[llvm][Support] Add isZero method for TypeSize. [NFC]

[fpetrogalli]

Summary

The method is used where TypeSize is implicitly cast to integer for
being checked against 0.

[fpetrogalli]

I removed an instance of the isNonZero method, as the patch relates
only to the isZero method. I'll create a separate patch for that.

[sdesmalen]

LGTM, thanks!

While this patch is quite trivial, for other patches, you may want to add a few more reviewers.

[sdesmalen]

llvm/include/llvm/Support/TypeSize.h

153

nit: I mentioned this to Graham when he first proposed TypeSize, but having this variable named 'MinSize' is a bit odd when you compare with Zero, because in a sense, the minimum size of <anything> is always zero :)

[fpetrogalli]

In D76748#1944851, @sdesmalen wrote:

LGTM, thanks!

While this patch is quite trivial, for other patches, you may want to add a few more reviewers.

Sure, will do. Added @efriedma for visibility, I'll wait some time before submitting to give them the possibility to comment in case they want to.

Thanks,

Francesco

llvm/include/llvm/Support/TypeSize.h

153

Agree. Shall we rename it to KnownSize, and consequently rename the get method to getKnownSize?

Thanks for the review!

[fpetrogalli]

llvm/include/llvm/Support/TypeSize.h

153

Of course, in a separate patch! :)

[efriedma]

LGTM

llvm/include/llvm/Support/TypeSize.h

public:
   // Returns true if the number of bits is a multiple of an 8-bit byte.
   bool isByteSized() const {
     return (MinSize & 7) == 0;
   }
 
   // Returns true if the type size is non-zero.
   bool isNonZero() const { return MinSize != 0; }
 
+  // Returns true if the type size is zero.
+  bool isZero() const { return MinSize == 0; }
+
   // Casts to a uint64_t if this is a fixed-width size.
   //
   // This interface is deprecated and will be removed in a future version
   // of LLVM in favour of upgrading uses that rely on this implicit conversion
   // to uint64_t. Calls to functions that return a TypeSize should use the
   // proper interfaces to TypeSize.
   // In practice this is mostly calls to MVT/EVT::getSizeInBits().
   //

llvm/lib/Analysis/ConstantFolding.cpp

do {
     // castable to implement the "load" semantic model.
     if (SrcTy->isStructTy()) {
       // Struct types might have leading zero-length elements like [0 x i32],
       // which are certainly not what we are looking for, so skip them.
       unsigned Elem = 0;
       Constant *ElemC;
       do {
         ElemC = C->getAggregateElement(Elem++);
-      } while (ElemC && DL.getTypeSizeInBits(ElemC->getType()) == 0);
+      } while (ElemC && DL.getTypeSizeInBits(ElemC->getType()).isZero());
       C = ElemC;
     } else {
       C = C->getAggregateElement(0u);
     }
   } while (C);
 
   return nullptr;
 }

llvm/lib/CodeGen/LowLevelType.cpp

LLT llvm::getLLTForType(Type &Ty, const DataLayout &DL) {
   if (auto PTy = dyn_cast<PointerType>(&Ty)) {
     unsigned AddrSpace = PTy->getAddressSpace();
     return LLT::pointer(AddrSpace, DL.getPointerSizeInBits(AddrSpace));
   }
 
   if (Ty.isSized()) {
     // Aggregates are no different from real scalars as far as GlobalISel is
     // concerned.
-    auto SizeInBits = DL.getTypeSizeInBits(&Ty);
-    assert(SizeInBits != 0 && "invalid zero-sized type");
-    return LLT::scalar(SizeInBits);
+    TypeSize SizeInBits = DL.getTypeSizeInBits(&Ty);
+    assert(SizeInBits.isNonZero() && "invalid zero-sized type");
+    assert(!SizeInBits.isScalable() && "Invalid TypeSize.");
+    return LLT::scalar(SizeInBits.getKnownMinSize());
   }
 
   return LLT();
 }
 
 MVT llvm::getMVTForLLT(LLT Ty) {
   if (!Ty.isVector())
     return MVT::getIntegerVT(Ty.getSizeInBits());

llvm/lib/Target/AArch64/AArch64CallLowering.cpp

bool AArch64CallLowering::lowerFormalArguments(
   MachineFunction &MF = MIRBuilder.getMF();
   MachineBasicBlock &MBB = MIRBuilder.getMBB();
   MachineRegisterInfo &MRI = MF.getRegInfo();
   auto &DL = F.getParent()->getDataLayout();
 
   SmallVector<ArgInfo, 8> SplitArgs;
   unsigned i = 0;
   for (auto &Arg : F.args()) {
-    if (DL.getTypeStoreSize(Arg.getType()) == 0)
+    if (DL.getTypeStoreSize(Arg.getType()).isZero())
       continue;
 
     ArgInfo OrigArg{VRegs[i], Arg.getType()};
     setArgFlags(OrigArg, i + AttributeList::FirstArgIndex, DL, F);
 
     splitToValueTypes(OrigArg, SplitArgs, DL, MRI, F.getCallingConv());
     ++i;
   }