Segfault on Compilation of Tuple of Unions

[SeanTAllen]

primitive Add
primitive Dec
type AddOrDec is (Add | Dec)
type CmRDTCounterOp is (AddOrDec, U128)

class CmRDTCounter
  var _value: U128

  new create() => _value = 0

  fun read(): U128 =>
    _value

  fun ref add(number: U128): CmRDTCounterOp =>
    let op: CmRDTCounterOp =
      if number >= 0 then
        (Add, number)
      else
        (Dec, number)
      end
    apply(op)
    op

  fun ref apply(op: CmRDTCounterOp) =>
    match op
      | (Add, let number: U128) => _value = _value + number
      | (Dec, let number: U128) => _value = _value - number
    end

actor Main
  new create(env: Env) =>
    var counter = CmRDTCounter.create()
    let op1 = counter.add(10)

The last line causes the segfault. Remove it and all is good.

I built using latest master. LLVM 3.9.1. OSX.

Was first reported by omarkj on IRC.

Backtrace under LLDB:

* thread #1: tid = 0x1a9dea, 0x0000000100b8509f ponyc`llvm::Value::setNameImpl(llvm::Twine const&) + 31, queue = 'com.apple.main-thread', stop reason = EXC_BAD_ACCESS (code=1, address=0x0)
  * frame #0: 0x0000000100b8509f ponyc`llvm::Value::setNameImpl(llvm::Twine const&) + 31
    frame #1: 0x0000000100b8533c ponyc`llvm::Value::setName(llvm::Twine const&) + 14
    frame #2: 0x0000000100836cfc ponyc`llvm::ExtractValueInst::Create(llvm::Value*, llvm::ArrayRef<unsigned int>, llvm::Twine const&, llvm::Instruction*) + 140
    frame #3: 0x0000000100b22809 ponyc`llvm::IRBuilder<llvm::ConstantFolder, llvm::IRBuilderDefaultInserter>::CreateExtractValue(llvm::Value*, llvm::ArrayRef<unsigned int>, llvm::Twine const&) + 89
    frame #4: 0x0000000100b227a9 ponyc`LLVMBuildExtractValue + 49
    frame #5: 0x0000000100c3dd08 ponyc`gen_assign_cast + 936
    frame #6: 0x0000000100c423db ponyc`assign_rvalue + 651
    frame #7: 0x0000000100c3a504 ponyc`gen_expr + 12676
    frame #8: 0x0000000100c38eb8 ponyc`gen_expr + 6968
    frame #9: 0x0000000100c55f4a ponyc`gentypes + 28794
    frame #10: 0x0000000100c31ac4 ponyc`codegen + 12164
    frame #11: 0x0000000100c047c4 ponyc`main + 6548
    frame #12: 0x00007fff9f1645ad libdyld.dylib`start + 1
    frame #13: 0x00007fff9f1645ad libdyld.dylib`start + 1

[omarkj]

Compiler details:

0.10.0 [release]
compiled with: llvm 3.9.0 -- Apple LLVM version 8.0.0 (clang-800.0.42.1)

I also ran this against current ponyc master (c223fc4). Backtrace under LLDB with that build:

* thread #1: tid = 0x2e1058, 0x0000000101843dd6 libsystem_kernel.dylib`__pthread_kill + 10, queue = 'com.apple.main-thread', stop reason = signal SIGABRT
  * frame #0: 0x0000000101843dd6 libsystem_kernel.dylib`__pthread_kill + 10
    frame #1: 0x000000010199a787 libsystem_pthread.dylib`pthread_kill + 90
    frame #2: 0x0000000100b959fd ponyc`abort + 14
    frame #3: 0x0000000100b959ef ponyc`__assert_rtn + 81
    frame #4: 0x000000010004517e ponyc`gen_assign_cast(c=0x00007fff5fbff350, l_type=0x000000010b800d30, r_value=0x0000000101d05e78, type=0x000000011122f380) + 526 at genexpr.c:287
    frame #5: 0x000000010003986a ponyc`gen_call(c=0x00007fff5fbff350, ast=0x000000011122da80) + 2778 at gencall.c:687
    frame #6: 0x00000001000448db ponyc`gen_expr(c=0x00007fff5fbff350, ast=0x000000011122da80) + 379 at genexpr.c:80
    frame #7: 0x000000010003c304 ponyc`gen_seq(c=0x00007fff5fbff350, ast=0x000000011121a280) + 84 at gencontrol.c:19
    frame #8: 0x00000001000447d9 ponyc`gen_expr(c=0x00007fff5fbff350, ast=0x000000011121a280) + 121 at genexpr.c:25
    frame #9: 0x0000000100046a05 ponyc`genfun_fun(c=0x00007fff5fbff350, t=0x0000000111231800, m=0x0000000111231b00) + 293 at genfun.c:298
    frame #10: 0x0000000100045dc9 ponyc`genfun_method_bodies(c=0x00007fff5fbff350, t=0x0000000111231800) + 441 at genfun.c:706
    frame #11: 0x0000000100066cee ponyc`gentypes(c=0x00007fff5fbff350) + 846 at gentype.c:779
    frame #12: 0x0000000100043824 ponyc`genexe(c=0x00007fff5fbff350, program=0x000000010afdf000) + 484 at genexe.c:434
    frame #13: 0x000000010003582a ponyc`codegen(program=0x000000010afdf000, opt=0x00007fff5fbff778) + 234 at codegen.c:904
    frame #14: 0x0000000100091213 ponyc`generate_passes(program=0x000000010afdf000, options=0x00007fff5fbff778) + 51 at pass.c:291
    frame #15: 0x0000000100001791 ponyc`compile_package(path=".", opt=0x00007fff5fbff778, print_program_ast=false, print_package_ast=false) + 161 at main.c:247
    frame #16: 0x0000000100001548 ponyc`main(argc=1, argv=0x00007fff5fbff828) + 1112 at main.c:370
    frame #17: 0x0000000101695255 libdyld.dylib`start + 1
    frame #18: 0x0000000101695255 libdyld.dylib`start + 1

