From af632b4a9f259f5b8779d23d7aea6ebab7196724 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Bj=C3=B6rn=20Gustavsson?= <bjorn@erlang.org>
Date: Thu, 20 Sep 2018 07:57:19 +0200
Subject: Move allocation combining from beam_flatten to beam_ssa_codegen

Continuing the simplification of beam_flatten, move the optimization
that eliminates a test_heap instruction following a binary construction
by incorporating the allocation of the heap space into the bs_init*
instruction itself.

This change does not change the generated code in any way.

Also remove beam_utils:combine_heap_needs/2, because beam_flatten
was the last user of it.
---
 lib/compiler/src/beam_flatten.erl | 33 +--------------------------------
 1 file changed, 1 insertion(+), 32 deletions(-)

(limited to 'lib/compiler/src/beam_flatten.erl')

diff --git a/lib/compiler/src/beam_flatten.erl b/lib/compiler/src/beam_flatten.erl
index c8bc1b7b84..07c24abf7b 100644
--- a/lib/compiler/src/beam_flatten.erl
+++ b/lib/compiler/src/beam_flatten.erl
@@ -42,13 +42,6 @@ block([{block,Is0}|Is1], Acc) -> block(Is1, norm_block(Is0, Acc));
 block([I|Is], Acc) -> block(Is, [I|Acc]);
 block([], Acc) -> reverse(Acc).
 
-norm_block([{set,[],[],{alloc,R,{_,nostack,_,_}=Alloc}}|Is], Acc0) ->
-    case insert_alloc_in_bs_init(Acc0, Alloc) of
-	impossible ->
-	    norm_block(Is, reverse(norm_allocate(Alloc, R), Acc0));
-	Acc ->
-	    norm_block(Is, Acc)
-    end;
 norm_block([{set,[],[],{alloc,R,Alloc}}|Is], Acc0) ->
     norm_block(Is, reverse(norm_allocate(Alloc, R), Acc0));
 norm_block([{set,[D1],[S],get_hd},{set,[D2],[S],get_tl}|Is], Acc) ->
@@ -56,7 +49,7 @@ norm_block([{set,[D1],[S],get_hd},{set,[D2],[S],get_tl}|Is], Acc) ->
     norm_block(Is, [I|Acc]);
 norm_block([I|Is], Acc) -> norm_block(Is, [norm(I)|Acc]);
 norm_block([], Acc) -> Acc.
-    
+
 norm({set,[D],As,{bif,N,F}})      -> {bif,N,F,As,D};
 norm({set,[D],As,{alloc,R,{gc_bif,N,F}}}) -> {gc_bif,N,F,R,As,D};
 norm({set,[D],[],init})           -> {init,D};
@@ -90,27 +83,3 @@ norm_allocate({nozero,Ns,0,Inits}, Regs) ->
     [{allocate,Ns,Regs}|Inits];
 norm_allocate({nozero,Ns,Nh,Inits}, Regs) ->
     [{allocate_heap,Ns,Nh,Regs}|Inits].
-
-%% insert_alloc_in_bs_init(ReverseInstructionStream, AllocationInfo) ->
-%%                                  impossible | ReverseInstructionStream'
-%%   A bs_init/6 instruction should not be followed by a test heap instruction.
-%%   Given the AllocationInfo from a test heap instruction, merge the
-%%   allocation amounts into the previous bs_init/6 instruction (if any).
-%%
-insert_alloc_in_bs_init([{bs_put,_,_,_}=I|Is], Alloc) ->
-    %% The instruction sequence ends with an bs_put/4 instruction.
-    %% We'll need to search backwards for the bs_init/6 instruction.
-    insert_alloc_1(Is, Alloc, [I]);
-insert_alloc_in_bs_init(_, _) -> impossible.
-
-insert_alloc_1([{bs_init=Op,Fail,Info0,Live,Ss,Dst}|Is],
-	       {_,nostack,Ws2,[]}, Acc) when is_integer(Live) ->
-    %% The number of extra heap words is always in the second position
-    %% in the Info tuple.
-    Ws1 = element(2, Info0),
-    Al = beam_utils:combine_heap_needs(Ws1, Ws2),
-    Info = setelement(2, Info0, Al),
-    I = {Op,Fail,Info,Live,Ss,Dst},
-    reverse(Acc, [I|Is]);
-insert_alloc_1([{bs_put,_,_,_}=I|Is], Alloc, Acc) ->
-    insert_alloc_1(Is, Alloc, [I|Acc]).
-- 
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