT_OFFSET (field), 1)
+ - tree_low_cst (DECL_FIELD_BIT_OFFSET (repr), 1)
+ + tree_low_cst (DECL_SIZE (field), 1));
+
+ /* Round up bitsize to multiples of BITS_PER_UNIT. */
+ bitsize = (bitsize + BITS_PER_UNIT - 1) & ~(BITS_PER_UNIT - 1);
+
+ /* Now nothing tells us how to pad out bitsize ... */
+ nextf = DECL_CHAIN (field);
+ while (nextf && TREE_CODE (nextf) != FIELD_DECL)
+ nextf = DECL_CHAIN (nextf);
+ if (nextf)
+ {
+ tree maxsize;
+ /* If there was an error, the field may be not laid out
+ correctly. Don't bother to do anything. */
+ if (TREE_TYPE (nextf) == error_mark_node)
+ return;
+ maxsize = size_diffop (DECL_FIELD_OFFSET (nextf),
+ DECL_FIELD_OFFSET (repr));
+ if (host_integerp (maxsize, 1))
+ {
+ maxbitsize = (tree_low_cst (maxsize, 1) * BITS_PER_UNIT
+ + tree_low_cst (DECL_FIELD_BIT_OFFSET (nextf), 1)
+ - tree_low_cst (DECL_FIELD_BIT_OFFSET (repr), 1));
+ /* If the group ends within a bitfield nextf does not need to be
+ aligned to BITS_PER_UNIT. Thus round up. */
+ maxbitsize = (maxbitsize + BITS_PER_UNIT - 1) & ~(BITS_PER_UNIT - 1);
+ }
+ else
+ maxbitsize = bitsize;
+ }
+ else
+ {
+ /* ??? If you consider that tail-padding of this struct might be
+ re-used when deriving from it we cannot really do the following
+ and thus need to set maxsize to bitsize? Also we cannot
+ generally rely on maxsize to fold to an integer constant, so
+ use bitsize as fallback for this case. */
+ tree maxsize = size_diffop (TYPE_SIZE_UNIT (DECL_CONTEXT (field)),
+ DECL_FIELD_OFFSET (repr));
+ if (host_integerp (maxsize, 1))
+ maxbitsize = (tree_low_cst (maxsize, 1) * BITS_PER_UNIT
+ - tree_low_cst (DECL_FIELD_BIT_OFFSET (repr), 1));
+ else
+ maxbitsize = bitsize;
+ }
+
+ /* Only if we don't artificially break up the representative in
+ the middle of a large bitfield with different possibly
+ overlapping representatives. And all representatives start
+ at byte offset. */
+ gcc_assert (maxbitsize % BITS_PER_UNIT == 0);
+
+ /* Find the smallest nice mode to use. */
+ for (mode = GET_CLASS_NARROWEST_MODE (MODE_INT); mode != VOIDmode;
+ mode = GET_MODE_WIDER_MODE (mode))
+ if (GET_MODE_BITSIZE (mode) >= bitsize)
+ break;
+ if (mode != VOIDmode
+ && (GET_MODE_BITSIZE (mode) > maxbitsize
+ || GET_MODE_BITSIZE (mode) > MAX_FIXED_MODE_SIZE))
+ mode = VOIDmode;
+
+ if (mode == VOIDmode)
+ {
+ /* We really want a BLKmode representative only as a last resort,
+ considering the member b in
+ struct { int a : 7; int b : 17; int c; } __attribute__((packed));
+ Otherwise we simply want to split the representative up
+ allowing for overlaps within the bitfield region as required for
+ struct { int a : 7; int b : 7;
+ int c : 10; int d; } __attribute__((packed));
+ [0, 15] HImode for a and b, [8, 23] HImode for c. */
+ DECL_SIZE (repr) = bitsize_int (bitsize);
+ DECL_SIZE_UNIT (repr) = size_int (bitsize / BITS_PER_UNIT);
+ DECL_MODE (repr) = BLKmode;
+ TREE_TYPE (repr) = build_array_type_nelts (unsigned_char_type_node,
+ bitsize / BITS_PER_UNIT);
+ }
+ else
+ {
+ unsigned HOST_WIDE_INT modesize = GET_MODE_BITSIZE (mode);
+ DECL_SIZE (repr) = bitsize_int (modesize);
+ DECL_SIZE_UNIT (repr) = size_int (modesize / BITS_PER_UNIT);
+ DECL_MODE (repr) = mode;
+ TREE_TYPE (repr) = lang_hooks.types.type_for_mode (mode, 1);
+ }
+
+ /* Remember whether the bitfield group is at the end of the
+ structure or not. */
+ DECL_CHAIN (repr) = nextf;
+}
+
+/* Compute and set FIELD_DECLs for the underlying objects we should
+ use for bitfield access for the structure laid out with RLI. */
+
+static void
+finish_bitfield_layout (record_layout_info rli)
+{
+ tree field, prev;
+ tree repr = NULL_TREE;
+
+ /* Unions would be special, for the ease of type-punning optimizations
+ we could use the underlying type as hint for the representative
+ if the bitfield would fit and the representative would not exceed
+ the union in size. */
+ if (TREE_CODE (rli->t) != RECORD_TYPE)
+ return;
+
+ for (prev = NULL_TREE, field = TYPE_FIELDS (rli->t);
+ field; field = DECL_CHAIN (field))
+ {
+ if (TREE_CODE (field) != FIELD_DECL)
+ continue;
+
+ /* In the C++ memory model, consecutive bit fields in a structure are
+ considered one memory location and updating a memory location
+ may not store into adjacent memory locations. */
+ if (!repr
+ && DECL_BIT_FIELD_TYPE (field))
+ {
+ /* Start new representative. */
+ repr = start_bitfield_representative (field);
+ }
+ else if (repr
+ && ! DECL_BIT_FIELD_TYPE (field))
+ {
+ /* Finish off new representative. */
+ finish_bitfield_representative (repr, prev);
+ repr = NULL_TREE;
+ }
+ else if (DECL_BIT_FIELD_TYPE (field))
+ {
+ gcc_assert (repr != NULL_TREE);
+
+ /* Zero-size bitfields finish off a representative and
+ do not have a representative themselves. This is
+ required by the C++ memory model. */
+ if (integer_zerop (DECL_SIZE (field)))
+ {
+ finish_bitfield_representative (repr, prev);
+ repr = NULL_TREE;
+ }
+
+ /* We assume that either DECL_FIELD_OFFSET of the representative
+ and each bitfield member is a constant or they are equal.
