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authorBjörn Gustavsson <bjorn@erlang.org>2016-05-13 15:59:31 +0200
committerBjörn Gustavsson <bjorn@erlang.org>2016-05-16 07:51:26 +0200
commit7f4f4ef02349b4bf973cbc3bacc4d53a6a6abad2 (patch)
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Eliminate crash in beam_bool
beam_bool would crash when attempting to optimize BEAM code similar to this code: bif '=:=' Reg1 SomeValue => y(0) bif '=:=' Reg2 {atom,true} => x(2) bif '=:=' Reg3 {atom,true} => x(3) bif 'or' x(2) x(3) => x(2) is_eq_exact Fail x(2) {atom,true} The problem is that the first instruction that assigns a value to a Y register. beam_bool:ssa_assign/2 will not accept a Y register argument. We could change ssa_assign/2 to accept a Y register, but that would only cause the entire optimization to be rejected later because the Y register is alive in the code that follows. Therefore, a better solution is to modify extend_block/3 so that the instruction that assign to Y registers are not added to the block. That is, the optimizer will only operate on the following code: bif '=:=' Reg2 {atom,true} => x(2) bif '=:=' Reg3 {atom,true} => x(3) bif 'or' x(2) x(3) => x(2) is_eq_exact Fail x(2) {atom,true} Usually the optimization will succeed, rewriting the four instructions to a select_val instruction. Assembly code such as the above can be produced by code similar to: Y = Something == SomethingElse, case Y of Condition; OtherCondition -> . . . end, . . ., Y. Reported-by: http://bugs.erlang.org/browse/ERL-143 Reported-by: José Valim
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