[AMDGPU] Use new hasDummyOperands on vop3_real

[tpr]

Summary

This ensures that the MC decoder leaves a dummy operand for the missing
src2 modifiers on a mac, without the hack to insert it manually.

This change requires D49027.

Change-Id: I18681ee99da9c5b9650ee05d5d305a8e5d0dfe09

lib/Target/AMDGPU/Disassembler/AMDGPUDisassembler.cpp

do {
     if (Res) break;
 
     Res = tryDecodeInst(DecoderTableAMDGPU64, MI, QW, Address);
     if (Res) break;
 
     Res = tryDecodeInst(DecoderTableGFX964, MI, QW, Address);
   } while (false);
 
-  if (Res && (MI.getOpcode() == AMDGPU::V_MAC_F32_e64_vi ||
-              MI.getOpcode() == AMDGPU::V_MAC_F32_e64_si ||
-              MI.getOpcode() == AMDGPU::V_MAC_F16_e64_vi ||
-              MI.getOpcode() == AMDGPU::V_FMAC_F32_e64_vi)) {
-    // Insert dummy unused src2_modifiers.
-    insertNamedMCOperand(MI, MCOperand::createImm(0),
-                         AMDGPU::OpName::src2_modifiers);
-  }
-
   if (Res && (MCII->get(MI.getOpcode()).TSFlags & SIInstrFlags::MIMG)) {
     Res = convertMIMGInst(MI);
   }
 
   if (Res && IsSDWA)
     Res = convertSDWAInst(MI);
 
   // if the opcode was not recognized we'll assume a Size of 4 bytes

lib/Target/AMDGPU/VOPInstructions.td

 
 class VOP3_Real <VOP_Pseudo ps, int EncodingFamily> :
   InstSI <ps.OutOperandList, ps.InOperandList, ps.Mnemonic # ps.AsmOperands, []>,
   SIMCInstr <ps.PseudoInstr, EncodingFamily> {
 
   let isPseudo = 0;
   let isCodeGenOnly = 0;
   let UseNamedOperandTable = 1;
+  // Leave a gap when decoding a vop3 mac for the missing src2 modifiers.
+  let hasDummyOperands = 1;
 
   let Constraints     = ps.Constraints;
   let DisableEncoding = ps.DisableEncoding;
 
   // copy relevant pseudo op flags
   let SubtargetPredicate = ps.SubtargetPredicate;
   let AsmMatchConverter  = ps.AsmMatchConverter;
   let AsmVariantName     = ps.AsmVariantName;