ICE on struct nested inside a delegate passed to template

[JohanEngelen]

Testcase:

import std.traits;

void acceptDelegate(void delegate())
{
}

void bug()
{
    acceptDelegate({
        struct T
        {
        }

        bool b = __traits(compiles, fullyQualifiedName!T);
    });
}

ldc2 testcase.d results in:

Assertion failed: (!isaStruct(t)), function DtoBitCast, file ../gen/tollvm.cpp, line 533.
0  ldc2                     0x000000010927e5e8 llvm::sys::PrintStackTrace(llvm::raw_ostream&) + 40
1  ldc2                     0x000000010927ec76 SignalHandler(int) + 422
2  libsystem_platform.dylib 0x00007fff5bf3cf5a _sigtramp + 26
3  ldc2                     0x000000010a6d0728 gIR + 0
4  libsystem_c.dylib        0x00007fff5bcda1ae abort + 127
5  libsystem_c.dylib        0x00007fff5bca21ac basename_r + 0
6  ldc2                     0x0000000107378762 DtoBitCast(llvm::Value*, llvm::Type*, llvm::Twine const&) + 322
7  ldc2                     0x00000001073614c5 DtoCallFunction(Loc&, Type*, DValue*, Array<Expression*>*, llvm::Value*) + 2853
8  ldc2                     0x00000001073675b5 ToElemVisitor::call(IRState*, CallExp*, llvm::Value*) + 1157
9  ldc2                     0x000000010736c0a4 ToElemVisitor::visit(CallExp*) + 20
10 ldc2                     0x0000000107366c2a toElemDtor(Expression*) + 106
11 ldc2                     0x000000010735c569 ToIRVisitor::visit(ExpStatement*) + 329
12 ldc2                     0x000000010735c6e1 ToIRVisitor::visit(CompoundStatement*) + 289
13 ldc2                     0x0000000107355e85 Statement_toIR(Statement*, IRState*) + 37
14 ldc2                     0x000000010731a103 DtoDefineFunction(FuncDeclaration*, bool) + 5907
15 ldc2                     0x00000001072fefef Declaration_codegen(Dsymbol*) + 47
16 ldc2                     0x000000010732c826 codegenModule(IRState*, Module*) + 3382
17 ldc2                     0x00000001073b38aa ldc::CodeGenerator::emit(Module*) + 202
18 ldc2                     0x00000001073ce400 codegenModules(Array<Module*>&) + 272
19 ldc2                     0x00000001071633be mars_mainBody(Param&, Array<char const*>&, Array<char const*>&) + 5838

I've tried to minimize it further by copying the fullyQualifiedName source into the testcase, but that breaks it somehow.

[kinke]

Compiles 'fine' without assertions, glad you have them enabled. :) Sry, mixed things up - compiles fine for Win64, asserts (or crashes with disabled assertions) for Linux x64.

Works when making the lambda a delegate (not function) literal.

[kinke]

Argh...

acceptDelegate(delegate() { ... }) => works
acceptDelegate(function() { ... }) => error: cannot pass function arg to delegate param
acceptDelegate(() { ... }) => ICE
bool b; acceptDelegate(() { ... b = ...; }); => works

=> probably to be fixed in frontend

[kinke]

This would seemingly patch over the cracks on our end:

diff --git a/gen/toir.cpp b/gen/toir.cpp
index 23244cf36..8b17020b2 100644
--- a/gen/toir.cpp
+++ b/gen/toir.cpp
@@ -2183,13 +2183,15 @@ public:

     genFuncLiteral(fd, e);

-    if (fd->isNested()) {
+    if (e->type->toBasetype()->ty == Tdelegate) {
       LLType *dgty = DtoType(e->type);

-      LLValue *cval;
+      LLValue *cval = getNullPtr(getVoidPtrType());
       auto &funcGen = p->funcGen();
       auto &irfn = funcGen.irFunc;
-      if (funcGen.nestedVar && fd->toParent2() == irfn.decl) {
+      if (!fd->isNested()) {
+        // null context is fine
+      } else if (funcGen.nestedVar && fd->toParent2() == irfn.decl) {
         // We check fd->toParent2() because a frame allocated in one
         // function cannot be used for a delegate created in another
         // function. Happens with anonymous functions.
@@ -2198,16 +2200,12 @@ public:
         cval = irfn.nestArg;
       } else if (irfn.thisArg) {
         AggregateDeclaration *ad = irfn.decl->isMember2();
-        if (!ad || !ad->vthis) {
-          cval = getNullPtr(getVoidPtrType());
-        } else {
+        if (ad && ad->vthis) {
           cval =
               ad->isClassDeclaration() ? DtoLoad(irfn.thisArg) : irfn.thisArg;
           cval = DtoLoad(
               DtoGEP(cval, 0, getFieldGEPIndex(ad, ad->vthis), ".vthis"));
         }
-      } else {
-        cval = getNullPtr(getVoidPtrType());
       }
       cval = DtoBitCast(cval, dgty->getContainedType(0));

but the proper fix would probably be in the frontend (as it apparently requires some special __traits(compiles, ...) case).

[JohanEngelen]

Compiles 'fine' without assertions, glad you have them enabled. :)

Unfortunately I did not have assertions enabled on the machine that initially compiled the bigger code, and it crashed inside LLVM SelectionDAG. It took a while for me to find that LDC was generating bad IR (still shouldn't have crashed LLVM, but OK).

Not sure if it needs to be fixed in the frontend. Is the AST semi-invalid? DMD seems to have no problem with the testcase.

[JohanEngelen]

Works when making the lambda a delegate (not function) literal.

This is strange to me. Is there a difference between a lambda and a delegate literal? Perhaps indicating a frontend bug?

[kinke]

The sheer fact that the lambda apparently needs some special speculative context to fail like this, i.e., have an erroneous effect on its FuncLiteralDeclaration.isNested() (wrongly false), is IMO a clear indication.

It could also be related to

ldc/gen/toir.cpp

Lines 2148 to 2155 in bdb613d

	if ((fd->tok == TOKreserved || fd->tok == TOKdelegate) &&
	(e && e->type->ty == Tpointer)) {
	// This is a lambda that was inferred to be a function literal instead
	// of a delegate, so set tok here in order to get correct types/mangling.
	// Horrible hack, but DMD does the same thing.
	fd->tok = TOKfunction;
	fd->vthis = nullptr;
	}

That code wasn't hit by the testcase, but still. I checked DMD, these TOK.reserved hacks are still in place (and the testcase's FuncExp.tok was TOK.reserved).