[PATCH] inliner: Don't emit copy stmts for empty type parameters [PR103989]

[Jakub Jelinek via Gcc-patches]

Hi!

The following patch avoids emitting a parameter copy statement when inlining
if the parameter has empty type.  E.g. the gimplifier does something similar
(except that it needs to evaluate side-effects if any, which isn't the case
here):
  /* For empty types only gimplify the left hand side and right hand
     side as statements and throw away the assignment.  Do this after
     gimplify_modify_expr_rhs so we handle TARGET_EXPRs of addressable
     types properly.  */
  if (is_empty_type (TREE_TYPE (*from_p))
      && !want_value
      /* Don't do this for calls that return addressable types, expand_call
         relies on those having a lhs.  */
      && !(TREE_ADDRESSABLE (TREE_TYPE (*from_p))
           && TREE_CODE (*from_p) == CALL_EXPR))
    {
      gimplify_stmt (from_p, pre_p);
      gimplify_stmt (to_p, pre_p);
      *expr_p = NULL_TREE;
      return GS_ALL_DONE;
    }
Unfortunately, this patch doesn't cure the uninit warnings in that PR,
but I think is desirable anyway.

Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?

2022-01-13  Jakub Jelinek  <ja...@redhat.com>

        PR tree-optimization/103989
        * tree-inline.c (setup_one_parameter): Don't copy parms with
        empty type.

--- gcc/tree-inline.c.jj        2022-01-11 23:11:23.422275652 +0100
+++ gcc/tree-inline.c   2022-01-12 18:37:44.119950128 +0100
@@ -3608,7 +3608,7 @@ setup_one_parameter (copy_body_data *id,
              init_stmt = gimple_build_assign (def, rhs);
            }
        }
-      else
+      else if (!is_empty_type (TREE_TYPE (var)))
         init_stmt = gimple_build_assign (var, rhs);
 
       if (bb && init_stmt)

        Jakub