Eliminate get_list/3 internally in the compiler

Instructions that produce more than one result complicate
optimizations. get_list/3 is one of two instructions that
produce multiple results (get_map_elements/3 is the other).

Introduce the get_hd/2 and get_tl/2 instructions
that return the head and tail of a cons cell, respectively,
and use it internally in all optimization passes.

For efficiency, we still want to use get_list/3 if both
head and tail are used, so we will translate matching pairs
of get_hd and get_tl back to get_list instructions.

1 files changed, 10 insertions, 0 deletions

diff --git a/lib/hipe/icode/hipe_beam_to_icode.erl b/lib/hipe/icode/hipe_beam_to_icode.erl
index 6e66ec057c..f429d40272 100644
--- a/lib/hipe/icode/hipe_beam_to_icode.erl
+++ b/lib/hipe/icode/hipe_beam_to_icode.erl
@@ -605,6 +605,16 @@ trans_fun([{get_list,List,Head,Tail}|Instructions], Env) ->
       ?error_msg("hd and tl regs identical in get_list~n",[]),
       erlang:error(not_handled)
   end;
+%%--- get_hd ---
+trans_fun([{get_hd,List,Head}|Instructions], Env) ->
+  TransList = [trans_arg(List)],
+  I = hipe_icode:mk_primop([mk_var(Head)],unsafe_hd,TransList),
+  [I | trans_fun(Instructions,Env)];
+%%--- get_tl ---
+trans_fun([{get_tl,List,Tail}|Instructions], Env) ->
+  TransList = [trans_arg(List)],
+  I = hipe_icode:mk_primop([mk_var(Tail)],unsafe_tl,TransList),
+  [I | trans_fun(Instructions,Env)];
 %%--- get_tuple_element ---
 trans_fun([{get_tuple_element,Xreg,Index,Dst}|Instructions], Env) ->
   I = hipe_icode:mk_primop([mk_var(Dst)],