[silgen] When transforming values into an existential box representat… #17088
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…ion, do it at +1. In general, SILGen assumes that only +1 values are "forwarded" into memory. This is because we want any value that is stored in memory to not be dependent on other values and for the forwarded object to be able to maintain its own liveness. So this assert was correct to fire. The specific test case that exposed this issue is: What happened here is that we needed to reabstract a loadable value into an existential and tried to maximally abstract it and thus store it into memory. The That code was never updated to make sure the value was at +1. So we would store a guaranteed value into memory and hope that whereever we stored it doesn't escape the current function. In this case, I believe that we would be safe... but past returns are not indicators of future results. rdar://40773543 SR-7858 (cherry picked from commit d2e1bcd)
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…ion, do it at +1.
In general, SILGen assumes that only +1 values are "forwarded" into memory. This
is because we want any value that is stored in memory to not be dependent on
other values and for the forwarded object to be able to maintain its own
liveness. So this assert was correct to fire.
The specific test case that exposed this issue is:
What happened here is that we needed to reabstract a loadable value into an
existential and tried to maximally abstract it and thus store it into
memory. The That code was never updated to make sure the value was at +1. So we
would store a guaranteed value into memory and hope that whereever we stored it
doesn't escape the current function. In this case, I believe that we would be
safe... but past returns are not indicators of future results.
rdar://40773543
SR-7858
(cherry picked from commit d2e1bcd)