[SILGen] Remove subtle identity function call. #67846
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Way back in commit d0bb027 Author: Joe Groff <[email protected]> Date: Mon Nov 23 11:47:09 2015 -0800 the convention was changed such that LValues were passed only by box rather than by box and address. Delete the comment that says that both are passed.
Back in 33f4f57 of swiftlang#28044 fame, non-`CaptureKind::Constant:` uses of `Entry.val` in `SILGenFunction::emitCaptures` were replaced with a use of the newly added lambda `getAddressValue` applied at `Entry.val`. The replacement of `Entry.value` with `getAddressValue(Entry.value)` in the case of `CaptureKind::Box` had no effect. Back then, the reason was that the condition SGM.Types .getTypeLowering( valueType, TypeExpansionContext::noOpaqueTypeArchetypesSubstitution( expansion.getResilienceExpansion())) .isAddressOnly() && !entryValue->getType().isAddress() under which something other than the input was returned would never hold: CaptureKind::Box is used for LValues and those never satisfy `!entryValue->getType().isAddress()`. Since that PR, the getAddressValue lambda has grown. There are two additional aspects to consider: (1) forceCopy, (2) isPack. (1) is not relevant because `false` was being passed for the `CaptureKind::Box` case. (2) can not currently happen because pack lvalues haven't been implemented. But even if they were implemented, the argument passed to the lambda would still need to be an address. The same all holds for the `CaptureKind::ImmutableBox` case which only differs from the `CaptureKind::Box` by a couple of lines.
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@swift-ci please test |
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@swift-ci please test source compatibility |
slavapestov
approved these changes
Aug 10, 2023
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Back in 33f4f57 of #28044 fame, non-
CaptureKind::Constant:uses ofEntry.valinSILGenFunction::emitCaptureswere replaced with a use of the newly added lambdagetAddressValueapplied atEntry.val.The replacement of
Entry.valuewithgetAddressValue(Entry.value)in the case ofCaptureKind::Boxhad no effect.Back then, the reason was that the condition
under which something other than the input was returned would never hold:
CaptureKind::Boxis used for LValues and those never satisfy!entryValue->getType().isAddress().Since that PR, the
getAddressValuelambda has grown. There are two additional aspects to consider: (1)forceCopy, (2)isPack. (1) is not relevant becausefalsewas being passed for theCaptureKind::Boxcase. (2) can not currently happen because pack lvalues haven't been implemented. But even if they were implemented, the argument passed to the lambda would still need to be an address, and it still wouldn't be desired to convert that address (a project_box) into an on-stack temporary (what theisPackbranch ofgetAddressValuepresently does).The same all holds for the
CaptureKind::ImmutableBoxcase which only differs from theCaptureKind::Boxby a couple of lines.