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, 14 insertions, 5 deletions

diff --git a/gcc/simplify-rtx.c b/gcc/simplify-rtx.c
index 8bee8ed..a6963ce 100644
--- a/gcc/simplify-rtx.c
+++ b/gcc/simplify-rtx.c
@@ -48,8 +48,6 @@ along with GCC; see the file COPYING3.  If not see
 static rtx neg_const_int (machine_mode, const_rtx);
 static bool plus_minus_operand_p (const_rtx);
 static rtx simplify_plus_minus (enum rtx_code, machine_mode, rtx, rtx);
-static rtx simplify_immed_subreg (machine_mode, rtx, machine_mode,
-				  unsigned int);
 static rtx simplify_associative_operation (enum rtx_code, machine_mode,
 					   rtx, rtx);
 static rtx simplify_relational_operation_1 (enum rtx_code, machine_mode,
@@ -5806,8 +5804,8 @@ simplify_ternary_operation (enum rtx_code code, machine_mode mode,
    and then repacking them again for OUTERMODE.  */
 
 static rtx
-simplify_immed_subreg (machine_mode outermode, rtx op,
-		       machine_mode innermode, unsigned int byte)
+simplify_immed_subreg (fixed_size_mode outermode, rtx op,
+		       fixed_size_mode innermode, unsigned int byte)
 {
   enum {
     value_bit = 8,
@@ -6175,7 +6173,18 @@ simplify_subreg (machine_mode outermode, rtx op,
       || CONST_DOUBLE_AS_FLOAT_P (op)
       || GET_CODE (op) == CONST_FIXED
       || GET_CODE (op) == CONST_VECTOR)
-    return simplify_immed_subreg (outermode, op, innermode, byte);
+    {
+      /* simplify_immed_subreg deconstructs OP into bytes and constructs
+	 the result from bytes, so it only works if the sizes of the modes
+	 are known at compile time.  Cases that apply to general modes
+	 should be handled here before calling simplify_immed_subreg.  */
+      fixed_size_mode fs_outermode, fs_innermode;
+      if (is_a <fixed_size_mode> (outermode, &fs_outermode)
+	  && is_a <fixed_size_mode> (innermode, &fs_innermode))
+	return simplify_immed_subreg (fs_outermode, op, fs_innermode, byte);
+
+      return NULL_RTX;
+    }
 
   /* Changing mode twice with SUBREG => just change it once,
      or not at all if changing back op starting mode.  */