[gcc r12-4428] middle-end/102682 - avoid invalid subreg on the LHS

[Richard Biener <rguenth@gcc.gnu.org>]

https://gcc.gnu.org/g:147ed0184f403b51b4f180f94b0779e9905faa3a

commit r12-4428-g147ed0184f403b51b4f180f94b0779e9905faa3a
Author: Richard Biener <rguenther@suse.de>
Date:   Mon Oct 11 14:08:52 2021 +0200

    middle-end/102682 - avoid invalid subreg on the LHS
    
    The following avoids generating
    
    (insn 6 5 7 2 (set (subreg:OI (concatn/v:TI [
                        (reg:DI 92 [ buffer ])
                        (reg:DI 93 [ buffer+8 ])
                    ]) 0)
            (subreg:OI (reg/v:V8SI 85 [ __x ]) 0)) "t.ii":76:21 74 {*movoi_internal_avx}
         (nil))
    
    via store_bit_field_1 when we try to store excess data into
    a register allocated temporary.  The case was supposed to
    
          /* Use the subreg machinery either to narrow OP0 to the required
             words...
    
    but the check ensured only an register-aligned but not a large
    enough piece.  The following adds such missed check which ends up
    decomposing the set to
    
    (insn 6 5 7 (set (subreg:DI (reg/v:TI 84 [ buffer ]) 0)
            (subreg:DI (reg/v:V8SI 85 [ __x ]) 0)) "t.ii":76:21 -1
         (nil))
    
    (insn 7 6 0 (set (subreg:DI (reg/v:TI 84 [ buffer ]) 8)
            (subreg:DI (reg/v:V8SI 85 [ __x ]) 8)) "t.ii":76:21 -1
         (nil))
    
    2021-10-11  Richard Biener  <rguenther@suse.de>
    
            PR middle-end/102682
            * expmed.c (store_bit_field_1): Ensure a LHS subreg would
            not create a paradoxical subreg.

Diff:
---
 gcc/expmed.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/gcc/expmed.c b/gcc/expmed.c
index 59734d4841c..bbdd0e71d20 100644
--- a/gcc/expmed.c
+++ b/gcc/expmed.c
@@ -806,7 +806,8 @@ store_bit_field_1 (rtx str_rtx, poly_uint64 bitsize, poly_uint64 bitnum,
 	    }
 	}
       else if (constant_multiple_p (bitnum, regsize * BITS_PER_UNIT, &regnum)
-	       && multiple_p (bitsize, regsize * BITS_PER_UNIT))
+	       && multiple_p (bitsize, regsize * BITS_PER_UNIT)
+	       && known_ge (GET_MODE_BITSIZE (GET_MODE (op0)), bitsize))
 	{
 	  sub = simplify_gen_subreg (fieldmode, op0, GET_MODE (op0),
 				     regnum * regsize);