[clang] [llvm] [X86] Support EGPR for inline assembly. (PR #92338)

[Shengchen Kan via llvm-commits]

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@@ -5418,6 +5418,8 @@ X86:
   operand will get allocated only to RAX -- if two 32-bit operands are needed,
   you're better off splitting it yourself, before passing it to the asm
   statement.
+- ``jR``: An 8, 16, 32, or 64-bit integer EGPR when EGPR feature is on.
+  Otherwise, same as ``R``.
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KanRobert wrote:

I think it's same as `r` instead of `R` if egpr is off. Could I know why we design it as  `jR` instead of `jr`?

https://github.com/llvm/llvm-project/pull/92338