Reinstate optimization of binary literal matching

105c5b0071 was reverted in dd1162846e because clauses that were
supposed to match would not match. (See 8b83bc0b.)

Reintroduce the optimization, but make sure that we only shortcut
bs_context_to_binary instructions and not bs_start_match2 instructions.

1 files changed, 21 insertions, 2 deletions

diff --git a/lib/compiler/src/beam_dead.erl b/lib/compiler/src/beam_dead.erl
index 6f6d742293..3606af9d75 100644
--- a/lib/compiler/src/beam_dead.erl
+++ b/lib/compiler/src/beam_dead.erl
@@ -272,14 +272,18 @@ 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,
+backward([{test,bs_start_match2,F,Live,[R,_]=Args,Ctxt}|Is], D,
 	 [{test,bs_match_string,F,[Ctxt,Bs]},
 	  {test,bs_test_tail2,F,[Ctxt,0]}|Acc0]=Acc) ->
+    {f,To0} = F,
     case beam_utils:is_killed(Ctxt, Acc0, D) of
 	true ->
-	    Eq = {test,is_eq_exact,F,[R,{literal,Bs}]},
+	    To = shortcut_bs_context_to_binary(To0, R, D),
+	    Eq = {test,is_eq_exact,{f,To},[R,{literal,Bs}]},
 	    backward(Is, D, [Eq|Acc0]);
 	false ->
+	    To = shortcut_bs_start_match(To0, R, D),
+	    I = {test,bs_start_match2,{f,To},Live,Args,Ctxt},
 	    backward(Is, D, [I|Acc])
     end;
 backward([{test,bs_start_match2,{f,To0},Live,[Src|_]=Info,Dst}|Is], D, Acc) ->
@@ -551,6 +555,21 @@ shortcut_bs_start_match_1([{test,bs_start_match2,{f,To},_,[Reg|_],_}|_],
 shortcut_bs_start_match_1(_, _, To, _) ->
     To.
 
+%% shortcut_bs_context_to_binary(TargetLabel, Reg) -> TargetLabel
+%%  If a bs_start_match2 instruction has been eliminated, the
+%%  bs_context_to_binary instruction can be eliminated too.
+
+shortcut_bs_context_to_binary(To, Reg, D) ->
+    shortcut_bs_ctb_1(beam_utils:code_at(To, D), Reg, To, D).
+
+shortcut_bs_ctb_1([{bs_context_to_binary,Reg}|Is], Reg, To, D) ->
+    shortcut_bs_ctb_1(Is, Reg, To, D);
+shortcut_bs_ctb_1([{jump,{f,To}}|_], Reg, _, D) ->
+    Code = beam_utils:code_at(To, D),
+    shortcut_bs_ctb_1(Code, Reg, To, D);
+shortcut_bs_ctb_1(_, _, To, _) ->
+    To.
+
 %% shortcut_rel_op(FailLabel, Operator, [Operand], D) -> FailLabel'
 %%  Try to shortcut the given test instruction. Example:
 %%