From 37225949b6cf177934848fff21a1a551b7f6faee Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Bj=C3=B6rn=20Gustavsson?= <bjorn@erlang.org>
Date: Wed, 15 Apr 2015 09:59:05 +0200
Subject: beam_block: Optimize matching of binary literals

When matching a binary literal as in:

  <<"abc">> = Bin

the compiler will produce a sequence of three instructions
(some details in the instructions removed for simplicity):

  bs_start_match2 Fail BinReg CtxtReg
  bs_match_string Fail CtxtReg "abc"
  bs_test_tail2 Fail CtxtReg 0

The sequence can be replaced with:

  is_eq_exact Fail BinReg "abc"
---
 lib/compiler/src/beam_dead.erl       | 10 ++++++++++
 lib/compiler/test/bs_match_SUITE.erl | 14 ++++++++++++--
 2 files changed, 22 insertions(+), 2 deletions(-)

(limited to 'lib')

diff --git a/lib/compiler/src/beam_dead.erl b/lib/compiler/src/beam_dead.erl
index adc3cebc62..5932d8ce1d 100644
--- a/lib/compiler/src/beam_dead.erl
+++ b/lib/compiler/src/beam_dead.erl
@@ -255,6 +255,16 @@ backward([{jump,{f,To}}=J|[{bif,Op,_,Ops,Reg}|Is]=Is0], D, Acc) ->
     catch
 	throw:not_possible -> backward(Is0, D, [J|Acc])
     end;
+backward([{test,bs_start_match2,F,_,[R,_],Ctxt}=I|Is], D,
+	 [{test,bs_match_string,F,[Ctxt,Bs]},
+	  {test,bs_test_tail2,F,[Ctxt,0]}|Acc0]=Acc) ->
+    case beam_utils:is_killed(Ctxt, Acc0, D) of
+	true ->
+	    Eq = {test,is_eq_exact,F,[R,{literal,Bs}]},
+	    backward(Is, D, [Eq|Acc0]);
+	false ->
+	    backward(Is, D, [I|Acc])
+    end;
 backward([{test,bs_start_match2,{f,To0},Live,[Src|_]=Info,Dst}|Is], D, Acc) ->
     To = shortcut_bs_start_match(To0, Src, D),
     I = {test,bs_start_match2,{f,To},Live,Info,Dst},
diff --git a/lib/compiler/test/bs_match_SUITE.erl b/lib/compiler/test/bs_match_SUITE.erl
index 80d80505a6..b54db06339 100644
--- a/lib/compiler/test/bs_match_SUITE.erl
+++ b/lib/compiler/test/bs_match_SUITE.erl
@@ -34,7 +34,8 @@
 	 otp_7188/1,otp_7233/1,otp_7240/1,otp_7498/1,
 	 match_string/1,zero_width/1,bad_size/1,haystack/1,
 	 cover_beam_bool/1,matched_out_size/1,follow_fail_branch/1,
-	 no_partition/1,calling_a_binary/1,binary_in_map/1]).
+	 no_partition/1,calling_a_binary/1,binary_in_map/1,
+	 match_string_opt/1]).
 
 -export([coverage_id/1,coverage_external_ignore/2]).
 
@@ -59,7 +60,8 @@ groups() ->
        matching_and_andalso,otp_7188,otp_7233,otp_7240,
        otp_7498,match_string,zero_width,bad_size,haystack,
        cover_beam_bool,matched_out_size,follow_fail_branch,
-       no_partition,calling_a_binary,binary_in_map]}].
+       no_partition,calling_a_binary,binary_in_map,
+       match_string_opt]}].
 
 
 init_per_suite(Config) ->
@@ -1214,6 +1216,14 @@ match_binary_in_map(Map) ->
 	    ok
     end.
 
+match_string_opt(Config) when is_list(Config) ->
+    {x,<<1,2,3>>,{<<1>>,{v,<<1,2,3>>}}} =
+	do_match_string_opt({<<1>>,{v,<<1,2,3>>}}),
+    ok.
+
+do_match_string_opt({<<1>>,{v,V}}=T) ->
+    {x,V,T}.
+
 
 check(F, R) ->
     R = F().
-- 
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