[clang] [llvm] [IR][HLSL] Add llvm.structured.gep instruction (PR #176145)

[Sebastian Neubauer via cfe-commits]

Nathan =?utf-8?q?Gauër?= <brioche at google.com>,
Nathan =?utf-8?q?Gauër?= <brioche at google.com>
Message-ID:
In-Reply-To: <llvm.org/llvm/llvm-project/pull/176145 at github.com>


================
@@ -14991,6 +14991,188 @@ Semantics:
 
 See the description for :ref:`llvm.stacksave <int_stacksave>`.
 
+.. _i_structured_gep:
+
+'``llvm.structured.gep``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+      declare <ret_type>
+      @llvm.structured.gep(ptr elementtype(<basetype>) <source>
+                           {, [i32/i64] <index> }*)
+
+Overview:
+"""""""""
+
+The '``llvm.structured.gep``' intrinsic (structured **G**\ et\ **E**\ lement\ **P**\ tr) computes a new pointer address
+resulting of a logical indexing into the ``<source>`` pointer. The returned
+address depends on the indices and may depend on the layout of %basetype at
+runtime.
+
+Arguments:
+""""""""""
+
+``<ty> basetype``:
+The actual value passed is ignored, and should be ``poison``.
+
+``ptr <source>``:
+A pointer to a memory location assumed to hold a completely laid out value
+with the same type as ``basetype``. The physical layout of ``basetype`` is
+target dependent, and is not always known at compile time.
+The assumption this instruction makes on the memory location is only relevant
+to this particular call. A frontend could possibly emit multiple structured
+GEP with the same source pointer but a different ``basetype``.
+
+The ``source`` argument must be annotated with an :ref:`elementtype
+<attr_elementtype>` attribute at the call-site. This attribute specifies the
+type of the element pointed by the pointer source. This type will be
+used along with the provided indices and source operands to compute a new
+pointer representing the result of a logical indexing into a basetype
+pointed by source.
+
+``[i32/i64] index, ...``:
+Indices used to traverse into the basetype and determine the target element
+this instruction computes an offset for. Indices can be 32-bit or 64-bit
----------------
Flakebi wrote:

Hm, maybe we can find something clearer here than target element and offset.
structured.gep doesn’t really compute an offset but a new pointer.

Maybe this?
```
Indices used to traverse into the basetype and compute a pointer to the target element.
```

https://github.com/llvm/llvm-project/pull/176145