From 161e67441cca56419fea70edf3ea790aff0f7b32 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Bj=C3=B6rn=20Gustavsson?= <bjorn@erlang.org>
Date: Thu, 4 Jan 2018 20:07:09 +0100
Subject: beam_type: Enhance coalescing of allocation instructions

An 'allocate' or 'allocate_zero' instruction should not be
shortly followed by a 'test_heap' instruction. For example,
we don't want this type of code:

    {allocate_zero,3,4}.
    {line,...}.
    {test_heap,7,4}.
    {bif,element,{f,0},...,...}.

While the code is safe because 'allocate_zero' has initialized the
stack frame, it is wasteful. Also note that the code would become
unsafe if the 'allocate_zero' instruction were to be replaced with
an 'allocate' instruction.

What we want to see is this:

    {allocate_heap_zero,3,7,4}.
    {line,...}.
    {bif,element,{f,0},...,...}.
---
 lib/compiler/src/beam_type.erl | 30 +++++++++---------------------
 1 file changed, 9 insertions(+), 21 deletions(-)

(limited to 'lib/compiler/src')

diff --git a/lib/compiler/src/beam_type.erl b/lib/compiler/src/beam_type.erl
index d1f1076e17..e8cca4a0c0 100644
--- a/lib/compiler/src/beam_type.erl
+++ b/lib/compiler/src/beam_type.erl
@@ -333,29 +333,17 @@ flt_need_heap_2({set,_,_,{put_tuple,_}}, H, Fl) ->
     {[],H+1,Fl};
 flt_need_heap_2({set,_,_,put}, H, Fl) ->
     {[],H+1,Fl};
-%% Then the "neutral" instructions. We just pass them.
-flt_need_heap_2({set,[{fr,_}],_,_}, H, Fl) ->
-    {[],H,Fl};
-flt_need_heap_2({set,[],[],fclearerror}, H, Fl) ->
-    {[],H,Fl};
-flt_need_heap_2({set,[],[],fcheckerror}, H, Fl) ->
-    {[],H,Fl};
-flt_need_heap_2({set,_,_,{bif,_,_}}, H, Fl) ->
-    {[],H,Fl};
-flt_need_heap_2({set,_,_,move}, H, Fl) ->
-    {[],H,Fl};
-flt_need_heap_2({set,_,_,{get_tuple_element,_}}, H, Fl) ->
-    {[],H,Fl};
-flt_need_heap_2({set,_,_,get_list}, H, Fl) ->
-    {[],H,Fl};
-flt_need_heap_2({set,_,_,{try_catch,_,_}}, H, Fl) ->
-    {[],H,Fl};
-flt_need_heap_2({set,_,_,init}, H, Fl) ->
-    {[],H,Fl};
-%% All other instructions should cause the insertion of an allocation
+%% The following instructions cause the insertion of an allocation
 %% instruction if needed.
+flt_need_heap_2({set,_,_,{alloc,_,_}}, H, Fl) ->
+    {flt_alloc(H, Fl),0,0};
+flt_need_heap_2({set,_,_,{set_tuple_element,_}}, H, Fl) ->
+    {flt_alloc(H, Fl),0,0};
+flt_need_heap_2({'%live',_,_}, H, Fl) ->
+    {flt_alloc(H, Fl),0,0};
+%% All other instructions are "neutral". We just pass them.
 flt_need_heap_2(_, H, Fl) ->
-    {flt_alloc(H, Fl),0,0}.
+    {[],H,Fl}.
 
 flt_alloc(0, 0) ->
     [];
-- 
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