[RISCV] Update DecoderMethod and MCOperandPredicate of spimm.

[yetingk]

The spimm operand is an immediate that only its 4-5th bits could be setted.

[llvmbot]

@llvm/pr-subscribers-backend-risc-v

Author: Yeting Kuo (yetingk)

Changes

The spimm operand is an immediate whose only 4-5th bits could be setted.

---

Full diff: https://github.com/llvm/llvm-project/pull/76061.diff

2 Files Affected:

• (modified) llvm/lib/Target/RISCV/Disassembler/RISCVDisassembler.cpp (+2-2)
• (modified) llvm/lib/Target/RISCV/RISCVInstrInfoZc.td (+1-1)

diff --git a/llvm/lib/Target/RISCV/Disassembler/RISCVDisassembler.cpp b/llvm/lib/Target/RISCV/Disassembler/RISCVDisassembler.cpp
index 53e2b6b4d94ea0..5c4dbb2249a116 100644
--- a/llvm/lib/Target/RISCV/Disassembler/RISCVDisassembler.cpp
+++ b/llvm/lib/Target/RISCV/Disassembler/RISCVDisassembler.cpp
@@ -462,10 +462,10 @@ static DecodeStatus decodeRegReg(MCInst &Inst, uint32_t Insn, uint64_t Address,
   return MCDisassembler::Success;
 }
 
-// spimm is based on rlist now.
 static DecodeStatus decodeZcmpSpimm(MCInst &Inst, unsigned Imm,
                                     uint64_t Address, const void *Decoder) {
-  // TODO: check if spimm matches rlist
+  if (!isShiftedUInt<2, 4>(Imm))
+    return MCDisassembler::Fail;
   Inst.addOperand(MCOperand::createImm(Imm));
   return MCDisassembler::Success;
 }
diff --git a/llvm/lib/Target/RISCV/RISCVInstrInfoZc.td b/llvm/lib/Target/RISCV/RISCVInstrInfoZc.td
index a78f3624446871..2b3f08bc4a1a4f 100644
--- a/llvm/lib/Target/RISCV/RISCVInstrInfoZc.td
+++ b/llvm/lib/Target/RISCV/RISCVInstrInfoZc.td
@@ -70,7 +70,7 @@ def spimm : Operand<OtherVT> {
     int64_t Imm;
     if (!MCOp.evaluateAsConstantImm(Imm))
       return false;
-    return isShiftedUInt<5, 4>(Imm);
+    return isShiftedUInt<2, 4>(Imm);
   }];
 }
 

[yetingk]

Ping.

[topperc]

Is this testable?

[topperc]

I don't this check can ever fail. The caller looks like

    tmp = fieldFromInstruction(insn, 2, 2) << 4;                                 
    if (!Check(S, decodeZcmpSpimm(MI, tmp, Address, Decoder))) { return MCDisassembler::Fail; }

So its guaranteed to be a isShiftedUInt<2, 4>

[yetingk]

Removed this check. Sorry I didn't survey enough code about this.

[topperc]

LGTM