Internal Compiler error: calling method that modifies const object

[tex3d]

Related to #4340.

// RUN: %dxc -T vs_6_0 %s | FileCheck %s

// Internal Compiler error: llvm::cast<X>() argument of incompatible type!

struct MyStruct {
    int Idx;
    void Set() {
        Idx = 1;
    }
} Obj;

void main()
{
    Obj.Set();
}

[llvm-beanz]

Godbolt link: https://godbolt.org/z/adMedG6xc

[llvm-beanz]

This requires a language change to get right because HLSL's overload resolution doesn't handle const-ness of the implicit object.

[llvm-beanz]

Linking the language spec proposal: https://github.com/microsoft/hlsl-specs/blob/main/proposals/0007-const-instance-methods.md