[RISCV] Enable MCCodeEmitter instruction predicate verifier

This ensures that we never encode an instruction which is unavailable,
such as if we explicitly insert a forbidden instruction when lowering.
This is particularly important on RISC-V given its high degree of
modularity, and will become increasingly important as new standard
extensions appear.

Reviewed By: asb, lenary

Differential Revision: https://reviews.llvm.org/D85015

Author: jrtc27

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

@@ -84,6 +84,12 @@ class RISCVMCCodeEmitter : public MCCodeEmitter {
   unsigned getVMaskReg(const MCInst &MI, unsigned OpNo,
                        SmallVectorImpl<MCFixup> &Fixups,
                        const MCSubtargetInfo &STI) const;
+
+private:
+  FeatureBitset computeAvailableFeatures(const FeatureBitset &FB) const;
+  void
+  verifyInstructionPredicates(const MCInst &MI,
+                              const FeatureBitset &AvailableFeatures) const;
 };
 } // end anonymous namespace
 
@@ -185,6 +191,9 @@ void RISCVMCCodeEmitter::expandAddTPRel(const MCInst &MI, raw_ostream &OS,
 void RISCVMCCodeEmitter::encodeInstruction(const MCInst &MI, raw_ostream &OS,
                                            SmallVectorImpl<MCFixup> &Fixups,
                                            const MCSubtargetInfo &STI) const {
+  verifyInstructionPredicates(MI,
+                              computeAvailableFeatures(STI.getFeatureBits()));
+
   const MCInstrDesc &Desc = MCII.get(MI.getOpcode());
   // Get byte count of instruction.
   unsigned Size = Desc.getSize();
@@ -397,4 +406,5 @@ unsigned RISCVMCCodeEmitter::getVMaskReg(const MCInst &MI, unsigned OpNo,
   }
 }
 
+#define ENABLE_INSTR_PREDICATE_VERIFIER
 #include "RISCVGenMCCodeEmitter.inc"