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author | Björn Gustavsson <[email protected]> | 2010-10-12 10:08:18 +0200 |
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committer | Björn Gustavsson <[email protected]> | 2010-10-12 14:15:36 +0200 |
commit | f6a2fb81fd87e671ceed85261a1c28a6082f010c (patch) | |
tree | faf8abfab935ac33adcb3fece584fd6d1017a341 /lib/erl_interface/include/ei_connect.h | |
parent | 499082d25170aa7edf922a6aee0465a7ffb144d4 (diff) | |
download | otp-f6a2fb81fd87e671ceed85261a1c28a6082f010c.tar.gz otp-f6a2fb81fd87e671ceed85261a1c28a6082f010c.tar.bz2 otp-f6a2fb81fd87e671ceed85261a1c28a6082f010c.zip |
beam_block: Do optimizations in the safe order
Moving of allocation instructions upwards in the instruction
stream (in order to enable further optimizations) in beam_block,
is implemented with the assumption that if a register {x,X}
contains a valid term, then all other x register with lower
numbers than X also contain valid terms. That assumption is
true after code generation.
The beam_utils:live_opt/1 optimization, however, may invalidate
that assumption. For instance, if a receive statement exports a
variable that is used, but the return value of the receive statement
is not used, then {x,1} but not {x,0} contains a valid term at the
end of the receive statement. If the receive statement is
followed by
{bif,self,{f,0},[],{x,0}}.
{test_heap,NumberOfWords,2}.
moving the allocation upwards will produce
{test_heap,NumberOfWords,2}.
{bif,self,{f,0},[],{x,0}}.
which will cause the beam_validator pass to scream loudly that
{x,0} is not live at the test_heap instruction.
Fix the problem by doing the optimizations in reverse order.
Reported-by: Jim Engquist
Diffstat (limited to 'lib/erl_interface/include/ei_connect.h')
0 files changed, 0 insertions, 0 deletions