[RISCV] Correctly Decode Unsigned Immediates with Ranges (#128584)

We currently have two operands upstream that are an unsigned immediate
with a range constraint - `uimm8ge32` (for `cm.jalt`) and `uimm5gt3`
(for `qc.shladd`).

Both of these were using `decodeUImmOperand<N>` for decoding. For `Zcmt`
this worked, because the generated decoder automatically checked for
`cm.jt` first because the 8 undefined bits in `cm.jalt` are `000?????`
in `cm.jt` (this is to do with the range lower-bound being a
power-of-two). For Zcmt, this patch is NFC.

We have less luck with `Xqciac` - `qc.shladd` is being decoded where the
`uimm5` field is 3 or lower. This patch fixes this by introducing a
`decodeUImmOperandGE<Width, LowerBound>` helper, which will corretly
return `MCDisassembler::Fail` when the immediate is below the lower
bound.

I have added a test to show the encoding where `uimm5` is equal to 3 is
no longer disassembled as `qc.shladd`.

1 files changed, 13 insertions, 0 deletions

diff --git a/llvm/lib/Target/RISCV/Disassembler/RISCVDisassembler.cpp b/llvm/lib/Target/RISCV/Disassembler/RISCVDisassembler.cpp
index 8c07d87..830dc28 100644
--- a/llvm/lib/Target/RISCV/Disassembler/RISCVDisassembler.cpp
+++ b/llvm/lib/Target/RISCV/Disassembler/RISCVDisassembler.cpp
@@ -328,6 +328,19 @@ static DecodeStatus decodeUImmOperand(MCInst &Inst, uint32_t Imm,
   return MCDisassembler::Success;
 }
 
+template <unsigned Width, unsigned LowerBound>
+static DecodeStatus decodeUImmOperandGE(MCInst &Inst, uint32_t Imm,
+                                        int64_t Address,
+                                        const MCDisassembler *Decoder) {
+  assert(isUInt<Width>(Imm) && "Invalid immediate");
+
+  if (Imm < LowerBound)
+    return MCDisassembler::Fail;
+
+  Inst.addOperand(MCOperand::createImm(Imm));
+  return MCDisassembler::Success;
+}
+
 static DecodeStatus decodeUImmLog2XLenOperand(MCInst &Inst, uint32_t Imm,
                                               int64_t Address,
                                               const MCDisassembler *Decoder) {