[gcc r15-1606] Revert one of the force_subreg changes

[Richard Sandiford]

https://gcc.gnu.org/g:b694bf417cdd7d0a4d78e9927bab6bc202b7df6c

commit r15-1606-gb694bf417cdd7d0a4d78e9927bab6bc202b7df6c
Author: Richard Sandiford <richard.sandiford@arm.com>
Date:   Tue Jun 25 09:41:21 2024 +0100

    Revert one of the force_subreg changes
    
    One of the changes in g:d4047da6a070175aae7121c739d1cad6b08ff4b2
    caused a regression in ft32-elf; see:
    
        https://gcc.gnu.org/pipermail/gcc-patches/2024-June/655418.html
    
    for details.  This change was different from the others in that the
    original call was to simplify_subreg rather than simplify_lowpart_subreg.
    The old code would therefore go on to do the force_reg for more cases
    than the new code would.
    
    gcc/
            * expmed.cc (store_bit_field_using_insv): Revert earlier change
            to use force_subreg instead of simplify_gen_subreg.

Diff:
---
 gcc/expmed.cc | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/gcc/expmed.cc b/gcc/expmed.cc
index 3b9475f5aa0..8bbbc94a98c 100644
--- a/gcc/expmed.cc
+++ b/gcc/expmed.cc
@@ -695,7 +695,13 @@ store_bit_field_using_insv (const extraction_insn *insv, rtx op0,
 	     if we must narrow it, be sure we do it correctly.  */
 
 	  if (GET_MODE_SIZE (value_mode) < GET_MODE_SIZE (op_mode))
-	    tmp = force_subreg (op_mode, value1, value_mode, 0);
+	    {
+	      tmp = simplify_subreg (op_mode, value1, value_mode, 0);
+	      if (! tmp)
+		tmp = simplify_gen_subreg (op_mode,
+					   force_reg (value_mode, value1),
+					   value_mode, 0);
+	    }
 	  else
 	    {
 	      if (targetm.mode_rep_extended (op_mode, value_mode) != UNKNOWN)