Additionally, that compiler returns some more information during the fault:

Building builtin -> /Users/omarkj/code/ponyc/packages/builtin
Building . -> /Users/omarkj/code/bogi/src
Generating
 Reachability
 Selector painting
 Data prototypes
 Data types
 Function prototypes
 Functions
Assertion failed: (LLVMGetTypeKind(LLVMTypeOf(r_value)) == LLVMStructTypeKind), function gen_assign_cast, file src/libponyc/codegen/genexpr.c, line 287.

[omarkj]

Hey,

Been looking into this issue some more, and have narrowed it down to the return from the if statement which is bound using let. If I instead write this code things compile:

  fun ref makeOperation(number: U128) =>
    if number >= 0 then
      apply((Add, number))
    else
      apply((Dec, number))
    end

To get the other path (that is, returning from the if statement, binding it and passing it to another function) working I need to handle the impossible case that the if statement does not return by wrapping the return in a Maybe and guard against it later:

First I added these types:

primitive Nothing is Stringable
  fun string(): String iso^ => "Nothing".string()
type Maybe[A] is (Nothing | A)

And then rewrite the logic this way:

  fun ref maybeMakeAndApplyOperation(number: U128): Maybe[U128] =>
    let maybeOp =
      if number >= 0 then
        (Add, number)
      else
        (Dec, number)
      end
    maybeApply(maybeOp)

  fun ref maybeApply(op: Maybe[CmRDTCounterOp]): Maybe[U128] =>
    match op
      | Nothing => Nothing
      | (let o: CmRDTCounterOp) => _apply(o)
    else
      Nothing
    end

This compiles and runs as expected.

[omarkj]

I've been looking into this a little bit, and isolated this to the primitive that's in
the boxed type. gen_unbox in genbox.c on line 45 returns the unchanged object if
t->primitive is NULL which happens to be the case here.

Is probably related to the reachability ds, similar to #1474.

[SeanTAllen]

@omarkj awesome digging

[Praetonus]

This probably is another case of the general issue with tuples not having a type descriptor.

[SeanTAllen]

@sylvanc doesn't believe this is tuples related. going to be looking at it. i'm leaving the needs discussion during sync tag so we revisit next week.

[SeanTAllen]

This now errors at:

src/libponyc/codegen/genexpr.c:306: gen_assign_cast: Assertion `LLVMGetTypeKind(LLVMTypeOf(r_value)) == LLVMStructTypeKind` failed.

Backtrace:
  0   ponyc                               0x000000010401f8d1 ponyint_assert_fail + 161
  1   ponyc                               0x0000000103f8750f gen_assign_cast + 927
  2   ponyc                               0x0000000103f951d1 assign_rvalue + 801
  3   ponyc                               0x0000000103f94e34 gen_assign + 180
  4   ponyc                               0x0000000103f86994 gen_expr + 260
  5   ponyc                               0x0000000103f80a64 gen_seq + 68
  6   ponyc                               0x0000000103f86c42 gen_expr + 946
  7   ponyc                               0x0000000103f89901 genfun_method_bodies + 3153
  8   ponyc                               0x0000000103faca30 gentypes + 6464
  9   ponyc                               0x0000000103f86444 genexe + 596
  10  ponyc                               0x0000000103f78b57 codegen + 199
  11  ponyc                               0x0000000103f44a25 main + 1557
  12  libdyld.dylib                       0x00007fff93ae45ad start + 1

