alloca cause DMD compiler error (Internal error: eh.c 54)

[Maxime Chevalier-Boisvert]

I'm getting a strange compiler error when using alloca in my 
code. What's doubly strange is that I have 2 functions in the 
same file needing to call alloca for the same purpose. It seems 
to work fine in one of the functions, but uncommenting alloca in 
the other causes this cryptic error message to appear:

Internal error: eh.c 54
I believe it might be because the problematic function also 
creates structs on the stack. The following minimal example 
replicates the compiler error:

struct TheStruct
{
    ~this()
    {
    }
}

void bar()
{
}

void foo(IRInstr instr)
{
    auto s = TheStruct();

    bar();

    auto a = alloca(16);
}