-/* Extract a bit field from a memory by forcing the alignment of the
- memory. This efficient only if the field spans at least 4 boundaries.
-
- OP0 is the MEM.
- BITSIZE is the field width; BITPOS is the position of the first bit.
- UNSIGNEDP is true if the result should be zero-extended. */
-
-static rtx
-extract_force_align_mem_bit_field (rtx op0, unsigned HOST_WIDE_INT bitsize,
- unsigned HOST_WIDE_INT bitpos,
- int unsignedp)
-{
- enum machine_mode mode, dmode;
- unsigned int m_bitsize, m_size;
- unsigned int sign_shift_up, sign_shift_dn;
- rtx base, a1, a2, v1, v2, comb, shift, result, start;
-
- /* Choose a mode that will fit BITSIZE. */
- mode = smallest_mode_for_size (bitsize, MODE_INT);
- m_size = GET_MODE_SIZE (mode);
- m_bitsize = GET_MODE_BITSIZE (mode);
-
- /* Choose a mode twice as wide. Fail if no such mode exists. */
- dmode = mode_for_size (m_bitsize * 2, MODE_INT, false);
- if (dmode == BLKmode)
- return NULL;
-
- do_pending_stack_adjust ();
- start = get_last_insn ();
-
- /* At the end, we'll need an additional shift to deal with sign/zero
- extension. By default this will be a left+right shift of the
- appropriate size. But we may be able to eliminate one of them. */
- sign_shift_up = sign_shift_dn = m_bitsize - bitsize;
-
- if (STRICT_ALIGNMENT)
- {
- base = plus_constant (XEXP (op0, 0), bitpos / BITS_PER_UNIT);
- bitpos %= BITS_PER_UNIT;
-
- /* We load two values to be concatenate. There's an edge condition
- that bears notice -- an aligned value at the end of a page can
- only load one value lest we segfault. So the two values we load
- are at "base & -size" and "(base + size - 1) & -size". If base
- is unaligned, the addresses will be aligned and sequential; if
- base is aligned, the addresses will both be equal to base. */
-
- a1 = expand_simple_binop (Pmode, AND, force_operand (base, NULL),
- GEN_INT (-(HOST_WIDE_INT)m_size),
- NULL, true, OPTAB_LIB_WIDEN);
- mark_reg_pointer (a1, m_bitsize);
- v1 = gen_rtx_MEM (mode, a1);
- set_mem_align (v1, m_bitsize);
- v1 = force_reg (mode, validize_mem (v1));
-
- a2 = plus_constant (base, GET_MODE_SIZE (mode) - 1);
- a2 = expand_simple_binop (Pmode, AND, force_operand (a2, NULL),
- GEN_INT (-(HOST_WIDE_INT)m_size),
- NULL, true, OPTAB_LIB_WIDEN);
- v2 = gen_rtx_MEM (mode, a2);
- set_mem_align (v2, m_bitsize);
- v2 = force_reg (mode, validize_mem (v2));
-
- /* Combine these two values into a double-word value. */
- if (m_bitsize == BITS_PER_WORD)
- {
- comb = gen_reg_rtx (dmode);
- emit_insn (gen_rtx_CLOBBER (VOIDmode, comb));
- emit_move_insn (gen_rtx_SUBREG (mode, comb, 0), v1);
- emit_move_insn (gen_rtx_SUBREG (mode, comb, m_size), v2);
- }
- else
- {
- if (BYTES_BIG_ENDIAN)
- comb = v1, v1 = v2, v2 = comb;
- v1 = convert_modes (dmode, mode, v1, true);
- if (v1 == NULL)
- goto fail;
- v2 = convert_modes (dmode, mode, v2, true);
- v2 = expand_simple_binop (dmode, ASHIFT, v2, GEN_INT (m_bitsize),
- NULL, true, OPTAB_LIB_WIDEN);
- if (v2 == NULL)
- goto fail;
- comb = expand_simple_binop (dmode, IOR, v1, v2, NULL,
- true, OPTAB_LIB_WIDEN);
- if (comb == NULL)
- goto fail;
- }
-
- shift = expand_simple_binop (Pmode, AND, base, GEN_INT (m_size - 1),
- NULL, true, OPTAB_LIB_WIDEN);
- shift = expand_mult (Pmode, shift, GEN_INT (BITS_PER_UNIT), NULL, 1);
-
- if (bitpos != 0)
- {
- if (sign_shift_up <= bitpos)
- bitpos -= sign_shift_up, sign_shift_up = 0;
- shift = expand_simple_binop (Pmode, PLUS, shift, GEN_INT (bitpos),
- NULL, true, OPTAB_LIB_WIDEN);
- }
- }
- else
- {
- unsigned HOST_WIDE_INT offset = bitpos / BITS_PER_UNIT;
- bitpos %= BITS_PER_UNIT;
-
- /* When strict alignment is not required, we can just load directly
- from memory without masking. If the remaining BITPOS offset is
- small enough, we may be able to do all operations in MODE as
- opposed to DMODE. */
- if (bitpos + bitsize <= m_bitsize)
- dmode = mode;
- comb = adjust_address (op0, dmode, offset);
-
- if (sign_shift_up <= bitpos)
- bitpos -= sign_shift_up, sign_shift_up = 0;
- shift = GEN_INT (bitpos);
- }
-
- /* Shift down the double-word such that the requested value is at bit 0. */
- if (shift != const0_rtx)
- comb = expand_simple_binop (dmode, unsignedp ? LSHIFTRT : ASHIFTRT,
- comb, shift, NULL, unsignedp, OPTAB_LIB_WIDEN);
- if (comb == NULL)
- goto fail;
-
- /* If the field exactly matches MODE, then all we need to do is return the
- lowpart. Otherwise, shift to get the sign bits set properly. */
- result = force_reg (mode, gen_lowpart (mode, comb));
-
- if (sign_shift_up)
- result = expand_simple_binop (mode, ASHIFT, result,
- GEN_INT (sign_shift_up),
- NULL_RTX, 0, OPTAB_LIB_WIDEN);
- if (sign_shift_dn)
- result = expand_simple_binop (mode, unsignedp ? LSHIFTRT : ASHIFTRT,
- result, GEN_INT (sign_shift_dn),
- NULL_RTX, 0, OPTAB_LIB_WIDEN);
-
- return result;
-
- fail:
- delete_insns_since (start);
- return NULL;
-}
-
OSDN Git Service
