[RegAlloc] Simplify RegAllocEvictionAdvisor::canReassign (NFC)

[barannikov88]

Summary

Use range-based for loops.
The return type has been changed to bool because the method is only
used in boolean contexts.

llvm/lib/CodeGen/RegAllocEvictionAdvisor.h

public:
 
   /// Returns true if the given \p PhysReg is a callee saved register and has
   /// not been used for allocation yet.
   bool isUnusedCalleeSavedReg(MCRegister PhysReg) const;
 
 protected:
   RegAllocEvictionAdvisor(const MachineFunction &MF, const RAGreedy &RA);
 
-  Register canReassign(const LiveInterval &VirtReg, Register PrevReg) const;
+  bool canReassign(const LiveInterval &VirtReg, MCRegister FromReg) const;
 
   // Get the upper limit of elements in the given Order we need to analize.
   // TODO: is this heuristic,  we could consider learning it.
   std::optional<unsigned> getOrderLimit(const LiveInterval &VirtReg,
                                         const AllocationOrder &Order,
                                         unsigned CostPerUseLimit) const;
 
   // Determine if it's worth trying to allocate this reg, given the

llvm/lib/CodeGen/RegAllocGreedy.cpp

MCRegister RAGreedy::tryAssign(const LiveInterval &VirtReg,
   MCRegister CheapReg = tryEvict(VirtReg, Order, NewVRegs, Cost, FixedRegisters);
   return CheapReg ? CheapReg : PhysReg;
 }
 
 //===----------------------------------------------------------------------===//
 //                         Interference eviction
 //===----------------------------------------------------------------------===//
 
-Register RegAllocEvictionAdvisor::canReassign(const LiveInterval &VirtReg,
-                                              Register PrevReg) const {
-  auto Order =
-      AllocationOrder::create(VirtReg.reg(), *VRM, RegClassInfo, Matrix);
-  MCRegister PhysReg;
-  for (auto I = Order.begin(), E = Order.end(); I != E && !PhysReg; ++I) {
-    if ((*I).id() == PrevReg.id())
-      continue;
-
-    MCRegUnitIterator Units(*I, TRI);
-    for (; Units.isValid(); ++Units) {
-      // Instantiate a "subquery", not to be confused with the Queries array.
-      LiveIntervalUnion::Query subQ(VirtReg, Matrix->getLiveUnions()[*Units]);
-      if (subQ.checkInterference())
-        break;
+bool RegAllocEvictionAdvisor::canReassign(const LiveInterval &VirtReg,
+                                          MCRegister FromReg) const {
+  auto HasRegUnitInterference = [&](MCRegUnit Unit) {
+    LiveIntervalUnion::Query SubQ(VirtReg, Matrix->getLiveUnions()[Unit]);
+    return SubQ.checkInterference();
+  };
+
+  for (MCRegister Reg :
+       AllocationOrder::create(VirtReg.reg(), *VRM, RegClassInfo, Matrix)) {
+    if (Reg == FromReg)
+      continue;
+    // If no units have interference, reassignment is possible.
+    if (none_of(TRI->regunits(Reg), HasRegUnitInterference)) {
+      LLVM_DEBUG(dbgs() << "can reassign: " << VirtReg << " from "
+                        << printReg(FromReg, TRI) << " to "
+                        << printReg(Reg, TRI) << '\n');
+      return true;
     }
-    // If no units have interference, break out with the current PhysReg.
-    if (!Units.isValid())
-      PhysReg = *I;
   }
-  if (PhysReg)
-    LLVM_DEBUG(dbgs() << "can reassign: " << VirtReg << " from "
-                      << printReg(PrevReg, TRI) << " to "
-                      << printReg(PhysReg, TRI) << '\n');
-  return PhysReg;
+  return false;
 }
 
 /// evictInterference - Evict any interferring registers that prevent VirtReg
 /// from being assigned to Physreg. This assumes that canEvictInterference
 /// returned true.
 void RAGreedy::evictInterference(const LiveInterval &VirtReg,
                                  MCRegister PhysReg,
                                  SmallVectorImpl<Register> &NewVRegs) {