[Bug middle-end/98190] [11 Regression] GCC11 miscompiles code using _Bool when inlining: bfxil instruction misused since r11-165

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98190

--- Comment #12 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
(In reply to rsandifo@gcc.gnu.org from comment #10)
> If we can't assert, I guess the rule is that we need to extend
> whenever we're storing to the MSB of the inner register.  We can
> do that either by extending the source value and the range to
> the outer register, or by assigning to the inner register and
> then extending it separately.

So perhaps:
--- gcc/expr.c.jj       2020-12-09 00:00:08.622548080 +0100
+++ gcc/expr.c  2020-12-09 10:36:12.198801940 +0100
@@ -5451,6 +5451,33 @@ expand_assignment (tree to, tree from, b
                                               mode1, to_rtx, to, from,
                                               reversep))
            result = NULL;
+          else if (SUBREG_P (to_rtx)
+                  && SUBREG_PROMOTED_VAR_P (to_rtx))
+           {
+             /* If to_rtx is a promoted subreg, this must be a store to the
+                whole variable, otherwise to_rtx would need to be MEM.
+                We need to zero or sign extend the value afterwards.  */
+             gcc_assert (known_eq (bitpos, 0)
+                         && known_eq (bitsize,
+                                      GET_MODE_BITSIZE (GET_MODE (to_rtx))));
+             if (TREE_CODE (to) == MEM_REF && !REF_REVERSE_STORAGE_ORDER (to))
+               result = store_expr (from, to_rtx, 0, nontemporal, false);
+             else
+               {
+                 result = store_field (to_rtx, bitsize, bitpos,
+                                       bitregion_start, bitregion_end,
+                                       mode1, from, get_alias_set (to),
+                                       nontemporal, reversep);
+                 rtx to_rtx1
+                   = lowpart_subreg (subreg_unpromoted_mode (to_rtx),
+                                     SUBREG_REG (to_rtx),
+                                     subreg_promoted_mode (to_rtx));
+                 to_rtx1 = convert_to_mode (subreg_promoted_mode (to_rtx),
+                                            to_rtx1,
+                                            SUBREG_PROMOTED_SIGN (to_rtx));
+                 emit_move_insn (SUBREG_REG (to_rtx), to_rtx1);
+               }
+           }
          else
            result = store_field (to_rtx, bitsize, bitpos,
                                  bitregion_start, bitregion_end,

then?  As in, if store_expr can handle it, use that, otherwise perform the
extension at the end.

As for BIT_INSERT_EXPR, I'm not sure if SSA_NAMEs can get promoted SUBREGs or
not, but in any case it wouldn't be this code path, it would be store_expr
which handles the promoted SUBREGs already, because destination would not be a
MEM_REF with non-mem decl or reversed order, nor handled_component_p, nor
ARRAY_TYPE destination.