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

[Matt Arsenault 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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arsenm wrote:

I don't understand how this improves the situation, or how the IR can "understand the ABI". The IR has its own ABI. This may or may not match the C ABI, the IR ABI is not really defined in terms of C 

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