Add a fixed_size_mode class

This patch adds a fixed_size_mode machine_mode wrapper
for modes that are known to have a fixed size.  That applies
to all current modes, but future patches will add support for
variable-sized modes.

The use of this class should be pretty restricted.  One important
use case is to hold the mode of static data, which can never be
variable-sized with current file formats.  Another is to hold
the modes of registers involved in __builtin_apply and
__builtin_result, since those interfaces don't cope well with
variable-sized data.

The class can also be useful when reinterpreting the contents of
a fixed-length bit string as a different kind of value.

2017-11-01  Richard Sandiford  <richard.sandiford@linaro.org>
	    Alan Hayward  <alan.hayward@arm.com>
	    David Sherwood  <david.sherwood@arm.com>

gcc/
	* machmode.h (fixed_size_mode): New class.
	* rtl.h (get_pool_mode): Return fixed_size_mode.
	* gengtype.c (main): Add fixed_size_mode.
	* target.def (get_raw_result_mode): Return a fixed_size_mode.
	(get_raw_arg_mode): Likewise.
	* doc/tm.texi: Regenerate.
	* targhooks.h (default_get_reg_raw_mode): Return a fixed_size_mode.
	* targhooks.c (default_get_reg_raw_mode): Likewise.
	* config/ia64/ia64.c (ia64_get_reg_raw_mode): Likewise.
	* config/mips/mips.c (mips_get_reg_raw_mode): Likewise.
	* config/msp430/msp430.c (msp430_get_raw_arg_mode): Likewise.
	(msp430_get_raw_result_mode): Likewise.
	* config/avr/avr-protos.h (regmask): Use as_a <fixed_side_mode>
	* dbxout.c (dbxout_parms): Require fixed-size modes.
	* expr.c (copy_blkmode_from_reg, copy_blkmode_to_reg): Likewise.
	* gimple-ssa-store-merging.c (encode_tree_to_bitpos): Likewise.
	* omp-low.c (lower_oacc_reductions): Likewise.
	* simplify-rtx.c (simplify_immed_subreg): Take fixed_size_modes.
	(simplify_subreg): Update accordingly.
	* varasm.c (constant_descriptor_rtx::mode): Change to fixed_size_mode.
	(force_const_mem): Update accordingly.  Return NULL_RTX for modes
	that aren't fixed-size.
	(get_pool_mode): Return a fixed_size_mode.
	(output_constant_pool_2): Take a fixed_size_mode.

Co-Authored-By: Alan Hayward <alan.hayward@arm.com>
Co-Authored-By: David Sherwood <david.sherwood@arm.com>

From-SVN: r254300

1 files changed, 9 insertions, 6 deletions

diff --git a/gcc/expr.c b/gcc/expr.c
index cb294bb..edcd7e8 100644
--- a/gcc/expr.c
+++ b/gcc/expr.c
@@ -2628,9 +2628,10 @@ copy_blkmode_from_reg (rtx target, rtx srcreg, tree type)
   rtx src = NULL, dst = NULL;
   unsigned HOST_WIDE_INT bitsize = MIN (TYPE_ALIGN (type), BITS_PER_WORD);
   unsigned HOST_WIDE_INT bitpos, xbitpos, padding_correction = 0;
-  machine_mode mode = GET_MODE (srcreg);
-  machine_mode tmode = GET_MODE (target);
-  machine_mode copy_mode;
+  /* No current ABI uses variable-sized modes to pass a BLKmnode type.  */
+  fixed_size_mode mode = as_a <fixed_size_mode> (GET_MODE (srcreg));
+  fixed_size_mode tmode = as_a <fixed_size_mode> (GET_MODE (target));
+  fixed_size_mode copy_mode;
 
   /* BLKmode registers created in the back-end shouldn't have survived.  */
   gcc_assert (mode != BLKmode);
@@ -2728,19 +2729,21 @@ copy_blkmode_from_reg (rtx target, rtx srcreg, tree type)
     }
 }
 
-/* Copy BLKmode value SRC into a register of mode MODE.  Return the
+/* Copy BLKmode value SRC into a register of mode MODE_IN.  Return the
    register if it contains any data, otherwise return null.
 
    This is used on targets that return BLKmode values in registers.  */
 
 rtx
-copy_blkmode_to_reg (machine_mode mode, tree src)
+copy_blkmode_to_reg (machine_mode mode_in, tree src)
 {
   int i, n_regs;
   unsigned HOST_WIDE_INT bitpos, xbitpos, padding_correction = 0, bytes;
   unsigned int bitsize;
   rtx *dst_words, dst, x, src_word = NULL_RTX, dst_word = NULL_RTX;
-  machine_mode dst_mode;
+  /* No current ABI uses variable-sized modes to pass a BLKmnode type.  */
+  fixed_size_mode mode = as_a <fixed_size_mode> (mode_in);
+  fixed_size_mode dst_mode;
 
   gcc_assert (TYPE_MODE (TREE_TYPE (src)) == BLKmode);