Nathan =?utf-8?q?Gauër?= <[email protected]>,
Nathan =?utf-8?q?Gauër?= <[email protected]>
Message-ID:
In-Reply-To: <llvm.org/llvm/llvm-project/pull/[email protected]>
================
@@ -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
+unsigned integers. Indices being handled one by one, both sizes can be mixed
+in the same instruction. The precision used to compute the resulting pointer
+is target-dependent.
+When used to index into a struct, only integer constants are allowed.
+
+Semantics:
+""""""""""
+
+The ``llvm.structured.gep`` performs a logical traversal of the type
+``basetype`` using the list of provided indices, computing the pointer
+addressing the targeted element/field assuming ``source`` points to a
+physically laid out ``basetype``.
+
+The first index determines which element/field of ``basetype`` is selected,
+computes the pointer to access this element/field assuming ``source`` points
+to the start of ``basetype``.
+This pointer becomes the new ``source``, the current type the new
+``basetype``, and the next indices is consumed until a scalar type is
+reached or all indices are consumed.
+
+All indices must be consumed, and it is illegal to index into a scalar type.
+Meaning the maximum number of indices depends on the depth of the basetype.
+
+Because this instruction performs a logical addressing, all indices are
+assumed to be inbounds. This means it is not possible to access the next
+element in the logical layout by overflowing:
+
+- If the indexed type is a struct with N fields, the index must be an
+ immediate/constant value in the range ``[0; N[``.
+- If indexing into an array or vector, the index can be a variable, but
+ assumed to be inbounds with regards to the current basetype logical layout.
----------------
Flakebi wrote:
but assumed → but **is** assumed?
https://github.com/llvm/llvm-project/pull/176145
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