[mipatternmatch] Document the mi_match() parameters

llvm/include/llvm/CodeGen/GlobalISel/MIPatternMatch.h

 
 #include "llvm/CodeGen/GlobalISel/Utils.h"
 #include "llvm/CodeGen/MachineRegisterInfo.h"
 #include "llvm/IR/InstrTypes.h"
 
 namespace llvm {
 namespace MIPatternMatch {
 
+/// Match a structured pattern of MachineInstrs
+///
+/// \param R The vreg to start matching from. The pattern will begin matching
+///          the instruction that defined this vreg.
+/// \param MRI The MachineRegisterInfo object for the current target
+/// \param Pattern The pattern to match consisting of m_ICst(), m_OneUse(), and
+///                similar nodes. Note: The generated documentation is linking
+///                to an unrelated class with a coinciding name.
 template <typename Reg, typename Pattern>
 bool mi_match(Reg R, const MachineRegisterInfo &MRI, Pattern &&P) {
   return P.match(MRI, R);
 }
 
+/// Match a structured pattern of MachineInstrs
+///
+/// \param MI The MachineInstr to start matching from. It's assumed that
+///           matching is intended to start from one of the vregs it defines.
+/// \param MRI The MachineRegisterInfo object for the current target
+/// \param Pattern The pattern to match consisting of m_ICst(), m_OneUse(), and
+///                similar nodes. Note: The generated documentation is linking
+///                to an unrelated class with a coinciding name.
 template <typename Pattern>
 bool mi_match(MachineInstr &MI, const MachineRegisterInfo &MRI, Pattern &&P) {
   return P.match(MRI, &MI);
 }
 
 // TODO: Extend for N use.
 template <typename SubPatternT> struct OneUse_match {
   SubPatternT SubPat;