Swift 6.0.x crash on win/arm64 Release build

[nil4]

Description

A compiler crash (assertion failure) occurs with swift build --configuration release on Windows ARM64. This is reproducible with Swift 6.0 and 6.0.1. With both Swift versions, the same code compiles without issue in debug configuration, or release on x64.

Summary of observed results:

Swift version	Architecture	Configuration	Result
6.0	arm64	release	💥 crash
6.0	arm64	debug	✅ works
6.0	x64	release	✅ works -- https://github.com/royalapplications/royalvnc/actions/runs/11513028067/job/32049003371#step:7:909
6.0.1	arm64	release	💥 crash
6.0.1	arm64	debug	✅ works
6.0.1	x64	release	✅ works -- https://github.com/royalapplications/royalvnc/actions/runs/11513740438/job/32051009618#step:7:910

Reproduction

Clone the repo and check out the relevant commit:

> git clone https://github.com/royalapplications/royalvnc.git
> cd royalvnc
> git reset aaca28ae04a93615489e3a6ab9f21b6f6bf51086 --hard

Run swift build and observe the debug build succeds:

> swift build
Building for debugging...
[<<< build output elided >>>]
Build complete! (73.07s)

Run swift build --configuration release and observe assertion failure and build crash:

> swift build --configuration release
Building for production...
error: compile command failed due to exception 3 (use -v to see invocation)
error: failed parsing the Swift compiler output: unexpected JSON message: {
  "exception" : 3,
  "kind" : "abnormal-exit",
  "name" : "compile",
  "output" : "Assertion failed: getAlign() && *getAlign() == Align && \"Alignment representation error!\", file C:\\Users\\swift-ci\\jenkins\\workspace\\swift-6.0.0-windows-toolchain-arm64\\llvm-project\\llvm\\lib\\IR\\Globals.cpp, line 140\r\nPlease submit a bug report (https:\/\/swift.org\/contributing\/#reporting-bugs) and include the crash backtrace.\r\nException Code: 0x80000003\r\nAssertion failed: getAlign() && *getAlign() == Align && \"Alignment representation error!\", file Rename failed: C:\\dev\\royalvnc\\.build\\aarch64-unknown-windows-msvc\\release\\RoyalVNCKit.build\\VNCRegion+CG.swift-fb46aa97.o.tmpC:\\Users\\swift-ci\\jenkins\\workspace\\swift-6.0.0-windows- -> toolchain-arm64\\llvm-project\\llvm\\lib\\IR\\Globals.cpp,C:\\dev\\royalvnc\\.build\\aarch64-unknown-windows-msvc\\release\\RoyalVNCKit.build\\VNCRegion+CG.swift.o line 140\r\n: permission denied\r\n",
  "pid" : 3180,
  "process" : {
    "real_pid" : 3180
  }
}: dataCorrupted(Swift.DecodingError.Context(codingPath: [CodingKeys(stringValue: "kind", intValue: nil)], debugDescription: "invalid kind", underlyingError: nil))

Stack dump

> swift build --configuration release
Building for production...
error: compile command failed due to exception 3 (use -v to see invocation)
error: failed parsing the Swift compiler output: unexpected JSON message: {
  "exception" : 3,
  "kind" : "abnormal-exit",
  "name" : "compile",
  "output" : "Assertion failed: getAlign() && *getAlign() == Align && \"Alignment representation error!\", file C:\\Users\\swift-ci\\jenkins\\workspace\\swift-6.0.0-windows-toolchain-arm64\\llvm-project\\llvm\\lib\\IR\\Globals.cpp, line 140\r\nPlease submit a bug report (https:\/\/swift.org\/contributing\/#reporting-bugs) and include the crash backtrace.\r\nException Code: 0x80000003\r\nAssertion failed: getAlign() && *getAlign() == Align && \"Alignment representation error!\", file Rename failed: C:\\dev\\royalvnc\\.build\\aarch64-unknown-windows-msvc\\release\\RoyalVNCKit.build\\VNCRegion+CG.swift-fb46aa97.o.tmpC:\\Users\\swift-ci\\jenkins\\workspace\\swift-6.0.0-windows- -> toolchain-arm64\\llvm-project\\llvm\\lib\\IR\\Globals.cpp,C:\\dev\\royalvnc\\.build\\aarch64-unknown-windows-msvc\\release\\RoyalVNCKit.build\\VNCRegion+CG.swift.o line 140\r\n: permission denied\r\n",
  "pid" : 3180,
  "process" : {
    "real_pid" : 3180
  }
}: dataCorrupted(Swift.DecodingError.Context(codingPath: [CodingKeys(stringValue: "kind", intValue: nil)], debugDescription: "invalid kind", underlyingError: nil))

Expected behavior

The assertion failure observed with arm64/release is unexpected. The build should work the same as arm64/debug locally, and x64/release on GitHub CI -- producing a compile error, or completing successfully.

Environment

> swiftc --version
Swift version 6.0.1 (swift-6.0.1-RELEASE)
Target: aarch64-unknown-windows-msvc

> ver
Microsoft Windows [Version 10.0.22621.4317]

Additional information

ref. royalapplications/royalvnc#11 (comment)

[nil4]

Repro steps updated and simplified -- involving only Swift tools.

[nil4]

Tested swiftc 6.0.2 and the issue is still reproducible.

[hjyamauchi]

I think this is caused by an MSVC arm64 miscompile issue that I reported here which was reported to MS and fixed here.

The upshot is that Visual Studio 17.9.x and 17.10.x (MSVC 14.39.x and 14.40.x, respecitively) compilers have an arm64 optimization bug and we need to use Visual Studio 17.8.x or earlier or 17.11.x or later to build the Windows/arm64 Swift toolchain to avoid this issue.

It appears that the swift.org CI is currently set up to use VS 17.9.x (MSVC 14.39.x). The latest release 6.0.3 still has the issue, unfortunately.