From e914206e11b439a5794b7a8c3c527af395609ddd Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Bj=C3=B6rn=20Gustavsson?= <bjorn@erlang.org>
Date: Wed, 31 Dec 2014 11:11:57 +0100
Subject: sys_core_fold: Improve optimization of 'not'

Optimize away 'not' in sys_core_fold instead of in beam_block
and beam_dead, as we can do a better job in sys_core_fold.

I modified the test suite temporarily to never turn off Core Erlang
modifications and looked at the coverage. With the new optimizations
active in sys_core_fold, the code in beam_block and beam_dead did not
find a single 'not' that it could optimize.  That proves that the new
optimization is at least as good as the old one. Manually, I could
also verify that the new optimization would optimize some variations
of 'not' that the old one would not handle.
---
 lib/compiler/src/beam_block.erl | 19 -------------------
 1 file changed, 19 deletions(-)

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

diff --git a/lib/compiler/src/beam_block.erl b/lib/compiler/src/beam_block.erl
index 92f09e400c..5216f39296 100644
--- a/lib/compiler/src/beam_block.erl
+++ b/lib/compiler/src/beam_block.erl
@@ -252,13 +252,6 @@ combine_alloc({_,Ns,Nh1,Init}, {_,nostack,Nh2,[]})  ->
 %% opt([Instruction]) -> [Instruction]
 %%  Optimize the instruction stream inside a basic block.
 
-opt([{set,[Dst],As,{bif,Bif,Fail}}=I1,
-     {set,[Dst],[Dst],{bif,'not',Fail}}=I2|Is]) ->
-    %% Get rid of the 'not' if the operation can be inverted.
-    case inverse_comp_op(Bif) of
- 	none -> [I1,I2|opt(Is)];
- 	RevBif -> [{set,[Dst],As,{bif,RevBif,Fail}}|opt(Is)]
-    end;
 opt([{set,[X],[X],move}|Is]) -> opt(Is);
 opt([{set,_,_,{line,_}}=Line1,
      {set,[D1],[{integer,Idx1},Reg],{bif,element,{f,0}}}=I1,
@@ -428,18 +421,6 @@ x_live([{x,N}|Rs], Regs) -> x_live(Rs, Regs bor (1 bsl N));
 x_live([_|Rs], Regs) -> x_live(Rs, Regs);
 x_live([], Regs) -> Regs.
 
-%% inverse_comp_op(Op) -> none|RevOp
-
-inverse_comp_op('=:=') -> '=/=';
-inverse_comp_op('=/=') -> '=:=';
-inverse_comp_op('==') -> '/=';
-inverse_comp_op('/=') -> '==';
-inverse_comp_op('>') -> '=<';
-inverse_comp_op('<') -> '>=';
-inverse_comp_op('>=') -> '<';
-inverse_comp_op('=<') -> '>';
-inverse_comp_op(_) -> none.
-
 %%%
 %%% Evaluation of constant bit fields.
 %%%
-- 
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