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authorBjörn Gustavsson <[email protected]>2018-11-01 11:58:07 +0100
committerBjörn Gustavsson <[email protected]>2018-11-06 10:16:54 +0100
commitae481c6c374f4e54b6cad44aea02322c23e105b5 (patch)
treea99e7838628864e6e04dd07ae6dba790e703b686 /lib/compiler
parent1565b1518f77b2c078c59c2554305b7dca668f72 (diff)
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beam_trim: Recognize more safe labels
Recognize more safe labels to enable stack trimming in more circumstances.
Diffstat (limited to 'lib/compiler')
-rw-r--r--lib/compiler/src/beam_trim.erl57
1 files changed, 44 insertions, 13 deletions
diff --git a/lib/compiler/src/beam_trim.erl b/lib/compiler/src/beam_trim.erl
index c11ecab927..f8efc38d53 100644
--- a/lib/compiler/src/beam_trim.erl
+++ b/lib/compiler/src/beam_trim.erl
@@ -21,7 +21,7 @@
-module(beam_trim).
-export([module/2]).
--import(lists, [member/2,reverse/1,reverse/2,splitwith/2,sort/1]).
+-import(lists, [any/2,member/2,reverse/1,reverse/2,splitwith/2,sort/1]).
-record(st,
{safe :: cerl_sets:set(beam_asm:label()) %Safe labels.
@@ -221,22 +221,53 @@ remap_block([{set,Ds0,Ss0,Info}|Is], Map, Acc) ->
Ss = [Map(S) || S <- Ss0],
remap_block(Is, Map, [{set,Ds,Ss,Info}|Acc]);
remap_block([], _, Acc) -> reverse(Acc).
-
-safe_labels([{label,L},{line,_},{badmatch,{Tag,_}}|Is], Acc) when Tag =/= y ->
- safe_labels(Is, [L|Acc]);
-safe_labels([{label,L},{line,_},{case_end,{Tag,_}}|Is], Acc) when Tag =/= y ->
- safe_labels(Is, [L|Acc]);
-safe_labels([{label,L},{line,_},if_end|Is], Acc) ->
- safe_labels(Is, [L|Acc]);
-safe_labels([{label,L},
- {block,[{set,[{x,0}],[{Tag,_}],move}]},
- {line,_},
- {call_ext,1,{extfunc,erlang,error,1}}|Is], Acc) when Tag =/= y ->
- safe_labels(Is, [L|Acc]);
+
+%% safe_labels([Instruction], Accumulator) -> gb_set()
+%% Build a gb_set of safe labels. The code at a safe
+%% label does not depend on the values in a specific
+%% Y register, only that all Y registers are initialized
+%% so that it safe to scan the stack when an exception
+%% is generated.
+%%
+%% In other words, code at a safe label will continue
+%% to work if Y registers have been renumbered and
+%% the size of the stack frame has changed.
+
+safe_labels([{label,L}|Is], Acc) ->
+ case is_safe_label(Is) of
+ true -> safe_labels(Is, [L|Acc]);
+ false -> safe_labels(Is, Acc)
+ end;
safe_labels([_|Is], Acc) ->
safe_labels(Is, Acc);
safe_labels([], Acc) -> cerl_sets:from_list(Acc).
+is_safe_label([{line,_}|Is]) ->
+ is_safe_label(Is);
+is_safe_label([{badmatch,{Tag,_}}|_]) ->
+ Tag =/= y;
+is_safe_label([{case_end,{Tag,_}}|_]) ->
+ Tag =/= y;
+is_safe_label([{try_case_end,{Tag,_}}|_]) ->
+ Tag =/= y;
+is_safe_label([if_end|_]) ->
+ true;
+is_safe_label([{block,Bl}|Is]) ->
+ is_safe_label_block(Bl) andalso is_safe_label(Is);
+is_safe_label([{call_ext,_,{extfunc,M,F,A}}|_]) ->
+ erl_bifs:is_exit_bif(M, F, A);
+is_safe_label(_) -> false.
+
+is_safe_label_block([{set,Ds,Ss,_}|Is]) ->
+ IsYreg = fun({y,_}) -> true;
+ (_) -> false
+ end,
+ %% This instruction is safe if the instruction
+ %% neither reads or writes Y registers.
+ not (any(IsYreg, Ss) orelse any(IsYreg, Ds)) andalso
+ is_safe_label_block(Is);
+is_safe_label_block([]) -> true.
+
%% frame_layout([Instruction], [{kill,_}], St) ->
%% [{kill,Reg} | {live,Reg} | {dead,Reg}]
%% Figure out the layout of the stack frame.