diff options
author | Björn Gustavsson <[email protected]> | 2016-05-13 15:59:31 +0200 |
---|---|---|
committer | Björn Gustavsson <[email protected]> | 2016-05-16 07:51:26 +0200 |
commit | 7f4f4ef02349b4bf973cbc3bacc4d53a6a6abad2 (patch) | |
tree | f1b894393bd7471edf8d486443cbaa98ced0d21e /lib/compiler/doc | |
parent | f679efe1c19cb7d6bab8a68226a9d748474ef902 (diff) | |
download | otp-7f4f4ef02349b4bf973cbc3bacc4d53a6a6abad2.tar.gz otp-7f4f4ef02349b4bf973cbc3bacc4d53a6a6abad2.tar.bz2 otp-7f4f4ef02349b4bf973cbc3bacc4d53a6a6abad2.zip |
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
Diffstat (limited to 'lib/compiler/doc')
0 files changed, 0 insertions, 0 deletions