[5.0] Fix SILCombine to devirtualize existentials wrapped in enum. #21239
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This allows Swift code to implement a fast path via a protocol type
check as follows:
if let existentialVal = genericVal as? SomeProtocol {
// do something fast.
}
Fixes <rdar://problem/46322928> Failure to devirtualize a protocol
method applied to an opened existential blocks implemention of
DataProtocol.
Note: the approach of devirtualization via backward pattern matching
is fundamentally wrong and will never be fully general. It should be a
forward type propagation.
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@swift-ci test. |
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@swift-ci test source compatibility. |
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--- CCC --- Explanation: Fix SILCombine to devirtualize Optional existentials. This blocks the addition of DataProtocol which is an ABI change. Scope: Only affects -O builds. Extends an existing optimization to recognize more complex SIL patterns. Issue: rdar://problem/46322928 Failure to devirtualize a protocol method applied to an opened existential blocks implemention of DataProtocol. Risk: Medium. This adds a conservative pattern match to SILCombine. The biggest risk is that performing more optimization exposes some other bug in the optimizer. Testing: New unit tests tests were added in both .swift and .sil. |
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@eeckstein please review for CCC. I won't merge it until 5.0 branch is ready for PRs. |
| SILValue swift::getAddressOfStackInit(AllocStackInst *ASI, | ||
| /// | ||
| /// allocStackAddr may either itself be an AllocStackInst or an | ||
| /// InitEnumDataAddrInst that projects the value of an AllocStackInst. |
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It would make sense to turn this comment into an assert.
|
@swift-ci test source compatibility. |
This allows Swift code to implement a fast path via a protocol type
check as follows:
if let existentialVal = genericVal as? SomeProtocol {
// do something fast.
}
Fixes rdar://problem/46322928 Failure to devirtualize a protocol
method applied to an opened existential blocks implemention of
DataProtocol.
Note: the approach of devirtualization via backward pattern matching
is fundamentally wrong and will never be fully general. It should be a
forward type propagation.