[clang] [llvm] [RISCV][MC] Support experimental Zilx extension (PR #209419)

[Jessica Clarke via cfe-commits]

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@@ -0,0 +1,34 @@
+# RUN: not llvm-mc -triple=riscv32 --mattr=+experimental-zilx %s 2>&1 \
+# RUN:        | FileCheck %s --check-prefixes=CHECK-ERROR,CHECK-RV32-ERROR
+# RUN: not llvm-mc -triple=riscv64 --mattr=+experimental-zilx %s 2>&1 \
+# RUN:        | FileCheck %s --check-prefix=CHECK-ERROR
+
+# Zilx loads take three registers; the memory-operand syntax is not accepted.
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jrtc27 wrote:

Pre/post-increment should probably be part of the mnemonic, and I think it would be odd to not have `a(b)` work for reg+reg.

Whatever we do though, please let it not be the AArch64 approach where you have to look carefully at commas and whether there's an `!` hiding at the end (that some syntax highlighting will believe is the start of a comment, thanks to that being SPARC's line comment character).

https://github.com/llvm/llvm-project/pull/209419