[NFC][AsmPrinter] Make comments for spill/reload more precise.

[HsiangKai]

Summary

The size of spill/reload may be unknown for scalable vector types. When the size is unknown, print it as "Unknown size" instead of a very large number.

[evandro]

If you happen to have a test case, please, consider adding it.

[frasercrmck]

LGTM. The only thing I'd say is that "Unknown size" isn't an adjective like "4-byte" is. I'm not sure if "Unknown-sized" is any better, though.

llvm/lib/CodeGen/AsmPrinter/AsmPrinter.cpp

 #include "llvm/ADT/SmallString.h"
 #include "llvm/ADT/SmallVector.h"
 #include "llvm/ADT/Statistic.h"
 #include "llvm/ADT/StringRef.h"
 #include "llvm/ADT/Triple.h"
 #include "llvm/ADT/Twine.h"
 #include "llvm/Analysis/ConstantFolding.h"
 #include "llvm/Analysis/EHPersonalities.h"
+#include "llvm/Analysis/MemoryLocation.h"
 #include "llvm/Analysis/OptimizationRemarkEmitter.h"
 #include "llvm/BinaryFormat/COFF.h"
 #include "llvm/BinaryFormat/Dwarf.h"
 #include "llvm/BinaryFormat/ELF.h"
 #include "llvm/CodeGen/GCMetadata.h"
 #include "llvm/CodeGen/GCMetadataPrinter.h"
 #include "llvm/CodeGen/GCStrategy.h"
 #include "llvm/CodeGen/MachineBasicBlock.h"
static void emitComments(const MachineInstr &MI, raw_ostream &CommentOS) {
   // Check for spills and reloads
 
   // We assume a single instruction only has a spill or reload, not
   // both.
   Optional<unsigned> Size;
   if ((Size = MI.getRestoreSize(TII))) {
     CommentOS << *Size << "-byte Reload\n";
   } else if ((Size = MI.getFoldedRestoreSize(TII))) {
-    if (*Size)
+    if (*Size) {
+      if (*Size == static_cast<unsigned>(MemoryLocation::UnknownSize))
+        CommentOS << "Unknown-size Folded Reload\n";
+      else
         CommentOS << *Size << "-byte Folded Reload\n";
+    }
   } else if ((Size = MI.getSpillSize(TII))) {
     CommentOS << *Size << "-byte Spill\n";
   } else if ((Size = MI.getFoldedSpillSize(TII))) {
-    if (*Size)
+    if (*Size) {
+      if (*Size == static_cast<unsigned>(MemoryLocation::UnknownSize))
+        CommentOS << "Unknown-size Folded Spill\n";
+      else
         CommentOS << *Size << "-byte Folded Spill\n";
     }
+  }
 
   // Check for spill-induced copies
   if (MI.getAsmPrinterFlag(MachineInstr::ReloadReuse))
     CommentOS << " Reload Reuse\n";
 }
 
 /// emitImplicitDef - This method emits the specified machine instruction
 /// that is an implicit def.