[clang] [llvm] target ABI: improve call parameters extensions handling (PR #100757)

[Nikita Popov via cfe-commits]

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@@ -1185,6 +1189,9 @@ Currently, only the following parameter attributes are defined:
     value should be sign-extended to the extent required by the target's
     ABI (which is usually 32-bits) by the caller (for a parameter) or
     the callee (for a return value).
+``noext`` This indicates to the code generator that the parameter or return
+    value has the high bits undefined, as for a struct in register, and
+    therefore does not need to be sign or zero extended.
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nikic wrote:

The description here should say that this is the same as the default behavior, but some targets have additional validation to make sure one of the attributes is always present.

https://github.com/llvm/llvm-project/pull/100757