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, 11 insertions, 5 deletions

diff --git a/gcc/varasm.c b/gcc/varasm.c
index a139151..655324e 100644
--- a/gcc/varasm.c
+++ b/gcc/varasm.c
@@ -3566,7 +3566,7 @@ struct GTY((chain_next ("%h.next"), for_user)) constant_descriptor_rtx {
   rtx constant;
   HOST_WIDE_INT offset;
   hashval_t hash;
-  machine_mode mode;
+  fixed_size_mode mode;
   unsigned int align;
   int labelno;
   int mark;
@@ -3742,10 +3742,11 @@ simplify_subtraction (rtx x)
 }
 
 /* Given a constant rtx X, make (or find) a memory constant for its value
-   and return a MEM rtx to refer to it in memory.  */
+   and return a MEM rtx to refer to it in memory.  IN_MODE is the mode
+   of X.  */
 
 rtx
-force_const_mem (machine_mode mode, rtx x)
+force_const_mem (machine_mode in_mode, rtx x)
 {
   struct constant_descriptor_rtx *desc, tmp;
   struct rtx_constant_pool *pool;
@@ -3754,6 +3755,11 @@ force_const_mem (machine_mode mode, rtx x)
   hashval_t hash;
   unsigned int align;
   constant_descriptor_rtx **slot;
+  fixed_size_mode mode;
+
+  /* We can't force variable-sized objects to memory.  */
+  if (!is_a <fixed_size_mode> (in_mode, &mode))
+    return NULL_RTX;
 
   /* If we're not allowed to drop X into the constant pool, don't.  */
   if (targetm.cannot_force_const_mem (mode, x))
@@ -3859,7 +3865,7 @@ get_pool_constant_mark (rtx addr, bool *pmarked)
 
 /* Similar, return the mode.  */
 
-machine_mode
+fixed_size_mode
 get_pool_mode (const_rtx addr)
 {
   return SYMBOL_REF_CONSTANT (addr)->mode;
@@ -3879,7 +3885,7 @@ constant_pool_empty_p (void)
    in MODE with known alignment ALIGN.  */
 
 static void
-output_constant_pool_2 (machine_mode mode, rtx x, unsigned int align)
+output_constant_pool_2 (fixed_size_mode mode, rtx x, unsigned int align)
 {
   switch (GET_MODE_CLASS (mode))
     {