[RISCV][MC] Fix >32bit .insn Directives (llvm#111878)

The original patch had a reasonably significant bug. You could not use
`.insn` to assemble encodings that had any bits set above the low 32
bits. This is due to the fact that `getMachineOpValue` was truncating
the immediate value, and I did not commit enough tests of useful cases.

This changes the result of `getMachineOpValue` to be able to return the
48-bit and 64-bit immediates needed for the wider `.insn` directives.

I took the opportunity to move some of the test cases around in the file
to make looking at the output of `llvm-objdump` a little clearer.

llvm/lib/Target/RISCV/MCTargetDesc/RISCVMCCodeEmitter.cpp

@@ -77,7 +77,7 @@ class RISCVMCCodeEmitter : public MCCodeEmitter {
 
   /// Return binary encoding of operand. If the machine operand requires
   /// relocation, record the relocation and return zero.
-  unsigned getMachineOpValue(const MCInst &MI, const MCOperand &MO,
+  uint64_t getMachineOpValue(const MCInst &MI, const MCOperand &MO,
                              SmallVectorImpl<MCFixup> &Fixups,
                              const MCSubtargetInfo &STI) const;
 
@@ -375,7 +375,7 @@ void RISCVMCCodeEmitter::encodeInstruction(const MCInst &MI,
   ++MCNumEmitted; // Keep track of the # of mi's emitted.
 }
 
-unsigned
+uint64_t
 RISCVMCCodeEmitter::getMachineOpValue(const MCInst &MI, const MCOperand &MO,
                                       SmallVectorImpl<MCFixup> &Fixups,
                                       const MCSubtargetInfo &STI) const {
@@ -384,7 +384,7 @@ RISCVMCCodeEmitter::getMachineOpValue(const MCInst &MI, const MCOperand &MO,
     return Ctx.getRegisterInfo()->getEncodingValue(MO.getReg());
 
   if (MO.isImm())
-    return static_cast<unsigned>(MO.getImm());
+    return MO.getImm();
 
   llvm_unreachable("Unhandled expression!");
   return 0;

llvm/test/MC/RISCV/insn.s

@@ -170,17 +170,40 @@ target:
 # CHECK-OBJ: <unknown>
 .insn 6, 0x1f
 
-# CHECK-ASM: .insn 0x4, 65503
-# CHECK-ASM: encoding: [0xdf,0xff,0x00,0x00]
-# CHECK-OBJ: <unknown>
-.insn 0xffdf
-
 # CHECK-ASM: .insn 0x8, 63
 # CHECK-ASM: encoding: [0x3f,0x00,0x00,0x00,0x00,0x00,0x00,0x00]
 # CHECK-OBJ: <unknown>
 .insn 8, 0x3f
 
+# CHECK-ASM: .insn 0x6, 281474976710623
+# CHECK-ASM: encoding: [0xdf,0xff,0xff,0xff,0xff,0xff]
+# CHECK-OBJ: <unknown>
+.insn 0x6, 0xffffffffffdf
+
+# CHECK-ASM: .insn 0x8, -65
+# CHECK-ASM: encoding: [0xbf,0xff,0xff,0xff,0xff,0xff,0xff,0xff]
+# CHECK-OBJ: <unknown>
+.insn 0x8, 0xffffffffffffffbf
+
+odd_lengths:
+# CHECK-ASM-LABEL: odd_lengths:
+# CHECK-OBJ-LABEL: <odd_lengths>:
+
+## These deliberately disagree with the lengths objdump expects them to have, so
+## keep them at the end so that the disassembled instruction stream is not out
+## of sync with the encoded instruction stream. We don't check for `<unknown>`
+## as we could get any number of those, so instead check for the encoding
+## halfwords. These might be split into odd 16-bit chunks, so each chunk is on
+## one line.
+
+# CHECK-ASM: .insn 0x4, 65503
+# CHECK-ASM: encoding: [0xdf,0xff,0x00,0x00]
+# CHECK-OBJ: ffdf
+# CHECK-OBJ: 0000
+.insn 0xffdf
+
 # CHECK-ASM: .insn 0x4, 65471
 # CHECK-ASM: encoding: [0xbf,0xff,0x00,0x00]
-# CHECK-OBJ: <unknown>
+# CHECK-OBJ: ffbf
+# CHECK-OBJ: 0000
 .insn 0xffbf