aboutsummaryrefslogtreecommitdiffstats
path: root/lib/compiler/src/beam_block.erl
diff options
context:
space:
mode:
authorBjörn Gustavsson <[email protected]>2016-05-31 22:49:42 +0200
committerBjörn Gustavsson <[email protected]>2016-06-01 10:09:20 +0200
commitaab1db16d0a732823fa9e2964c6a52b109c61742 (patch)
tree3ba6111af79e023fc1476dc815a14f9f95faa69a /lib/compiler/src/beam_block.erl
parentac927e00f82b3df962abe082393f45197de49156 (diff)
downloadotp-aab1db16d0a732823fa9e2964c6a52b109c61742.tar.gz
otp-aab1db16d0a732823fa9e2964c6a52b109c61742.tar.bz2
otp-aab1db16d0a732823fa9e2964c6a52b109c61742.zip
beam_block: Eliminate crash in beam_utils
Somewhat simplified, beam_block would rewrite the target for the first instruction in this code sequence: move x(0) => y(1) gc_bif '+' 1 x(0) => y(0) move y(1) => x(1) move nil => x(0) call 2 local_function/2 The resulting code would be: move x(0) => x(1) %% Changed target. gc_bif '+' 1 x(0) => y(0) move x(1) => y(1) %% Operands swapped (see 02d6135813). move nil => x(0) call 2 local_function/2 The resulting code is not safe because the x(1) will be killed by the gc_bif instruction. 7a47b20c3a cleaned up move optimizations and would reject the optimization if the target was an X register and an allocating instruction was found. To avoid this bug, the optimization must be rejected even if the target is a Y register.
Diffstat (limited to 'lib/compiler/src/beam_block.erl')
-rw-r--r--lib/compiler/src/beam_block.erl17
1 files changed, 11 insertions, 6 deletions
diff --git a/lib/compiler/src/beam_block.erl b/lib/compiler/src/beam_block.erl
index a8cfdffdf3..85d332c56e 100644
--- a/lib/compiler/src/beam_block.erl
+++ b/lib/compiler/src/beam_block.erl
@@ -262,12 +262,17 @@ opt_move_1(R, [{set,[D],[R],move}|Is0], Acc) ->
{yes,Is} -> opt_move_rev(D, Acc, Is);
no -> not_possible
end;
-opt_move_1({x,_}, [{set,_,_,{alloc,_,_}}|_], _) ->
- %% The optimization is not possible. If the X register is not
- %% killed by allocation, the optimization would not be safe.
- %% If the X register is killed, it means that there cannot
- %% follow a 'move' instruction with this X register as the
- %% source.
+opt_move_1(_R, [{set,_,_,{alloc,_,_}}|_], _) ->
+ %% The optimization is either not possible or not safe.
+ %%
+ %% If R is an X register killed by allocation, the optimization is
+ %% not safe. On the other hand, if the X register is killed, there
+ %% will not follow a 'move' instruction with this X register as
+ %% the source.
+ %%
+ %% If R is a Y register, the optimization is still not safe
+ %% because the new target register is an X register that cannot
+ %% safely pass the alloc instruction.
not_possible;
opt_move_1(R, [{set,_,_,_}=I|Is], Acc) ->
%% If the source register is either killed or used by this