[GISel]: More flexibility while building I/FCmps with MachineIRBuilder

[dsanders]

Hi Aditya,

The subject and summary needs to better explain what the change is doing. There should also be something that uses the new functions otherwise they'll be deleted as dead code at some point in the future.

[aditya_nandakumar]

Hi Daniel - having these methods would let me use them in https://reviews.llvm.org/D35737. Right now they are not related.

[dsanders]

Hi Aditya,

Do you still need these?

[aditya_nandakumar]

Yes. These would still be useful.

include/llvm/CodeGen/GlobalISel/MachineIRBuilder.h

public:
   /// \pre \p Op0 and Op1 must be generic virtual registers with the
   ///      same number of elements as \p Res. If \p Res is a scalar,
   ///      \p Op0 must be either a scalar or pointer.
   /// \pre \p Pred must be an integer predicate.
   ///
   /// \return a MachineInstrBuilder for the newly created instruction.
   MachineInstrBuilder buildICmp(CmpInst::Predicate Pred,
                                 unsigned Res, unsigned Op0, unsigned Op1);
+  template <typename DstTy, typename... UseArgsTy>
+  MachineInstrBuilder buildICmp(CmpInst::Predicate Pred, DstTy &&Ty,
+                                UseArgsTy &&... UseArgs) {
+    return buildICmp(Pred, getDestFromArg(Ty), (getRegFromArg(UseArgs))...);
+  }
 
   /// Build and insert a \p Res = G_FCMP \p Pred\p Op0, \p Op1
   ///
   /// \pre setBasicBlock or setMI must have been called.
 
   /// \pre \p Res must be a generic virtual register with scalar or
   ///      vector type. Typically this starts as s1 or <N x s1>.
   /// \pre \p Op0 and Op1 must be generic virtual registers with the
   ///      same number of elements as \p Res (or scalar, if \p Res is
   ///      scalar).
   /// \pre \p Pred must be a floating-point predicate.
   ///
   /// \return a MachineInstrBuilder for the newly created instruction.
   MachineInstrBuilder buildFCmp(CmpInst::Predicate Pred,
                                 unsigned Res, unsigned Op0, unsigned Op1);
+  template <typename DstTy, typename... UseArgsTy>
+  MachineInstrBuilder buildFCmp(CmpInst::Predicate Pred, DstTy &&Ty,
+                                UseArgsTy &&... UseArgs) {
+    return buildFCmp(Pred, getDestFromArg(Ty), (getRegFromArg(UseArgs))...);
+  }
 
   /// Build and insert a \p Res = G_SELECT \p Tst, \p Op0, \p Op1
   ///
   /// \pre setBasicBlock or setMI must have been called.
   /// \pre \p Res, \p Op0 and \p Op1 must be generic virtual registers
   ///      with the same type.
   /// \pre \p Tst must be a generic virtual register with scalar, pointer or
   ///      vector type. If vector then it must have the same number of