[SeanTAllen]

backtrace:

(lldb) bt
* thread #1: tid = 0x8836ee, 0x00007fff99300f06 libsystem_kernel.dylib`__pthread_kill + 10, queue = 'com.apple.main-thread', stop reason = signal SIGABRT
  * frame #0: 0x00007fff99300f06 libsystem_kernel.dylib`__pthread_kill + 10
    frame #1: 0x00007fff93c4a4ec libsystem_pthread.dylib`pthread_kill + 90
    frame #2: 0x00007fff98c166df libsystem_c.dylib`abort + 129
    frame #3: 0x00000001000fb223 ponyc`ponyint_assert_fail(expr="LLVMGetTypeKind(LLVMTypeOf(r_value)) == LLVMStructTypeKind", file="src/libponyc/codegen/genexpr.c", line=306, func="gen_assign_cast") + 403 at ponyassert.c:60
    frame #4: 0x000000010004afda ponyc`gen_assign_cast(c=0x00007fff5fbff268, l_type=0x000000010b803e10, r_value=0x000000010c204718, type=0x0000000108024700) + 634 at genexpr.c:306
    frame #5: 0x00000001000576a5 ponyc`assign_local(c=0x00007fff5fbff268, l_value=0x000000010c2047e8, r_value=0x000000010c204718, l_type=0x0000000108044080, r_type=0x0000000108024700) + 149 at genoperator.c:334
    frame #6: 0x0000000100057396 ponyc`assign_rvalue(c=0x00007fff5fbff268, left=0x0000000108025180, r_type=0x0000000108024700, r_value=0x000000010c204718) + 1174 at genoperator.c:519
    frame #7: 0x000000010005714c ponyc`assign_rvalue(c=0x00007fff5fbff268, left=0x0000000108054e40, r_type=0x0000000108024700, r_value=0x000000010c204718) + 588 at genoperator.c:445
    frame #8: 0x0000000100056eb3 ponyc`gen_assign(c=0x00007fff5fbff268, ast=0x0000000108057bc0) + 179 at genoperator.c:897
    frame #9: 0x000000010004a835 ponyc`gen_expr(c=0x00007fff5fbff268, ast=0x0000000108057bc0) + 821 at genexpr.c:144
    frame #10: 0x0000000100041c04 ponyc`gen_seq(c=0x00007fff5fbff268, ast=0x000000010804ecc0) + 84 at gencontrol.c:22
    frame #11: 0x000000010004a579 ponyc`gen_expr(c=0x00007fff5fbff268, ast=0x000000010804ecc0) + 121 at genexpr.c:25
    frame #12: 0x000000010004cda1 ponyc`genfun_fun(c=0x00007fff5fbff268, t=0x0000000107fe7200, m=0x0000000107fe5c00) + 529 at genfun.c:436
    frame #13: 0x000000010004c039 ponyc`genfun_method_bodies(c=0x00007fff5fbff268, t=0x0000000107fe7200) + 441 at genfun.c:895
    frame #14: 0x000000010007a943 ponyc`gentypes(c=0x00007fff5fbff268) + 979 at gentype.c:884
    frame #15: 0x0000000100049f68 ponyc`genexe(c=0x00007fff5fbff268, program=0x000000010afbfd40) + 504 at genexe.c:409
    frame #16: 0x0000000100039a42 ponyc`codegen(program=0x000000010afbfd40, opt=0x00007fff5fbff768) + 274 at codegen.c:1026
    frame #17: 0x00000001000a8dd3 ponyc`generate_passes(program=0x000000010afbfd40, options=0x00007fff5fbff768) + 51 at pass.c:301
    frame #18: 0x0000000100002691 ponyc`compile_package(path=".", opt=0x00007fff5fbff768, print_program_ast=false, print_package_ast=false) + 161 at main.c:255
    frame #19: 0x000000010000243a ponyc`main(argc=1, argv=0x00007fff5fbff818) + 1146 at main.c:395
    frame #20: 0x00007fff93ae45ad libdyld.dylib`start + 1
    frame #21: 0x00007fff93ae45ad libdyld.dylib`start + 1

[sylvanc]

@Praetonus was exactly right. It's a union of tuples vs tuples of unions problem.

[sylvanc]

On line 305 in genexpr.c, the compiler is expecting to find that the RHS is a boxed tuple type, since the LHS is a tuple type. Instead, it finds that the RHS is a union of two tuple types. As a result, the compiler has no c_t->primitive to unbox with. It's possible the right approach is to use the type descriptor in a boxed tuple to figure out how to unbox it.

[Praetonus]

Minimal case:

actor Main
  new create(env: Env) =>
    let a: ((Main, Env) | (Env, Main)) = (this, env)
    let b: ((Main | Env), (Main | Env)) = a