[temp-rvalue-opt] Disable handling of load [take] in temp-rvalue-elim. #34327
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eeckstein
reviewed
Oct 16, 2020
eeckstein
reviewed
Oct 16, 2020
This pass was attempting to handle cases where we use load [take] + destroy_value instead of a destroy_addr since we have a loadable value. There are a few issues around how this was done, so for 5.3, we are just going to turn off the optimization. rdar://70356725
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tkremenek
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This pass was attempting to handle cases where we use load [take] +
destroy_value instead of a destroy_addr since we have a loadable value. There
are a few issues around how this was done, so for 5.3, we are just going to turn
off the optimization.
rdar://70356725
CCC
Explanation: This patch turns off an optimization in
TempRValueOpt that could cause miscompiles such as
leaks/use-after-frees. Note that we haven't seen this in practice
from actual Swift programs, we have only seen it in SIL code
snippets. So we are disabling this out of an abundance of
caution.
Scope: This miscompile could result in memory unsafety.
SR Issue: rdar://70356725
Risk: None. This is just turning off the optimization using a 2
line fix. We are going to do a fuller fix on main.
Testing: Added compiler tests that validate the optimization has
been disabled.
Reviewer: @eeckstein