[llvm-exegesis] Don't use unsupported aliasing instructions

[mstojanovic]

Summary

Since some instruction types aren't allowed as the main instruction also don't allow them for aliasing instructions.

[courbet]

Great, I did that for target-specific instructions yesterday (D73161), this is the target-agnostic part. Thanks.

llvm/tools/llvm-exegesis/lib/SerialSnippetGenerator.cpp

computeAliasingInstructions(const LLVMState &State, const Instruction *Instr,
   std::iota(Opcodes.begin(), Opcodes.end(), 0U);
   std::shuffle(Opcodes.begin(), Opcodes.end(), randomGenerator());
 
   std::vector<const Instruction *> AliasingInstructions;
   for (const unsigned OtherOpcode : Opcodes) {
     if (OtherOpcode == Instr->Description.getOpcode())
       continue;
     const Instruction &OtherInstr = State.getIC().getInstr(OtherOpcode);
+    const MCInstrDesc &OtherInstrDesc = OtherInstr.Description;
+    // Ignore instructions that we cannot run.
+    if (OtherInstrDesc.isPseudo() ||
+        OtherInstrDesc.isBranch() || OtherInstrDesc.isIndirectBranch() ||
+        OtherInstrDesc.isCall() || OtherInstrDesc.isReturn()) {
+          continue;
+    }
     if (OtherInstr.hasMemoryOperands())
       continue;
     if (!State.getExegesisTarget().allowAsBackToBack(OtherInstr))
       continue;
     if (Instr->hasAliasingRegistersThrough(OtherInstr, ForbiddenRegisters))
       AliasingInstructions.push_back(&OtherInstr);
     if (AliasingInstructions.size() >= MaxAliasingInstructions)
       break;