[llvm-exegesis] Add HasNoSchedulingInfo flag to MCInstDesc.

This allows llvm-exegesis to skip instructions that lack scheduling
information, avoiding invalid benchmarking. e.g. `InstB` in RISC-V.

Author: tclin914

llvm/include/llvm/MC/MCInstrDesc.h

@@ -188,6 +188,7 @@ enum Flag {
   Trap,
   VariadicOpsAreDefs,
   Authenticated,
+  HasNoSchedulingInfo,
 };
 } // namespace MCID
 
@@ -430,6 +431,11 @@ class MCInstrDesc {
     return Flags & (1ULL << MCID::Authenticated);
   }
 
+  /// Return true if this instruction has no scheduling info.
+  bool hasNoSchedulingInfo() const {
+    return Flags & (1ULL << MCID::HasNoSchedulingInfo);
+  }
+
   //===--------------------------------------------------------------------===//
   // Side Effect Analysis
   //===--------------------------------------------------------------------===//

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

@@ -45,6 +45,8 @@ ExegesisTarget::getIgnoredOpcodeReasonOrNull(const LLVMState &State,
     return "Unsupported opcode: isBranch/isIndirectBranch";
   if (InstrDesc.isCall() || InstrDesc.isReturn())
     return "Unsupported opcode: isCall/isReturn";
+  if (InstrDesc.hasNoSchedulingInfo())
+    return "Unsupported opcode: hasNoSchedulingInfo";
   return nullptr;
 }
 

llvm/utils/TableGen/InstrInfoEmitter.cpp

@@ -1199,6 +1199,8 @@ void InstrInfoEmitter::emitRecord(
     OS << "|(1ULL<<MCID::VariadicOpsAreDefs)";
   if (Inst.isAuthenticated)
     OS << "|(1ULL<<MCID::Authenticated)";
+  if (Inst.hasNoSchedulingInfo)
+    OS << "|(1ULL<<MCID::HasNoSchedulingInfo)";
 
   // Emit all of the target-specific flags...
   const BitsInit *TSF = Inst.TheDef->getValueAsBitsInit("TSFlags");