Assertion `hasValidInsertionPoint()' failed in variadic-generic function

[karwa]

Description

No response

Reproduction

@usableFromInline
enum SortOrder {
    case ascending
    case descending
}

@inlinable @inline(__always)
func isLessThan<Root, each Value: Comparable>(
    _ leftRoot: Root,
    _ rightRoot: Root,
    comparing properties: repeat ((Root) -> each Value, SortOrder)
) -> Bool {

    // Hopefully this will get constant-folded.
    var numProperties = 0
    for _ in repeat each properties {
        numProperties += 1
    }

    var propertyIdx = 0
    for (getProperty, mode) in repeat each properties {
        let (left, right) = (getProperty(leftRoot), getProperty(rightRoot))
        if propertyIdx < numProperties {
            guard left != right else { 
                propertyIdx += 1
                continue
            }
        }
        switch mode {
        case .ascending:  return left < right
        case .descending: return left > right
        }
    }
    return false
}

I built with -O, but with/without that flag, it seems to crash the compiler in the same spot.

Stack dump

swift-frontend: /home/build-user/swift/include/swift/SIL/SILBuilder.h:3024: void swift::SILBuilder::insertImpl(swift::SILInstruction *): Assertion `hasValidInsertionPoint()' failed.
Please submit a bug report (https://swift.org/contributing/#reporting-bugs) and include the crash backtrace.
Stack dump:
0.	Program arguments: /opt/compiler-explorer/swift-nightly/usr/bin/swift-frontend -frontend -S -primary-file <source> -target x86_64-unknown-linux-gnu -disable-objc-interop -g -debug-info-format=dwarf -dwarf-version=4 -O -empty-abi-descriptor -resource-dir /opt/compiler-explorer/swift-nightly/usr/lib/swift -Xllvm --x86-asm-syntax=intel -module-name output -plugin-path /opt/compiler-explorer/swift-nightly/usr/lib/swift/host/plugins -plugin-path /opt/compiler-explorer/swift-nightly/usr/local/lib/swift/host/plugins -enable-default-cmo -o /app/output.s
1.	Swift version 5.11-dev (LLVM 170b778140971f1, Swift 9b5da0d82fca791)
2.	Compiling with the current language version
3.	While evaluating request ASTLoweringRequest(Lowering AST to SIL for file "<source>")
4.	While silgen emitFunction SIL function "@$s6output10isLessThan__9comparingSbx_xq_xc_AA9SortOrderOtq_QptRv_SLR_r0_lF".
 for 'isLessThan(_:_:comparing:)' (at <source>:12:1)

Expected behavior

Describe the behavior you expected instead of the crash.

Err... no crash, of course :)

Environment

Swift version 5.11-dev (LLVM 170b778140971f1, Swift 9b5da0d)
Target: x86_64-unknown-linux-gnu

Additional information

No response

[karwa]

Seems to be related to the switch at the end of the loop body.

If I write it like this, it works:

@inlinable @inline(__always)
func isLessThan<Root, each Value: Comparable>(
    _ leftRoot: Root,
    _ rightRoot: Root,
    comparing properties: repeat ((Root) -> each Value, SortOrder)
) -> Bool {

    // This should get constant-folded.
    var numProperties = 0
    for _ in repeat each properties {
        numProperties += 1
    }

    var propertyIdx = 0
    for (getProperty, mode) in repeat each properties {
        let (left, right) = (getProperty(leftRoot), getProperty(rightRoot))
        // We can save an equality check for the final element.
        if propertyIdx < numProperties {
            guard left != right else { 
                propertyIdx += 1
                continue
            }
        }
        if mode == .ascending {
          return left < right
        } else if mode == .descending {
          // The 'if' condition on this branch is necessary to avoid a compiler crash.
          return left > right
        }
    }
    return false
}

The else condition needs to be else if mode == .descending (even though that's the only other case) in order to avoid the crash. A plain else makes it crash again.

[AnthonyLatsis]

Reduced test case:

func test<each T>(t: repeat each T) -> Bool {
  for _ in repeat each t {
    let _ = "Sima"
    return "fix" < "this"
  }

  return false
}

Describe the behavior you expected instead of the crash.

Err... no crash, of course :)

A compilation error is not a crash, but you expect this code to compile successfully, right? 🙂

---

cc @simanerush

[simanerush]

Thank you @AnthonyLatsis for reducing the test case!