[clang] [Clang] Add elementwise conversions from encoded FP8 values (PR #212647)

[Chinmay Deshpande via cfe-commits]

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@@ -0,0 +1,172 @@
+// NOTE: Assertions have been autogenerated by utils/update_cc_test_checks.py UTC_ARGS: --version 6
+// RUN: %clang_cc1 -triple x86_64-unknown-linux-gnu -emit-llvm -o - %s | FileCheck %s
+
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chinmaydd wrote:

> The error should be either shown in a test or (better) clang should handle this case for better ergonomics.

Agreed. Integer constants that fit in 8 bits are now accepted. Negative, out-of-range, and non-constant ints still error. 

> Additionally, do we expect std::byte be a valid input to the builtin? Same Q for struct bit fields.

`std::byte` is now accepted. Bit-fields are accepted only if the declared type is 8-bit such as `unsigned char x : 8`.

Tests added for all of the new cases.

https://github.com/llvm/llvm-project/pull/212647