[llvm] [RISCV] Fix the disassembler's handling of C.LUI when imm=0 (PR #133450)

[Craig Topper via llvm-commits]

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@@ -453,9 +453,10 @@ static DecodeStatus decodeCLUIImmOperand(MCInst &Inst, uint32_t Imm,
                                          int64_t Address,
                                          const MCDisassembler *Decoder) {
   assert(isUInt<6>(Imm) && "Invalid immediate");
-  if (Imm > 31) {
+  if (Imm == 0)
+    return MCDisassembler::Fail;
+  if (Imm > 31)
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topperc wrote:

This `Imm > 31` check seems unnecessary. SignExtend64<6> won't do anything to a number less than or equal to 31. But we don't have to change it in this patch.

https://github.com/llvm/llvm-project/pull/133450