[llvm] [GlobalISel] Add `GITypeOf` special type (PR #66079)

[Pierre van Houtryve via llvm-commits]

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@@ -101,6 +101,48 @@ pattern, you can try naming your patterns to see exactly where the issue is.
   // using $x again here copies operand 1 from G_AND into the new inst.
   (apply (COPY $root, $x))
 
+Types
+-----
+
+ValueType
+~~~~~~~~~
+
+Subclasses of ``ValueType`` are valid types, e.g. ``i32``.
+
+GITypeOf
+~~~~~~~~
+
+``GITypeOf<"$x">`` is a ``GISpecialType`` that allows for the creation of a
+register or immediate with the same type as another (register) operand.
+
+Operand:
+
+* An operand name as a string, prefixed by ``$``.
+
+Semantics:
+
+* Can only appear in an 'apply' pattern.
+* The operand name used must appear in the 'match' pattern of the
+  same ``GICombineRule``.
+
+.. code-block:: text
+  :caption: Example: Immediate
+
+  def mul_by_neg_one: GICombineRule <
+    (defs root:$root),
+    (match (G_MUL $dst, $x, -1)),
+    (apply (G_SUB $dst, (GITypeOf<"$x"> 0), $x))
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Pierre-vh wrote:

I got some inference working, see #66377 so the TypeOf in this case is removed.

https://github.com/llvm/llvm-project/pull/66079