1 files changed, 46 insertions, 22 deletions

diff --git a/lib/compiler/src/beam_bsm.erl b/lib/compiler/src/beam_bsm.erl
index 37053e1cc4..02794a8e18 100644
--- a/lib/compiler/src/beam_bsm.erl
+++ b/lib/compiler/src/beam_bsm.erl
@@ -241,21 +241,45 @@ btb_reaches_match_2([{bif,_,{f,F},Ss,Dst}=I|Is], Regs0, D0) ->
     Regs = btb_kill([Dst], Regs0),
     D = btb_follow_branch(F, Regs, D0),
     btb_reaches_match_1(Is, Regs, D);
-btb_reaches_match_2([{test,bs_start_match2,_,_,[Ctx,_],Ctx}|Is], Regs, D) ->
-    case btb_context_regs(Regs) of
-	[Ctx] ->
-	    D;
-	CtxRegs ->
-	    case member(Ctx, CtxRegs) of
-		false -> btb_reaches_match_2(Is, Regs, D);
-		true -> btb_error(unsuitable_bs_start_match)
+btb_reaches_match_2([{test,bs_start_match2,{f,F},Live,[Ctx,_],Ctx}=I|Is],
+		    Regs0, D0) ->
+    CtxRegs = btb_context_regs(Regs0),
+    case member(Ctx, CtxRegs) of
+	false ->
+	    %% This bs_start_match2 instruction does not use "our"
+	    %% match state. Therefore we can continue the search
+	    %% for another bs_start_match2 instruction.
+	    D = btb_follow_branch(F, Regs0, D0),
+	    Regs = btb_kill_not_live(Live, Regs0),
+	    btb_reaches_match_2(Is, Regs, D);
+	true ->
+	    %% OK. This instruction will use "our" match state,
+	    %% but we must make sure that all other copies of the
+	    %% match state are killed in the code that follows
+	    %% the instruction. (We know that the fail branch cannot
+	    %% be taken in this case.)
+	    OtherCtxRegs = CtxRegs -- [Ctx],
+	    case btb_are_all_unused(OtherCtxRegs, Is, D0) of
+		false -> btb_error({OtherCtxRegs,not_all_unused_after,I});
+		true -> D0
 	    end
     end;
-btb_reaches_match_2([{test,bs_start_match2,_,_,[Bin,_],Ctx}|Is], Regs, D) ->
-    CtxRegs = btb_context_regs(Regs),
+btb_reaches_match_2([{test,bs_start_match2,{f,F},Live,[Bin,_],Ctx}|Is],
+		    Regs0, D0) ->
+    CtxRegs = btb_context_regs(Regs0),
     case member(Bin, CtxRegs) orelse member(Ctx, CtxRegs) of
-	false -> btb_reaches_match_2(Is, Regs, D);
-	true -> btb_error(unsuitable_bs_start_match)
+	false ->
+	    %% This bs_start_match2 does not reference any copy of the
+	    %% match state. Therefore it can safely be passed on the
+	    %% way to another (perhaps more suitable) bs_start_match2
+	    %% instruction.
+	    D = btb_follow_branch(F, Regs0, D0),
+	    Regs = btb_kill_not_live(Live, Regs0),
+	    btb_reaches_match_2(Is, Regs, D);
+	true ->
+	    %% This variant of the bs_start_match2 instruction does
+	    %% not accept a match state as source.
+	    btb_error(unsuitable_bs_start_match)
     end;
 btb_reaches_match_2([{test,_,{f,F},Ss}=I|Is], Regs, D0) ->
     btb_ensure_not_used(Ss, I, Regs),
@@ -287,11 +311,11 @@ btb_reaches_match_2([{bs_restore2,Src,_}=I|Is], Regs0, D) ->
 	    btb_reaches_match_1(Is, Regs0, D);
 	true ->
 	    %% Check that all other copies of the context registers
-	    %% are killed by the following instructions.
+	    %% are unused by the following instructions.
 	    Regs = btb_kill([Src], Regs0),
 	    CtxRegs = btb_context_regs(Regs),
-	    case btb_are_all_killed(CtxRegs, Is, D) of
-		false -> btb_error({CtxRegs,not_all_killed_after,I});
+	    case btb_are_all_unused(CtxRegs, Is, D) of
+		false -> btb_error({CtxRegs,not_all_unused_after,I});
 		true -> D#btb{must_not_save=true}
 	    end
     end;
@@ -301,11 +325,11 @@ btb_reaches_match_2([{bs_context_to_binary,Src}=I|Is], Regs0, D) ->
 	    btb_reaches_match_1(Is, Regs0, D);
 	true ->
 	    %% Check that all other copies of the context registers
-	    %% are killed by the following instructions.
+	    %% are unused by the following instructions.
 	    Regs = btb_kill([Src], Regs0),
 	    CtxRegs = btb_context_regs(Regs),
-	    case btb_are_all_killed(CtxRegs, Is, D) of
-		false -> btb_error({CtxRegs,not_all_killed_after,I});
+	    case btb_are_all_unused(CtxRegs, Is, D) of
+		false -> btb_error({CtxRegs,not_all_unused_after,I});
 		true -> D#btb{must_not_save=true}
 	    end
     end;
@@ -343,7 +367,7 @@ btb_call(Arity, Lbl, Regs0, Is, D0) ->
 	    %% tucked away in a y register.
 	    RegList = btb_context_regs(Regs),
 	    YRegs = [R || {y,_}=R <- RegList],
-	    case btb_are_all_killed(YRegs, Is, D) of
+	    case btb_are_all_unused(YRegs, Is, D) of
 		true -> D;
 		false -> btb_error({multiple_uses,RegList})
 	    end;
@@ -426,11 +450,11 @@ btb_reaches_match_block([], Regs) ->
     Regs.
 
 %% btb_are_all_killed([Register], [Instruction], D) -> true|false
-%%  Test whether all of the register are killed in the instruction stream.
+%%  Test whether all of the register are unused in the instruction stream.
 
-btb_are_all_killed(RegList, Is, #btb{index=Li}) ->
+btb_are_all_unused(RegList, Is, #btb{index=Li}) ->
     all(fun(R) ->
-		beam_utils:is_killed(R, Is, Li)
+		beam_utils:is_not_used(R, Is, Li)
 	end, RegList).
 
 %% btp_regs_from_list([Register]) -> RegisterSet.