IR: fixes for subscript accessors (#322)

* IR: fixes for subscript accessors

Fixes #320

This is a bunch of fixes for handling of `__subscript` operations on builtin types (notably `RWStructuredBuffer` and `StructuredBuffer` at this point).

- Automatically add a `GetterDecl` to any subscript decalratio was declithout any accessors. This avoids hitting a null- dereference in the emit logic.

- Add a notion of a `RefAccessor` (declared with `ref`) as a peer to getters and setters. The idea is that a `ref` accessor returns a pointer to the element data, so that it can be used for both getting and setting values. This is closer to the behavior of `RWStructuredBuffer` element access in HLSL.

- Fixes for dealing with "access chains" where there might be a combination of a subscript (where the is a `get` and `set` but no `ref`) and member access, so that we have to read the base value into a temp, modify it, and then write it back.
  - This logic is still a bit of a mess, so we will eventually want to take a more consistent pass over this to deal with how we "materialize" values for setters.

- Update `RWStructuredBuffer` to have a `ref` accessor, and then fix up the IR tests to handle the new opcode that I added for it.
  - Note: I didn't handle this as an intrinsic simply because the `tests/ir/*` tests aren't really set up to handle builtins with ugly mangled names.

* Fixup: type error in VM for buffer element ref

I was using the result type of the op as the element type for computing the element address, but the result type is a pointer to the real element type.
This caused test failures on 64-bit platforms, where the stride of the buffer in the `ir/factorial` test needs to be 4.

The fix is to assume the result type is a pointer, and extract the pointed-to type out of that.

1 files changed, 30 insertions, 0 deletions

diff --git a/source/slang/check.cpp b/source/slang/check.cpp
index 4840ae30d..b981fb778 100644
--- a/source/slang/check.cpp
+++ b/source/slang/check.cpp
@@ -3575,6 +3575,32 @@ namespace Slang
 
             decl->SetCheckState(DeclCheckState::CheckedHeader);
 
+            // If we have a subscript declaration with no accessor declarations,
+            // then we should create a single `GetterDecl` to represent
+            // the implicit meaning of their declaration, so:
+            //
+            //      subscript(uint index) -> T;
+            //
+            // becomes:
+            //
+            //      subscript(uint index) -> T { get; }
+            //
+
+            bool anyAccessors = false;
+            for(auto accessorDecl : decl->getMembersOfType<AccessorDecl>())
+            {
+                anyAccessors = true;
+            }
+
+            if(!anyAccessors)
+            {
+                RefPtr<GetterDecl> getterDecl = new GetterDecl();
+                getterDecl->loc = decl->loc;
+
+                getterDecl->ParentDecl = decl;
+                decl->Members.Add(getterDecl);
+            }
+
             for(auto mm : decl->Members)
             {
                 checkDecl(mm);
@@ -4662,6 +4688,10 @@ namespace Slang
                             {
                                 callExpr->type.IsLeftValue = true;
                             }
+                            for(auto refAccessor : subscriptDeclRef.getDecl()->getMembersOfType<RefAccessorDecl>())
+                            {
+                                callExpr->type.IsLeftValue = true;
+                            }
                         }
 
                         // TODO: there may be other cases that confer l-value-ness