[DebugInfo] Tidy up DbgValueLocation class

[Orlando]

Summary

Mostly NFC. These changes are in preparation for the work done in D74053.

Commit ed29dbaafa49 removed the WasIndirect field from DbgValueLocation so
I've removed some checks that were hanging around and tidied up the class:

• Fix locNo() method: it no longer needs to work around the WasIndirect bitfield.

• Remove assertions from constructor: it no longer needs to check the bitfield packing.

• Use defaulted default constructor and in-class member initializer values.

[aprantl]

llvm/lib/CodeGen/LiveDebugVariables.cpp

105

getLocNo()?

108

Without having read the context, this function seems pointless and redundant with the constructor?

123

why u?

[Orlando]

llvm/lib/CodeGen/LiveDebugVariables.cpp

105

I have done this in D74055, another NFC which is dependant on the functional change, to keep this diff smaller because it touches each of the locNo() call sites to update the variable names.

108

This becomes useful in the next patch D74053 (the functional change).

123

No particular reason, I am happy to remove it.

[Orlando]

Thanks for reviewing this. Unfortunately the changes made in ed29dbaafa49 (D68945) were just reverted in 6531a78ac4b5 so this patch is no longer necessary.

llvm/lib/CodeGen/LiveDebugVariables.cpp

 }
 
 LiveDebugVariables::LiveDebugVariables() : MachineFunctionPass(ID) {
   initializeLiveDebugVariablesPass(*PassRegistry::getPassRegistry());
 }
 
 enum : unsigned { UndefLocNo = ~0U };
 
-/// Describes a location by number along with some flags about the original
-/// usage of the location.
+/// Describes a debug variable location by number.
 class DbgValueLocation {
 public:
-  DbgValueLocation(unsigned LocNo)
-      : LocNo(LocNo) {
-    static_assert(sizeof(*this) == sizeof(unsigned), "bad bitfield packing");
-    assert(locNo() == LocNo && "location truncation");
-  }
-
-  DbgValueLocation() : LocNo(0) {}
+  DbgValueLocation() = default;
+  DbgValueLocation(unsigned LocNo) : LocNo(LocNo) {}
 
-  unsigned locNo() const {
-    // Fix up the undef location number, which gets truncated.
-    return LocNo == INT_MAX ? UndefLocNo : LocNo;
-  }
+  unsigned locNo() const { return LocNo; }
   bool isUndef() const { return locNo() == UndefLocNo; }
 
   DbgValueLocation changeLocNo(unsigned NewLocNo) const {
     return DbgValueLocation(NewLocNo);
   }
 
   friend inline bool operator==(const DbgValueLocation &LHS,
                                 const DbgValueLocation &RHS) {
     return LHS.LocNo == RHS.LocNo;
   }
 
   friend inline bool operator!=(const DbgValueLocation &LHS,
                                 const DbgValueLocation &RHS) {
     return !(LHS == RHS);
   }
 
 private:
-  unsigned LocNo;
+  unsigned LocNo = 0u;
 };
 
 /// Map of where a user value is live, and its location.
 using LocMap = IntervalMap<SlotIndex, DbgValueLocation, 4>;
 
 /// Map of stack slot offsets for spilled locations.
 /// Non-spilled locations are not added to the map.
 using SpillOffsetMap = DenseMap<unsigned, unsigned>;