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, 2 insertions, 0 deletions

diff --git a/source/slang/emit.cpp b/source/slang/emit.cpp
index 311f903cc..5cd0ea832 100644
--- a/source/slang/emit.cpp
+++ b/source/slang/emit.cpp
@@ -4875,6 +4875,7 @@ emitDeclImpl(decl, nullptr);
         case kIROp_FieldAddress:
         case kIROp_getElementPtr:
         case kIROp_specialize:
+        case kIROp_BufferElementRef:
             return true;
         }
 
@@ -5516,6 +5517,7 @@ emitDeclImpl(decl, nullptr);
             break;
 
         case kIROp_BufferLoad:
+        case kIROp_BufferElementRef:
             emitIROperand(ctx, inst->getArg(0));
             emit("[");
             emitIROperand(ctx, inst->getArg(1));