[llvm] [RISCV] Add missing assembler test case for c.addi zero, 0. NFC (PR #112291)

[Craig Topper via llvm-commits]

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@@ -147,6 +147,11 @@ c.sub a4, a5
 # CHECK-ASM: encoding: [0x01,0x00]
 # CHECK-NO-EXT:  error: instruction requires the following: 'C' (Compressed Instructions) or 'Zca' (part of the C extension, excluding compressed floating point loads/stores){{$}}
 c.nop
+# CHECK-ASM: c.addi zero, 0
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topperc wrote:

I know, but this syntax is supported by binutils. We have a internal tests from our hardware validation team that uses this syntax.

The isa-manual used to say "C.NOP is encoded as c.addi x0, 0 and so expands to addi x0, x0, 0. Breakpoint Instruction." but it was changed 6 years ago. https://github.com/riscv/riscv-isa-manual/pull/248

https://github.com/llvm/llvm-project/pull/112291