From b1b27719d713c0e62d3242bbf1da0600ea0a651f Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?Bj=C3=B6rn=20Gustavsson?= Date: Mon, 23 May 2016 20:13:48 +0200 Subject: 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. --- lib/compiler/src/beam_dead.erl | 18 ++++++++++++++++-- 1 file changed, 16 insertions(+), 2 deletions(-) (limited to 'lib/compiler/src/beam_dead.erl') 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. -- cgit v1.2.3