Add a partial_subreg_p predicate

This patch adds a partial_subreg_p predicate to go alongside
paradoxical_subreg_p.

Like the paradoxical_subreg_p patch, this one replaces some tests that
were based on GET_MODE_SIZE rather than GET_MODE_PRECISION.  In each
case the change should be a no-op or an improvement.

The regcprop.c patch prevents some replacements of the 82-bit RFmode
with the 80-bit XFmode on ia64.  I don't understand the target details
here particularly well, but from the way the modes are described in
ia64-modes.def, it isn't valid to assume that an XFmode can carry an
RFmode payload.  A comparison of the testsuite assembly output for one
target per CPU showed no other differences.

Some of the places changed here are tracking the widest access mode
found for a register.  The series tries to standardise on:

  if (partial_subreg_p (widest_seen, new_mode))
    widest_seen = new_mode;

rather than:

  if (paradoxical_subreg_p (new_mode, widest_seen))
    widest_seen = new_mode;

Either would have been OK.

2017-08-30  Richard Sandiford  <richard.sandiford@linaro.org>
	    Alan Hayward  <alan.hayward@arm.com>
	    David Sherwood  <david.sherwood@arm.com>

gcc/
	* rtl.h (partial_subreg_p): New function.
	* caller-save.c (save_call_clobbered_regs): Use it.
	* calls.c (expand_call): Likewise.
	* combine.c (combinable_i3pat): Likewise.
	(simplify_set): Likewise.
	(make_extraction): Likewise.
	(make_compound_operation_int): Likewise.
	(gen_lowpart_or_truncate): Likewise.
	(force_to_mode): Likewise.
	(make_field_assignment): Likewise.
	(reg_truncated_to_mode): Likewise.
	(record_truncated_value): Likewise.
	(move_deaths): Likewise.
	* cse.c (record_jump_cond): Likewise.
	(cse_insn): Likewise.
	* cselib.c (cselib_lookup_1): Likewise.
	* expmed.c (extract_bit_field_using_extv): Likewise.
	* function.c (assign_parm_setup_reg): Likewise.
	* ifcvt.c (noce_convert_multiple_sets): Likewise.
	* ira-build.c (create_insn_allocnos): Likewise.
	* lra-coalesce.c (merge_pseudos): Likewise.
	* lra-constraints.c (match_reload): Likewise.
	(simplify_operand_subreg): Likewise.
	(curr_insn_transform): Likewise.
	* lra-lives.c (process_bb_lives): Likewise.
	* lra.c (new_insn_reg): Likewise.
	(lra_substitute_pseudo): Likewise.
	* regcprop.c (mode_change_ok): Likewise.
	(maybe_mode_change): Likewise.
	(copyprop_hardreg_forward_1): Likewise.
	* reload.c (push_reload): Likewise.
	(find_reloads): Likewise.
	(find_reloads_subreg_address): Likewise.
	* reload1.c (alter_reg): Likewise.
	(eliminate_regs_1): Likewise.
	* simplify-rtx.c (simplify_unary_operation_1): Likewise.

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

From-SVN: r251536

1 files changed, 5 insertions, 5 deletions

diff --git a/gcc/regcprop.c b/gcc/regcprop.c
index 367d85a..0d4ec17 100644
--- a/gcc/regcprop.c
+++ b/gcc/regcprop.c
@@ -372,7 +372,7 @@ static bool
 mode_change_ok (machine_mode orig_mode, machine_mode new_mode,
 		unsigned int regno ATTRIBUTE_UNUSED)
 {
-  if (GET_MODE_SIZE (orig_mode) < GET_MODE_SIZE (new_mode))
+  if (partial_subreg_p (orig_mode, new_mode))
     return false;
 
 #ifdef CANNOT_CHANGE_MODE_CLASS
@@ -392,8 +392,8 @@ maybe_mode_change (machine_mode orig_mode, machine_mode copy_mode,
 		   machine_mode new_mode, unsigned int regno,
 		   unsigned int copy_regno ATTRIBUTE_UNUSED)
 {
-  if (GET_MODE_SIZE (copy_mode) < GET_MODE_SIZE (orig_mode)
-      && GET_MODE_SIZE (copy_mode) < GET_MODE_SIZE (new_mode))
+  if (partial_subreg_p (copy_mode, orig_mode)
+      && partial_subreg_p (copy_mode, new_mode))
     return NULL_RTX;
 
   /* Avoid creating multiple copies of the stack pointer.  Some ports
@@ -1076,8 +1076,8 @@ copyprop_hardreg_forward_1 (basic_block bb, struct value_data *vd)
       /* If a noop move is using narrower mode than we have recorded,
 	 we need to either remove the noop move, or kill_set_value.  */
       if (noop_p
-	  && (GET_MODE_BITSIZE (GET_MODE (SET_DEST (set)))
-	      < GET_MODE_BITSIZE (vd->e[REGNO (SET_DEST (set))].mode)))
+	  && partial_subreg_p (GET_MODE (SET_DEST (set)),
+			       vd->e[REGNO (SET_DEST (set))].mode))
 	{
 	  if (noop_move_p (insn))
 	    {