From 3abba595d91506f32aba47ecc39e9b6b3a08f645 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Magnus=20L=C3=A5ng?= <margnus1@telia.com>
Date: Mon, 21 Nov 2016 17:39:56 +0100
Subject: hipe_beam_to_icode: Omit redtest in some closures

This is useful to generate shorter code for closures generated by
(fun F/A).
---
 lib/hipe/icode/hipe_beam_to_icode.erl | 31 ++++++++++++++++++++-----------
 1 file changed, 20 insertions(+), 11 deletions(-)

(limited to 'lib')

diff --git a/lib/hipe/icode/hipe_beam_to_icode.erl b/lib/hipe/icode/hipe_beam_to_icode.erl
index 100bc0b0e2..610578dfbc 100644
--- a/lib/hipe/icode/hipe_beam_to_icode.erl
+++ b/lib/hipe/icode/hipe_beam_to_icode.erl
@@ -148,7 +148,8 @@ trans_mfa_code(M,F,A, FunBeamCode, ClosureInfo) ->
 		  {Code3,_Env3} = mk_debug_calltrace(MFA, Env1, Code2),
 		  {Code3,_Env3} = {Code2,Env1}),
   %% For stack optimization
-  Leafness = leafness(Code3),
+  IsClosure = get_closure_info(MFA, ClosureInfo) =/= not_a_closure,
+  Leafness = leafness(Code3, IsClosure),
   IsLeaf = is_leaf_code(Leafness),
   Code4 =
     [FunLbl |
@@ -156,7 +157,6 @@ trans_mfa_code(M,F,A, FunBeamCode, ClosureInfo) ->
        false -> Code3;
        true -> [mk_redtest()|Code3]
      end],
-  IsClosure = get_closure_info(MFA, ClosureInfo) =/= not_a_closure,
   Code5 = hipe_icode:mk_icode(MFA, FunArgs, IsClosure, IsLeaf,
 			      remove_dead_code(Code4),
 			      hipe_gensym:var_range(icode),
@@ -173,12 +173,12 @@ trans_mfa_code(M,F,A, FunBeamCode, ClosureInfo) ->
 
 mk_redtest() -> hipe_icode:mk_primop([], redtest, []).
 
-leafness(Is) -> % -> true, selfrec, or false
-  leafness(Is, true).
+leafness(Is, IsClosure) -> % -> true, selfrec, closure, or false
+  leafness(Is, IsClosure, true).
 
-leafness([], Leafness) ->
+leafness([], _IsClosure, Leafness) ->
   Leafness;
-leafness([I|Is], Leafness) ->
+leafness([I|Is], IsClosure, Leafness) ->
   case I of
     #icode_comment{} ->
       %% BEAM self-tailcalls become gotos, but they leave
@@ -191,7 +191,7 @@ leafness([I|Is], Leafness) ->
 	  'self_tail_recursive' -> selfrec;	% call_only to selfrec
 	  _ -> Leafness
 	end,
-      leafness(Is, NewLeafness);
+      leafness(Is, IsClosure, NewLeafness);
     #icode_call{} ->
       case hipe_icode:call_type(I) of
 	'primop' -> 
@@ -199,12 +199,12 @@ leafness([I|Is], Leafness) ->
 	    call_fun -> false;		% Calls closure
 	    enter_fun -> false;		% Calls closure
 	    #apply_N{} -> false;
-	    _ -> leafness(Is, Leafness)	% Other primop calls are ok
+	    _ -> leafness(Is, IsClosure, Leafness) % Other primop calls are ok
 	  end;
 	T when T =:= 'local' orelse T =:= 'remote' ->
 	  {M,F,A} = hipe_icode:call_fun(I),
 	  case erlang:is_builtin(M, F, A) of
-	    true -> leafness(Is, Leafness);
+	    true -> leafness(Is, IsClosure, Leafness);
 	    false -> false
 	  end
       end;
@@ -223,11 +223,12 @@ leafness([I|Is], Leafness) ->
 	T when T =:= 'local' orelse T =:= 'remote' ->
 	  {M,F,A} = hipe_icode:enter_fun(I),
 	  case erlang:is_builtin(M, F, A) of
-	    true -> leafness(Is, Leafness);
+	    true -> leafness(Is, IsClosure, Leafness);
+	    _ when IsClosure -> leafness(Is, IsClosure, closure);
 	    _ -> false
 	  end
       end;
-    _ -> leafness(Is, Leafness)
+    _ -> leafness(Is, IsClosure, Leafness)
   end.
 
 %% XXX: this old stuff is passed around but essentially unused
@@ -235,12 +236,20 @@ is_leaf_code(Leafness) ->
   case Leafness of
     true -> true;
     selfrec -> true;
+    closure -> false;
     false -> false
   end.
 
 needs_redtest(Leafness) ->
   case Leafness of
     true -> false;
+    %% A "leaf" closure may contain tailcalls to non-closures in addition to
+    %% what other leaves may contain. Omitting the redtest is useful to generate
+    %% shorter code for closures generated by (fun F/A), and is safe since
+    %% control flow cannot return to a "leaf" closure again without a reduction
+    %% being consumed. This is true since no function that can call a closure
+    %% will ever have its redtest omitted.
+    closure -> false;
     selfrec -> true;
     false -> true
   end.
-- 
cgit v1.2.3