Major Compile Performance Regression Swift 5.6


I'm posting this for greater visibility on this bug.

There seems to be a major compile speed regression when compiling postgres-nio using the latest Swift 5.6 Development toolchain.

I am seeing ~67 min compile time on M1 Max using the latest swift snapshot vs ~1 min with the Swift 5.5 release.

I have created issue SR-15531 on and issue 205 on

Snapshot: swift-DEVELOPMENT-SNAPSHOT-2022-01-09

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One small nit, that trunk snapshot from last weekend is no longer Swift 5.6, which branched last month, so trunk is now the basis of Swift 5.7 or 6.0 or whatever the next version will be numbered.

Do you see the same problem with the Swift 5.6 snapshots that were just released for the first time over the last couple days? Sometimes bugs go away in different branches, eg this armv7 compiler crasher I reported last month, which might help track down the cause.

@Buttaface yes the issue is present in main trunk snapshots since 2021-11-20

As further detail, this appears to be due to an upstream LLVM issue that is currently being isolated. The regression is believed to come from this LLVM commit.

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Note that the problem is not due to this commit. It is only exposed by it, but the problem is elsewhere.

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See [SR-15531] Major Compile Speed Regression when Compiling postgres-nio on Latest Swift Snapshot - Swift for the full story and the fix