ARC: Enforce function alignment at code emission time

[arsenm]

Summary

Don't do this in the MachineFunctionInfo constructor. Also, ensure the
alignment rather than overwriting it outright. I vaguely remember
there was another place to enforce the target minimum alignment, but I
couldn't find it (it's there for instructions).

[petecoup]

Were we the only target doing this? Regardless, this seems fine to me, thanks!

[arsenm]

In D82094#2101285, @petecoup wrote:

Were we the only target doing this? Regardless, this seems fine to me, thanks!

Nothing else was modifying the function here. Some others are still doing something with the machine function which I intend to fix

[arsenm]

bbd78519f9a15669580563b93a3ab5d4cad1febc

llvm/lib/Target/ARC/ARCAsmPrinter.cpp

 public:
   explicit ARCAsmPrinter(TargetMachine &TM,
                          std::unique_ptr<MCStreamer> Streamer)
       : AsmPrinter(TM, std::move(Streamer)),
         MCInstLowering(&OutContext, *this) {}
 
   StringRef getPassName() const override { return "ARC Assembly Printer"; }
   void emitInstruction(const MachineInstr *MI) override;
+
+  bool runOnMachineFunction(MachineFunction &MF) override;
 };
 
 } // end anonymous namespace
 
 void ARCAsmPrinter::emitInstruction(const MachineInstr *MI) {
   SmallString<128> Str;
   raw_svector_ostream O(Str);
 
   switch (MI->getOpcode()) {
   case ARC::DBG_VALUE:
     llvm_unreachable("Should be handled target independently");
     break;
   }
 
   MCInst TmpInst;
   MCInstLowering.Lower(MI, TmpInst);
   EmitToStreamer(*OutStreamer, TmpInst);
 }
 
+bool ARCAsmPrinter::runOnMachineFunction(MachineFunction &MF) {
+  // Functions are 4-byte aligned.
+  MF.ensureAlignment(Align(4));
+  AsmPrinter::runOnMachineFunction(MF);
+}
+
 // Force static initialization.
 extern "C" LLVM_EXTERNAL_VISIBILITY void LLVMInitializeARCAsmPrinter() {
   RegisterAsmPrinter<ARCAsmPrinter> X(getTheARCTarget());
 }