diff options
| -rw-r--r-- | lib/compiler/src/beam_dead.erl | 22 |
1 files changed, 20 insertions, 2 deletions
diff --git a/lib/compiler/src/beam_dead.erl b/lib/compiler/src/beam_dead.erl index 3606af9d75..8ea949425e 100644 --- a/lib/compiler/src/beam_dead.erl +++ b/lib/compiler/src/beam_dead.erl @@ -266,12 +266,30 @@ backward([{jump,{f,To0}},{move,Src,Reg}=Move|Is], D, Acc) -> false -> backward([Move|Is], D, [Jump|Acc]); true -> backward([Jump|Is], D, Acc) end; -backward([{jump,{f,To}}=J|[{bif,Op,_,Ops,Reg}|Is]=Is0], D, Acc) -> +backward([{jump,{f,To}}=J|[{bif,Op,{f,BifFail},Ops,Reg}|Is]=Is0], D, Acc) -> try replace_comp_op(To, Reg, Op, Ops, D) of I -> backward(Is, D, I++Acc) catch - throw:not_possible -> backward(Is0, D, [J|Acc]) + throw:not_possible -> + case To =:= BifFail of + true -> + %% The bif instruction is redundant. See the comment + %% in the next clause for why there is no need to + %% test for liveness of Reg at label To. + backward([J|Is], D, Acc); + false -> + backward(Is0, D, [J|Acc]) + end end; +backward([{jump,{f,To}}=J|[{gc_bif,_,{f,To},_,_,_Dst}|Is]], D, Acc) -> + %% The gc_bif instruction is redundant, since either the gc_bif + %% instruction itself or the jump instruction will transfer control + %% to label To. Note that a gc_bif instruction does not assign its + %% destination register if the failure branch is taken; therefore, + %% the code at label To is not allowed to assume that the destination + %% register is initialized, and it is therefore no need to test + %% for liveness of the destination register at label To. + backward([J|Is], D, Acc); backward([{test,bs_start_match2,F,Live,[R,_]=Args,Ctxt}|Is], D, [{test,bs_match_string,F,[Ctxt,Bs]}, {test,bs_test_tail2,F,[Ctxt,0]}|Acc0]=Acc) -> |