[all-commits] [llvm/llvm-project] fb2823: [AArch64][llvm] Tighten SYSP; don't disassemble in...

[Jonathan Thackray via All-commits]

  Branch: refs/heads/users/jthackray/tighten_sysp_encoding
  Home:   https://github.com/llvm/llvm-project
  Commit: fb282368ee943ac249cc5966d48ee1c6d29f9080
      https://github.com/llvm/llvm-project/commit/fb282368ee943ac249cc5966d48ee1c6d29f9080
  Author: Jonathan Thackray <jonathan.thackray at arm.com>
  Date:   2026-02-20 (Fri, 20 Feb 2026)

  Changed paths:
    M llvm/lib/Target/AArch64/AArch64InstrFormats.td
    M llvm/lib/Target/AArch64/AArch64InstrInfo.td
    M llvm/lib/Target/AArch64/Disassembler/AArch64Disassembler.cpp
    M llvm/lib/Target/AArch64/MCTargetDesc/AArch64InstPrinter.cpp
    M llvm/test/MC/AArch64/armv9-sysp-diagnostics.s
    M llvm/test/MC/AArch64/armv9a-sysp.s

  Log Message:
  -----------
  [AArch64][llvm] Tighten SYSP; don't disassemble invalid encodings

Tighten SYSP aliases, so that invalid encodings are disassembled
to `<unknown>`. This is because:

```
  Cn is a 4-bit unsigned immediate, in the range 8 to 9
  Cm is a 4-bit unsigned immediate, in the range 0 to 7
  op1 is a 3-bit unsigned immediate, in the range 0 to 6
  op2 is a 3-bit unsigned immediate, in the range 0 to 7
```

Ensure we check this when disassembling, and also constrain
tablegen for compile-time errors of invalid encodings.

Also adjust the testcases in `armv9-sysp-diagnostics.s` and
`llvm/test/MC/AArch64/armv9a-sysp.s` as they were invalid,
and added a few invalid (outside of range) SYSP-alikes to
test that `<unknown>` is printed



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