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-rw-r--r--lib/compiler/src/beam_bool.erl41
1 files changed, 31 insertions, 10 deletions
diff --git a/lib/compiler/src/beam_bool.erl b/lib/compiler/src/beam_bool.erl
index d9ea6f5a70..81be262d6d 100644
--- a/lib/compiler/src/beam_bool.erl
+++ b/lib/compiler/src/beam_bool.erl
@@ -168,18 +168,18 @@ bopt_block(Reg, Fail, OldIs, [{block,Bl0}|Acc0], St0) ->
end.
%% ensure_opt_safe(OriginalCode, OptCode, FollowingCode, Fail,
-%% ReversedPreceedingCode, State) -> ok
+%% ReversedPrecedingCode, State) -> ok
%% Comparing the original code to the optimized code, determine
%% whether the optimized code is guaranteed to work in the same
%% way as the original code.
%%
%% Throw an exception if the optimization is not safe.
%%
-ensure_opt_safe(Bl, NewCode, OldIs, Fail, PreceedingCode, St) ->
+ensure_opt_safe(Bl, NewCode, OldIs, Fail, PrecedingCode, St) ->
%% Here are the conditions that must be true for the
%% optimization to be safe.
%%
- %% 1. If a register is INITIALIZED by PreceedingCode,
+ %% 1. If a register is INITIALIZED by PrecedingCode,
%% then if that register assigned a value in the original
%% code, but not in the optimized code, it must be UNUSED or KILLED
%% in the code that follows.
@@ -190,29 +190,50 @@ ensure_opt_safe(Bl, NewCode, OldIs, Fail, PreceedingCode, St) ->
%% by the code that follows.
%%
%% 3. Any register that is assigned a value in the optimized
- %% code must be UNUSED or KILLED in the following code
- %% (because the register might be assigned the wrong value,
- %% and even if the value is right it might no longer be
- %% assigned on *all* paths leading to its use).
+ %% code must be UNUSED or KILLED in the following code,
+ %% unless we can be sure that it is always assigned the same
+ %% value.
- InitInPreceeding = initialized_regs(PreceedingCode),
+ InitInPreceding = initialized_regs(PrecedingCode),
PrevDst = dst_regs(Bl),
NewDst = dst_regs(NewCode),
NotSet = ordsets:subtract(PrevDst, NewDst),
- MustBeKilled = ordsets:subtract(NotSet, InitInPreceeding),
- MustBeUnused = ordsets:subtract(ordsets:union(NotSet, NewDst), MustBeKilled),
+ MustBeKilled = ordsets:subtract(NotSet, InitInPreceding),
case all_killed(MustBeKilled, OldIs, Fail, St) of
false -> throw(all_registers_not_killed);
true -> ok
end,
+ Same = assigned_same_value(Bl, NewCode),
+ MustBeUnused = ordsets:subtract(ordsets:union(NotSet, NewDst),
+ ordsets:union(MustBeKilled, Same)),
case none_used(MustBeUnused, OldIs, Fail, St) of
false -> throw(registers_used);
true -> ok
end,
ok.
+%% assigned_same_value(OldCode, NewCodeReversed) -> [DestinationRegs]
+%% Return an ordset with a list of all y registers that are always
+%% assigned the same value in the old and new code. Currently, we
+%% are very conservative in that we only consider identical move
+%% instructions in the same order.
+%%
+assigned_same_value(Old, New) ->
+ case reverse(New) of
+ [{block,Bl}|_] ->
+ assigned_same_value(Old, Bl, []);
+ _ ->
+ ordsets:new()
+ end.
+
+assigned_same_value([{set,[{y,_}=D],[S],move}|T1],
+ [{set,[{y,_}=D],[S],move}|T2], Acc) ->
+ assigned_same_value(T1, T2, [D|Acc]);
+assigned_same_value(_, _, Acc) ->
+ ordsets:from_list(Acc).
+
update_fail_label([{set,_,_,move}=I|Is], Fail, Acc) ->
update_fail_label(Is, Fail, [I|Acc]);
update_fail_label([{set,Ds,As,{bif,N,{f,_}}}|Is], Fail, Acc) ->