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authorBjörn Gustavsson <[email protected]>2016-05-23 20:13:48 +0200
committerBjörn Gustavsson <[email protected]>2016-05-30 13:19:20 +0200
commitb1b27719d713c0e62d3242bbf1da0600ea0a651f (patch)
tree7376b00ada2e29bae532bd997a2a02fecec1faf6 /lib
parent88632d70cc866b5e54589ccb9311c7c5a88ecb46 (diff)
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Eliminate unsafe use of Y registers
If the Core Erlang optimization were turned off (using no_copt), the optimization passes for Beam assembly could generate unsafe code that did not initialize all Y registers before (for example) a call instruction. To fix this, beam_dead should not attempt to remove stores to Y registers. That is not safe if there is an exception-generating instruction inside a try...catch block.
Diffstat (limited to 'lib')
-rw-r--r--lib/compiler/src/beam_dead.erl18
-rw-r--r--lib/compiler/test/beam_utils_SUITE.erl45
2 files changed, 59 insertions, 4 deletions
diff --git a/lib/compiler/src/beam_dead.erl b/lib/compiler/src/beam_dead.erl
index dd42add433..b01f58f683 100644
--- a/lib/compiler/src/beam_dead.erl
+++ b/lib/compiler/src/beam_dead.erl
@@ -262,7 +262,7 @@ backward([{select,select_val,Reg,{f,Fail0},List0}|Is], D, Acc) ->
backward([{jump,{f,To0}},{move,Src,Reg}=Move|Is], D, Acc) ->
To = shortcut_select_label(To0, Reg, Src, D),
Jump = {jump,{f,To}},
- case beam_utils:is_killed_at(Reg, To, D) of
+ case is_killed_at(Reg, To, D) of
false -> backward([Move|Is], D, [Jump|Acc]);
true -> backward([Jump|Is], D, Acc)
end;
@@ -420,7 +420,7 @@ comp_op_find_shortcut(To0, Reg, Val, D) ->
To0 ->
not_possible();
To ->
- case beam_utils:is_killed_at(Reg, To, D) of
+ case is_killed_at(Reg, To, D) of
false -> not_possible();
true -> To
end
@@ -863,3 +863,17 @@ get_literal(nil) ->
get_literal({literal,_}=Lit) ->
Lit;
get_literal({_,_}) -> error.
+
+
+%%%
+%%% Removing stores to Y registers is not always safe
+%%% if there is an instruction that causes an exception
+%%% within a catch. In practice, there are few or no
+%%% opportunities for removing stores to Y registers anyway
+%%% if sys_core_fold has been run.
+%%%
+
+is_killed_at({x,_}=Reg, Lbl, D) ->
+ beam_utils:is_killed_at(Reg, Lbl, D);
+is_killed_at({y,_}, _, _) ->
+ false.
diff --git a/lib/compiler/test/beam_utils_SUITE.erl b/lib/compiler/test/beam_utils_SUITE.erl
index ae813d563b..f6d4a311bb 100644
--- a/lib/compiler/test/beam_utils_SUITE.erl
+++ b/lib/compiler/test/beam_utils_SUITE.erl
@@ -23,7 +23,8 @@
init_per_group/2,end_per_group/2,
apply_fun/1,apply_mf/1,bs_init/1,bs_save/1,
is_not_killed/1,is_not_used_at/1,
- select/1,y_catch/1,otp_8949_b/1,liveopt/1,coverage/1]).
+ select/1,y_catch/1,otp_8949_b/1,liveopt/1,coverage/1,
+ y_registers/1]).
-export([id/1]).
suite() -> [{ct_hooks,[ts_install_cth]}].
@@ -44,7 +45,8 @@ groups() ->
y_catch,
otp_8949_b,
liveopt,
- coverage
+ coverage,
+ y_registers
]}].
init_per_suite(Config) ->
@@ -311,6 +313,45 @@ clinic(Damage) ->
end,
carefully.
+y_registers(_Config) ->
+ {'EXIT',{{badfun,0},_}} = (catch economic(0.0, jim)),
+ {'EXIT',{{badmatch,apartments},_}} = (catch louisiana()),
+ {a,b} = (boxes(true))({a,b}),
+ {'EXIT',{{case_clause,webmaster},_}} = (catch yellow(true)),
+ ok.
+
+economic(0.0 = Serves, Existence) ->
+ case Serves of
+ Serves -> 0
+ end,
+ Existence = jim,
+ 0(),
+ Serves,
+ Existence.
+
+louisiana() ->
+ {catch necessarily,
+ try
+ [] == reg,
+ true = apartments
+ catch [] -> barbara
+ end}.
+
+boxes(Call) ->
+ case Call of
+ Call -> approval
+ end,
+ Call,
+ fun id/1.
+
+yellow(Hill) ->
+ case webmaster of
+ station -> eyes; Hill ->
+ "under"
+ end,
+ Hill,
+ id(42).
+
%% The identity function.
id(I) -> I.