Meghana Gupta 586de0af75 Fix KnownSafety optimization bugs in ARCSequenceOpts ...

While doing bottom up dataflow, if we encounter an
unmatched retain instruction, that can pair with a 'KnownSafe'
already visited release instruction, we turn off KnownSafety if the two
RCIdentities mayAlias.
This is done in BottomUpRefCountState::checkAndResetKnownSafety.
In order to determine if a retain is umatched, we look at
IncToDecStateMap. If a retain was matched during bottom up dataflow, it
is always found in IncToDecStateMap with value of the matched release's
BottomUpRefCountState.

Similarly, during top down dataflow, if we encounter an unmatched
release instruction, that can pair with a 'KnownSafe' already
visited retain instruction, we turn off KnownSafety if the two RCIdentities
mayAlias.
This is done in TopDownRefCountState::checkAndResetKnownSafety.
In order to determine if a release is umatched, we look at
DecToIncStateMap. If a release was matched during top down dataflow, it
is always found in DecToIncStateMap with value of the matched retain's
TopDownRefCountState.

For ARCLoopOpts, during bottom up and top down traversal of a region with
a nested loop, we find if the retain/release in the loop summary was
matched or not by looking at the persistent RefCountInstToMatched map.
This map is populated when processing the nested loop region from the
IncToDecStateMap/DecToStateMap which gets thrown away after the loop
region is processed.

This fixes the bugs in both ARCSequenceOpts without loop
support and with loop support.

2020-09-03 00:51:19 -07:00

10 KiB

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