+ This is because we need to be able to compute the bit-offset
+ of each field relative to the representative in get_bit_range
+ during RTL expansion.
+ If these constraints are not met, simply force a new
+ representative to be generated. That will at most
+ generate worse code but still maintain correctness with
+ respect to the C++ memory model. */
+ else if (!((host_integerp (DECL_FIELD_OFFSET (repr), 1)
+ && host_integerp (DECL_FIELD_OFFSET (field), 1))
+ || operand_equal_p (DECL_FIELD_OFFSET (repr),
+ DECL_FIELD_OFFSET (field), 0)))
+ {
+ finish_bitfield_representative (repr, prev);
+ repr = start_bitfield_representative (field);
+ }
+ }
+ else
+ continue;
+
+ if (repr)
+ DECL_BIT_FIELD_REPRESENTATIVE (field) = repr;
+
+ prev = field;
+ }
+
+ if (repr)
+ finish_bitfield_representative (repr, prev);
+}
+
/* Do all of the work required to layout the type indicated by RLI,
once the fields have been laid out. This function will call `free'
for RLI, unless FREE_P is false. Passing a value other than false
/* Perform any last tweaks to the TYPE_SIZE, etc. */
finalize_type_size (rli->t);
+ /* Compute bitfield representatives. */
+ finish_bitfield_layout (rli);
+
/* Propagate TYPE_PACKED to variants. With C++ templates,
handle_packed_attribute is too early to do this. */
for (variant = TYPE_NEXT_VARIANT (rli->t); variant;
TYPE_SIZE (type) = int_const_binop (MULT_EXPR, TYPE_SIZE (innertype),
bitsize_int (nunits));
- /* Always naturally align vectors. This prevents ABI changes
- depending on whether or not native vector modes are supported. */
- TYPE_ALIGN (type) = tree_low_cst (TYPE_SIZE (type), 0);
+ /* For vector types, we do not default to the mode's alignment.
+ Instead, query a target hook, defaulting to natural alignment.
+ This prevents ABI changes depending on whether or not native
+ vector modes are supported. */
+ TYPE_ALIGN (type) = targetm.vector_alignment (type);
+
+ /* However, if the underlying mode requires a bigger alignment than
+ what the target hook provides, we cannot use the mode. For now,
+ simply reject that case. */
+ gcc_assert (TYPE_ALIGN (type)
+ >= GET_MODE_ALIGNMENT (TYPE_MODE (type)));
break;
}
if (!bitregion_end)
maxbits = MAX_FIXED_MODE_SIZE;
else
- maxbits = (bitregion_end - bitregion_start) % align + 1;
+ maxbits = bitregion_end - bitregion_start + 1;
/* Find the narrowest integer mode that contains the bit field. */
for (mode = GET_CLASS_NARROWEST_MODE (MODE_INT); mode != VOIDmode;
(Though at least one Unix compiler ignores this problem:
that on the Sequent 386 machine. */
|| MIN (unit, BIGGEST_ALIGNMENT) > align
- || (largest_mode != VOIDmode && unit > GET_MODE_BITSIZE (largest_mode)))
+ || (largest_mode != VOIDmode && unit > GET_MODE_BITSIZE (largest_mode))
+ || unit > maxbits
+ || (bitregion_end
+ && bitpos - (bitpos % unit) + unit > bitregion_end + 1))
return VOIDmode;
if ((SLOW_BYTE_ACCESS && ! volatilep)
&& unit <= MIN (align, BIGGEST_ALIGNMENT)
&& unit <= maxbits
&& (largest_mode == VOIDmode
- || unit <= GET_MODE_BITSIZE (largest_mode)))
+ || unit <= GET_MODE_BITSIZE (largest_mode))
+ && (bitregion_end == 0
+ || bitpos - (bitpos % unit) + unit <= bitregion_end + 1))
wide_mode = tmode;
}
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