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authorBjörn Gustavsson <[email protected]>2018-02-28 15:51:26 +0100
committerBjörn Gustavsson <[email protected]>2018-03-01 12:10:52 +0100
commitebe7556088694c1541bd45f5e978ab02f38c36dc (patch)
tree16a19c52fe0a7834814d90877e944dcc7f188b34
parente97bef322f6bd1701b1dd4b936efdf32562bcbfe (diff)
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beam_utils: Correct the liveness calulcations in live_opt/1
live_opt_block/4 could overestimate the number of live registers for a GC BIF and trigger an assertion. This does not seem to be a problem when generating code using v3_codegen, but only when using a new experimental code generator, therefore there is no need include this correction in maint.
-rw-r--r--lib/compiler/src/beam_utils.erl75
1 files changed, 40 insertions, 35 deletions
diff --git a/lib/compiler/src/beam_utils.erl b/lib/compiler/src/beam_utils.erl
index 7031fe8bfe..814cfb8265 100644
--- a/lib/compiler/src/beam_utils.erl
+++ b/lib/compiler/src/beam_utils.erl
@@ -1004,47 +1004,52 @@ live_opt([{recv_mark,_}=I|Is], Regs, D, Acc) ->
live_opt([], _, _, Acc) -> Acc.
-live_opt_block([{set,Ds,Ss,Op0}|Is], Regs0, D, Acc) ->
- Regs1 = x_live(Ss, x_dead(Ds, Regs0)),
- {Op, Regs} = live_opt_block_op(Op0, Regs1, D),
- I = {set, Ds, Ss, Op},
-
- case Ds of
- [{x,X}] ->
- case (not is_live(X, Regs0)) andalso Op =:= move of
- true ->
- live_opt_block(Is, Regs0, D, Acc);
- false ->
- live_opt_block(Is, Regs, D, [I|Acc])
- end;
- _ ->
- live_opt_block(Is, Regs, D, [I|Acc])
+live_opt_block([{set,[{x,X}]=Ds,Ss,move}=I|Is], Regs0, D, Acc) ->
+ Regs = x_live(Ss, x_dead(Ds, Regs0)),
+ case is_live(X, Regs0) of
+ true ->
+ live_opt_block(Is, Regs, D, [I|Acc]);
+ false ->
+ %% Useless move, will never be used.
+ live_opt_block(Is, Regs, D, Acc)
end;
-live_opt_block([{'%anno',_}|Is], Regs, D, Acc) ->
- live_opt_block(Is, Regs, D, Acc);
-live_opt_block([], Regs, _, Acc) -> {Acc,Regs}.
-
-live_opt_block_op({alloc,Live0,AllocOp}, Regs0, D) ->
- Regs =
- case AllocOp of
- {Kind, _N, Fail} when Kind =:= gc_bif; Kind =:= put_map ->
- live_join_label(Fail, D, Regs0);
- _ ->
- Regs0
- end,
+live_opt_block([{set,Ds,Ss,{alloc,Live0,AllocOp}}|Is], Regs0, D, Acc) ->
+ %% Calculate liveness from the point of view of the GC.
+ %% There will never be a GC if the instruction fails, so we should
+ %% ignore the failure branch.
+ GcRegs1 = x_dead(Ds, Regs0),
+ GcRegs = x_live(Ss, GcRegs1),
+ Live = live_regs(GcRegs),
%% The life-time analysis used by the code generator is sometimes too
%% conservative, so it may be possible to lower the number of live
%% registers based on the exact liveness information. The main benefit is
%% that more optimizations that depend on liveness information (such as the
- %% beam_bool and beam_dead passes) may be applied.
- Live = live_regs(Regs),
- true = Live =< Live0,
- {{alloc,Live,AllocOp}, live_call(Live)};
-live_opt_block_op({bif,_N,Fail} = Op, Regs, D) ->
- {Op, live_join_label(Fail, D, Regs)};
-live_opt_block_op(Op, Regs, _D) ->
- {Op, Regs}.
+ %% beam_dead pass) may be applied.
+ true = Live =< Live0, %Assertion.
+ I = {set,Ds,Ss,{alloc,Live,AllocOp}},
+
+ %% Calculate liveness from the point of view of the preceding instruction.
+ %% The liveness is the union of live registers in the GC and the live
+ %% registers at the failure label.
+ Regs1 = live_call(Live),
+ Regs = live_join_alloc(AllocOp, D, Regs1),
+ live_opt_block(Is, Regs, D, [I|Acc]);
+live_opt_block([{set,Ds,Ss,{bif,_,Fail}}=I|Is], Regs0, D, Acc) ->
+ Regs1 = x_dead(Ds, Regs0),
+ Regs2 = x_live(Ss, Regs1),
+ Regs = live_join_label(Fail, D, Regs2),
+ live_opt_block(Is, Regs, D, [I|Acc]);
+live_opt_block([{set,Ds,Ss,_}=I|Is], Regs0, D, Acc) ->
+ Regs = x_live(Ss, x_dead(Ds, Regs0)),
+ live_opt_block(Is, Regs, D, [I|Acc]);
+live_opt_block([{'%anno',_}|Is], Regs, D, Acc) ->
+ live_opt_block(Is, Regs, D, Acc);
+live_opt_block([], Regs, _, Acc) -> {Acc,Regs}.
+
+live_join_alloc({Kind,_Name,Fail}, D, Regs) when Kind =:= gc_bif; Kind =:= put_map ->
+ live_join_label(Fail, D, Regs);
+live_join_alloc(_, _, Regs) -> Regs.
live_join_labels([{f,L}|T], D, Regs0) when L =/= 0 ->
Regs = gb_trees:get(L, D) bor Regs0,