[AsmPrinter] Remove const qualifier from EmitBasicBlockStart.

[ebevhan]

Summary

Overriders may want to modify state in it. AMDGPU wants
to, but has to make its members mutable in order to do so.

Besides, EmitBasicBlockEnd is not const, so why should
Start be?

[nickdesaulniers]

Bonus points for *removing* the use of mutable.

include/llvm/CodeGen/AsmPrinter.h

public:
   /// Targets can override this to emit stuff after the last basic block in the
   /// function.
   virtual void EmitFunctionBodyEnd() {}
 
   /// Targets can override this to emit stuff at the start of a basic block.
   /// By default, this method prints the label for the specified
   /// MachineBasicBlock, an alignment (if present) and a comment describing it
   /// if appropriate.
-  virtual void EmitBasicBlockStart(const MachineBasicBlock &MBB) const;
+  virtual void EmitBasicBlockStart(const MachineBasicBlock &MBB);
 
   /// Targets can override this to emit stuff at the end of a basic block.
   virtual void EmitBasicBlockEnd(const MachineBasicBlock &MBB);
 
   /// Targets should implement this to emit instructions.
   virtual void EmitInstruction(const MachineInstr *) {
     llvm_unreachable("EmitInstruction not implemented");
   }

lib/CodeGen/AsmPrinter/AsmPrinter.cpp

Context.IsBasicBlockReachableViaFallthrough =
       MBB.pred_end();
   Context.IsBasicBlockReachableViaBranch =
       MBB.pred_size() > 0 && !isBlockOnlyReachableByFallthrough(&MBB);
 }
 
 /// EmitBasicBlockStart - This method prints the label for the specified
 /// MachineBasicBlock, an alignment (if present) and a comment describing
 /// it if appropriate.
-void AsmPrinter::EmitBasicBlockStart(const MachineBasicBlock &MBB) const {
+void AsmPrinter::EmitBasicBlockStart(const MachineBasicBlock &MBB) {
   // End the previous funclet and start a new one.
   if (MBB.isEHFuncletEntry()) {
     for (const HandlerInfo &HI : Handlers) {
       HI.Handler->endFunclet();
       HI.Handler->beginFunclet(MBB);
     }
   }
 

lib/Target/AMDGPU/AMDGPUAsmPrinter.h

public:
   void EmitInstruction(const MachineInstr *MI) override;
 
   void EmitFunctionBodyStart() override;
 
   void EmitFunctionBodyEnd() override;
 
   void EmitFunctionEntryLabel() override;
 
-  void EmitBasicBlockStart(const MachineBasicBlock &MBB) const override;
+  void EmitBasicBlockStart(const MachineBasicBlock &MBB) override;
 
   void EmitGlobalVariable(const GlobalVariable *GV) override;
 
   void EmitStartOfAsmFile(Module &M) override;
 
   void EmitEndOfAsmFile(Module &M) override;
 
   bool isBlockOnlyReachableByFallthrough(
     const MachineBasicBlock *MBB) const override;
 
   bool PrintAsmOperand(const MachineInstr *MI, unsigned OpNo,
                        const char *ExtraCode, raw_ostream &O) override;
 
 protected:
-  mutable std::vector<std::string> DisasmLines, HexLines;
-  mutable size_t DisasmLineMaxLen;
+  std::vector<std::string> DisasmLines, HexLines;
+  size_t DisasmLineMaxLen;
 };
 
 } // end namespace llvm
 
 #endif // LLVM_LIB_TARGET_AMDGPU_AMDGPUASMPRINTER_H

lib/Target/AMDGPU/AMDGPUAsmPrinter.cpp

if (DumpCodeInstEmitter) {
     DisasmLines.push_back(MF->getName().str() + ":");
     DisasmLineMaxLen = std::max(DisasmLineMaxLen, DisasmLines.back().size());
     HexLines.push_back("");
   }
 
   AsmPrinter::EmitFunctionEntryLabel();
 }
 
-void AMDGPUAsmPrinter::EmitBasicBlockStart(const MachineBasicBlock &MBB) const {
+void AMDGPUAsmPrinter::EmitBasicBlockStart(const MachineBasicBlock &MBB) {
   if (DumpCodeInstEmitter && !isBlockOnlyReachableByFallthrough(&MBB)) {
     // Write a line for the basic block label if it is not only fallthrough.
     DisasmLines.push_back(
         (Twine("BB") + Twine(getFunctionNumber())
          + "_" + Twine(MBB.getNumber()) + ":").str());
     DisasmLineMaxLen = std::max(DisasmLineMaxLen, DisasmLines.back().size());
     HexLines.push_back("");
   }

lib/Target/NVPTX/NVPTXAsmPrinter.h

class LLVM_LIBRARY_VISIBILITY NVPTXAsmPrinter : public AsmPrinter {
   friend class AggBuffer;
 
 private:
   StringRef getPassName() const override { return "NVPTX Assembly Printer"; }
 
   const Function *F;
   std::string CurrentFnName;
 
-  void EmitBasicBlockStart(const MachineBasicBlock &MBB) const override;
+  void EmitBasicBlockStart(const MachineBasicBlock &MBB) override;
   void EmitFunctionEntryLabel() override;
   void EmitFunctionBodyStart() override;
   void EmitFunctionBodyEnd() override;
   void emitImplicitDef(const MachineInstr *MI) const override;
 
   void EmitInstruction(const MachineInstr *) override;
   void lowerToMCInst(const MachineInstr *MI, MCInst &OutMI);
   bool lowerOperand(const MachineOperand &MO, MCOperand &MCOp);

lib/Target/NVPTX/NVPTXAsmPrinter.cpp

if (const BasicBlock *PBB = PMBB->getBasicBlock()) {
         if (GetUnrollMetadata(LoopID, "llvm.loop.unroll.disable"))
           return true;
       }
     }
   }
   return false;
 }
 
-void NVPTXAsmPrinter::EmitBasicBlockStart(const MachineBasicBlock &MBB) const {
+void NVPTXAsmPrinter::EmitBasicBlockStart(const MachineBasicBlock &MBB) {
   AsmPrinter::EmitBasicBlockStart(MBB);
   if (isLoopHeaderOfNoUnroll(MBB))
     OutStreamer->EmitRawText(StringRef("\t.pragma \"nounroll\";\n"));
 }
 
 void NVPTXAsmPrinter::EmitFunctionEntryLabel() {
   SmallString<128> Str;
   raw_svector_ostream O(Str);