[gcc r12-6550] inliner: Don't emit copy stmts for empty type parameters [PR103989]

[Jakub Jelinek]

https://gcc.gnu.org/g:53ead5787921be799593232cfc9931f916b79002

commit r12-6550-g53ead5787921be799593232cfc9931f916b79002
Author: Jakub Jelinek <jakub@redhat.com>
Date:   Thu Jan 13 15:59:47 2022 +0100

    inliner: Don't emit copy stmts for empty type parameters [PR103989]
    
    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,
    which is caused by ipa inlining happening even at -Og when the post-IPA
    -Og passes don't expect the need to clean up after ipa inlining,
    but I think is desirable anyway.
    
    2022-01-13  Jakub Jelinek  <jakub@redhat.com>
    
            PR tree-optimization/103989
            * tree-inline.c (setup_one_parameter): Don't copy parms with
            empty type.

Diff:
---
 gcc/tree-inline.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/gcc/tree-inline.c b/gcc/tree-inline.c
index d7fc33eb055..8ea8de7e7cb 100644
--- a/gcc/tree-inline.c
+++ b/gcc/tree-inline.c
@@ -3608,7 +3608,7 @@ setup_one_parameter (copy_body_data *id, tree p, tree value, tree fn,
 	      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)