diff options
Diffstat (limited to 'lib/compiler/src/beam_block.erl')
| -rw-r--r-- | lib/compiler/src/beam_block.erl | 17 |
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 |