[NFC] Remove dead code

[gchatelet]

Summary

@t.p.northover as a code owner for various ARM parts can you have a look at the ByValInfo struct?
Everything still compiles fine without the Waste field, I patched the description but it might be updated with a better wording, WDYT?

[gchatelet]

rebasing

[gchatelet]

rebase

[gchatelet]

@kristof.beyls what do you think about this patch? Does it make sense?

[gchatelet]

I'll go ahead and submit it.

llvm/include/llvm/CodeGen/CallingConvLower.h

private:
   // then, for function "foo":
   //
   // i32 foo(i32 %p, %struct_type* %r, i32 %s, %struct_type* %t)
   //
   // ByValRegs[0] describes how "%r" is stored (Begin == r1, End == r2)
   // ByValRegs[1] describes how "%t" is stored (Begin == r3, End == r4).
   //
   // In case of 8 bytes stack alignment,
-  // ByValRegs may also contain information about wasted registers.
   // In function shown above, r3 would be wasted according to AAPCS rules.
-  // And in that case ByValRegs[1].Waste would be "true".
   // ByValRegs vector size still would be 2,
   // while "%t" goes to the stack: it wouldn't be described in ByValRegs.
   //
   // Supposed use-case for this collection:
   // 1. Initially ByValRegs is empty, InRegsParamsProcessed is 0.
   // 2. HandleByVal fillups ByValRegs.
   // 3. Argument analysis (LowerFormatArguments, for example). After
   // some byval argument was analyzed, InRegsParamsProcessed is increased.
   struct ByValInfo {
-    ByValInfo(unsigned B, unsigned E, bool IsWaste = false) :
-      Begin(B), End(E), Waste(IsWaste) {}
+    ByValInfo(unsigned B, unsigned E) : Begin(B), End(E) {}
+
     // First register allocated for current parameter.
     unsigned Begin;
 
     // First after last register allocated for current parameter.
     unsigned End;
-
-    // Means that current range of registers doesn't belong to any
-    // parameters. It was wasted due to stack alignment rules.
-    // For more information see:
-    // AAPCS, 5.5 Parameter Passing, Stage C, C.3.
-    bool Waste;
   };
   SmallVector<ByValInfo, 4 > ByValRegs;
 
   // InRegsParamsProcessed - shows how many instances of ByValRegs was proceed
   // during argument analysis.
   unsigned InRegsParamsProcessed;
 
 public: