Stack underflow when `if` used in `raise`

Assessment

Research direction

Description

// run in fsi
open System

let repro (b: bool) = Math.Max (1, raise (Exception (if b then "x" else "y")))

let control (b: bool) = Math.Max (1, String.length (if b then "x" else "y"))

try control true |> ignore; printfn "control: ok" with ex -> printfn "control: %s" (ex.GetType().Name)
try repro true |> ignore; printfn "repro: ok" with ex -> printfn "repro: %s" (ex.GetType().Name)

try
    ...
with ...  ->
    return raise (SerializationException (if data.Length > 0 then int data.[0] else 0, "index out of range"))

control: ok
repro: ok

control: ok
System.InvalidProgramException: Common Language Runtime detected an invalid program.

IL_0000: ldc.i4.1
IL_0001: ldc.i4.0
IL_0002: brfalse.s    IL_000c
IL_0004: ldnull
IL_0005: unbox.any    [System.Runtime]System.Int32
IL_000a: br.s         IL_0033
IL_000c: stloc.0      // V_0
IL_000d: stloc.1      // V_1 <- saves a second value, but only one is on the stack -> underflow

Contributor guide

Open the contributing guide

First steps

1. Read the whole issue, then the project's contributing guide.
2. Comment on the issue to say you are picking it up — it saves two people doing the same work.
3. Fork the repository and make your change on a branch.
4. Open a pull request that references the issue number.

More from dotnet/fsharp

• Semantic classification cache for opened documents is never populated (written to the unopened-documents cache) Open
  Needs-Triage

  Difficulty 1/5 Under an hour Newbie friendliness 90/100

  dotnet/fsharp#20445 · Opened Sep 3, 2026

• F# compiler internal error FS0073 when merging duplicate property accessors for interface/class property implementation Open
  Needs-Triage

  Difficulty 2/5 1-3 hours Newbie friendliness 78/100

  dotnet/fsharp#20265 · 1 comment · Opened Aug 15, 2026

• Filtered try/with in seq { } emits int 0 where seq<'T> is expected for the unmatched case Open
  Bug Needs-Triage

  Difficulty 2/5 1-3 hours Newbie friendliness 78/100

  dotnet/fsharp#20040 · Opened Jul 7, 2026

• Rename accepts `_` as a new name for a value that is used Open
  Needs-Triage

  Difficulty 3/5 1-2 days Newbie friendliness 68/100

  dotnet/fsharp#20597 · Opened Sep 20, 2026

• The vsintegration cancellableTask computation expression cannot bind ValueTask Open
  Needs-Triage

  Difficulty 5/5 Over a week Newbie friendliness 48/100

  dotnet/fsharp#20596 · Opened Sep 20, 2026

All issues in dotnet/fsharp

Similar issues

• `XmlField.find` reads attributes by position and always wraps in `Optional.of`, so a missing `access` child shifts every later attribute Open
  bug

  Difficulty 2/5 1-3 hours Newbie friendliness 76/100

  objectionary/jeo-maven-plugin#1758 · Opened Sep 20, 2026

• [mlir][docs] Toy tutorial Ch.6 sample output is stale and can't be reproduced Open
  mlir

  Difficulty 2/5 1-3 hours Newbie friendliness 84/100

  llvm/llvm-project#224908 · 1 comment · Opened Sep 20, 2026

• `min` and `max` error for mixed `Signed` and `Unsigned` arguments Open

  Difficulty 2/5 1-3 hours Newbie friendliness 75/100

  JuliaLang/julia#63286 · Opened Sep 19, 2026

• JIT: vpshufbitqmb is missing INS_FLAGS_IsDstDstSrcAVXInstruction Open
  area-CodeGen-coreclr untriaged

  Difficulty 1/5 Under an hour Newbie friendliness 92/100

  dotnet/runtime#134286 · 1 comment · Opened Sep 19, 2026

• Preprocessor reports false "Invalid number literal: exponent has no digits" for hex literals such as `0x9E` Open

  Difficulty 2/5 1-3 hours Newbie friendliness 88/100

  secondlife/sl-vscode-plugin#147 · Opened Sep 19, 2026

More Compilers issues