aboutsummaryrefslogtreecommitdiffstats
path: root/lib/compiler/src
diff options
context:
space:
mode:
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/compiler/src
parent88632d70cc866b5e54589ccb9311c7c5a88ecb46 (diff)
downloadotp-b1b27719d713c0e62d3242bbf1da0600ea0a651f.tar.gz
otp-b1b27719d713c0e62d3242bbf1da0600ea0a651f.tar.bz2
otp-b1b27719d713c0e62d3242bbf1da0600ea0a651f.zip
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/compiler/src')
-rw-r--r--lib/compiler/src/beam_dead.erl18
1 files changed, 16 insertions, 2 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.