6283 – [CTFE][Regression 2.054] Failed to assign to AA using a constness-changed array as key

Test case:
-----------------------------------
static assert( {
 immutable qq = "qq";
 string q = qq; // <-- from immutable(char[]) to immutable(char)[]
 int[string] pieces = ["a":1];
 pieces[q] = 0; // <-- can't interpret
 return true;
}() );
-----------------------------------
x.d(9): Error: cannot evaluate delegate pure nothrow bool()
{
immutable immutable(char[]) qq = "qq";
string q = qq;
int[string] pieces = ["a":1];
pieces[q] = 0;
return true;
}
() at compile time
x.d(1): Error: static assert (delegate pure nothrow bool()
{
immutable immutable(char[]) qq = "qq";
string q = qq;
int[string] pieces = ["a":1];
pieces[q] = 0;
return true;
}
()) is not evaluatable at compile time
-----------------------------------

The regression was introduced in commit 08352 in fixing the type-painting bug revealed by bug 4063.
https://github.com/D-Programming-Language/dmd/commit/08352 

https://github.com/D-Programming-Language/dmd/commit/3309fcddfbc4e445a3e418c31a49d157c33161aa
https://github.com/D-Programming-Language/dmd/commit/2ea02077de9498746f5abb0043dc6ae1e5accefc 

Not yet fixed in these 2 slight variants:
Test case 2:
-----------------------------------
static assert({
 immutable p = "pp";
 int[string] pieces = [p: 0];
 pieces["qq"] = 1;
 return true;
}());
-----------------------------------
x.d(6): Error: cannot evaluate delegate pure nothrow bool()
....
-----------------------------------
Test case 3:
-----------------------------------
static assert({
 immutable renames = [0: "pp"];
 int[string] pieces;
 pieces[true ? renames[0] : "qq"] = 1;
 pieces["anything"] = 1;
 return true;
}());
-----------------------------------
x.d(7): Error: cannot evaluate delegate pure nothrow bool()
....
-----------------------------------

(In reply to comment #3)
> Not yet fixed in these 2 slight variants:
> 
[snip]
... and the cause of these 2 variants are the same: Equals() in constfold.c cannot handle (e1->op == TOKslice && e2->op == TOKstring).

https://github.com/D-Programming-Language/dmd/commit/0904c8aa200e4d080d500d96d5904c33ba17cc86
https://github.com/D-Programming-Language/dmd/commit/e48a8c67f02172c72e04f36759d2d6868d716368