[llvm] [AMDGPU] Add AMDGPU specific variadic operation MCExprs (PR #82022)

[Matt Arsenault via llvm-commits]

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@@ -1512,6 +1512,24 @@ The AMDGPU backend supports the following calling conventions:
 
      =============================== ==========================================================
 
+AMDGPU MCExpr
+-------------
+
+As part of the AMDGPU MC layer, AMDGPU provides the following target specific
+``MCExpr``\s.
+
+  .. table:: AMDGPU MCExpr types:
+     :name: amdgpu-mcexpr-table
+
+     =================== ======================================================================
+     AMDGPU MCExpr       Description
+     =================== ======================================================================
+     ``max(arg, ...)``   Variadic operation that returns maximum value of all its arguments.
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arsenm wrote:

Specify it's signed 

https://github.com/llvm/llvm-project/pull/82022