https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94482
--- Comment #20 from Richard Biener <rguenth at gcc dot gnu.org> --- (In reply to Richard Biener from comment #19) > gcc.dg/torture/pr52244.c ICEs on the generated > > VIEW_CONVERT_EXPR<union u_t>(u) = bar (); > > since V_C_E on the LHS are generally unwanted (but Ada has them for > aggregates > just not in outermost position). What's always possible on the LHS is > to use a BIT_FIELD_REF. So the issue here is that 'u' is a register, not that V_C_E on the LHS are invalid. And we don't have a "general" DECL_GIMPLE_REG_P we could unset since that's just usd for complex and vector types. Which means we'd have to artifically set TREE_ADDRESSABLE on the replacement. It isn't grp_partial_lhs so SRA doesn't do that. In the case of a call we can't move the V_C_E to the RHS so we'd really need to keep the call and insert a compensation assignment. orig = bar (); u = VIEW_CONVERT <regtype> (orig); but that doesn't work for a partial access since we're clobbering the whole replacement here. A BIT_FIELD_REF on the LHS for a _register_ is also not possible so the write to a part via an incompatible type would represent itself as orig_full = VIEW_CONVERT <orig_type> (repl_full); <original stmt with partial write to orig_full> repl_full = VIEW_CONVERT <repl_type> (orig_full); which of course makes this highly suboptimal (but at least correct which is what we should focus on right now).
