Index: lib/Target/SystemZ/SystemZRegisterInfo.h
===================================================================
--- lib/Target/SystemZ/SystemZRegisterInfo.h
+++ lib/Target/SystemZ/SystemZRegisterInfo.h
@@ -42,6 +42,13 @@
     return &SystemZ::ADDR64BitRegClass;
   }
 
+  void getRegAllocationHints(unsigned VirtReg,
+                             ArrayRef<MCPhysReg> Order,
+                             SmallVectorImpl<MCPhysReg> &Hints,
+                             const MachineFunction &MF,
+                             const VirtRegMap *VRM,
+                             const LiveRegMatrix *Matrix) const override;
+
   // Override TargetRegisterInfo.h.
   bool requiresRegisterScavenging(const MachineFunction &MF) const override {
     return true;
Index: lib/Target/SystemZ/SystemZRegisterInfo.cpp
===================================================================
--- lib/Target/SystemZ/SystemZRegisterInfo.cpp
+++ lib/Target/SystemZ/SystemZRegisterInfo.cpp
@@ -10,6 +10,7 @@
 #include "SystemZRegisterInfo.h"
 #include "SystemZInstrInfo.h"
 #include "SystemZSubtarget.h"
+#include "llvm/ADT/SmallSet.h"
 #include "llvm/CodeGen/MachineInstrBuilder.h"
 #include "llvm/CodeGen/MachineRegisterInfo.h"
 #include "llvm/Target/TargetFrameLowering.h"
@@ -22,6 +23,65 @@
 SystemZRegisterInfo::SystemZRegisterInfo()
     : SystemZGenRegisterInfo(SystemZ::R14D) {}
 
+void
+SystemZRegisterInfo::getRegAllocationHints(unsigned VirtReg,
+                                           ArrayRef<MCPhysReg> Order,
+                                           SmallVectorImpl<MCPhysReg> &Hints,
+                                           const MachineFunction &MF,
+                                           const VirtRegMap *VRM,
+                                           const LiveRegMatrix *Matrix) const {
+  const MachineRegisterInfo *MRI = &MF.getRegInfo();
+  const TargetRegisterInfo *TRI = MF.getSubtarget().getRegisterInfo();
+
+  // Hint all physregs that are connected with VirtReg via COPYs.
+  const TargetRegisterClass *RC = MRI->getRegClass(VirtReg);
+  SmallSet<unsigned,4> ConnectedPhysRegs;
+  for (auto &Use : MRI->use_instructions(VirtReg)) {
+    if (Use.isCopy()) {
+      unsigned PhysReg = 0;
+      MachineOperand &DstMO = Use.getOperand(0);
+      MachineOperand &SrcMO = Use.getOperand(1);
+      MachineOperand *VirtRegMO = nullptr;
+      // Get the connected physreg, if any.
+      if (TRI->isPhysicalRegister(DstMO.getReg())) {
+        PhysReg = DstMO.getReg();
+        if (DstMO.getSubReg())
+          PhysReg = TRI->getSubReg(PhysReg, DstMO.getSubReg());
+        VirtRegMO = &SrcMO;
+      } else if (TRI->isPhysicalRegister(SrcMO.getReg())) {
+        PhysReg = SrcMO.getReg();
+        if (SrcMO.getSubReg())
+          PhysReg = TRI->getSubReg(PhysReg, SrcMO.getSubReg());
+        VirtRegMO = &DstMO;
+      }
+      if (!PhysReg)
+        continue;
+
+      if (RC->contains(PhysReg)) {
+        ConnectedPhysRegs.insert(PhysReg);
+        continue;
+      }
+
+      // Check if the subreg index match so that a super register of PhysReg
+      // could be hinted.
+      if (VirtRegMO->getSubReg() != SystemZ::NoSubRegister) {
+        if (unsigned SuperReg =
+            TRI->getMatchingSuperReg(PhysReg, VirtRegMO->getSubReg(), RC))
+          ConnectedPhysRegs.insert(SuperReg);
+      }
+    }
+  }
+
+  if (!ConnectedPhysRegs.empty()) {
+    // Add the connected physregs sorted by the allocation order.
+    for (MCPhysReg Reg : Order)
+      if (ConnectedPhysRegs.count(Reg) && !MRI->isReserved(Reg))
+        Hints.push_back(Reg);
+  }
+
+  TargetRegisterInfo::getRegAllocationHints(VirtReg, Order, Hints, MF, VRM);
+}
+
 const MCPhysReg *
 SystemZRegisterInfo::getCalleeSavedRegs(const MachineFunction *MF) const {
   if (MF->getSubtarget().getTargetLowering()->supportSwiftError() &&
Index: test/CodeGen/SystemZ/call-args-coalesce.mir
===================================================================
--- /dev/null
+++ test/CodeGen/SystemZ/call-args-coalesce.mir
@@ -0,0 +1,45 @@
+# RUN: llc -mtriple=s390x-linux-gnu -start-before=greedy %s -o - | FileCheck %s
+# Test that %r2d is copied directly to %r1d
+
+--- |
+  
+  define void @f5(void (i32, i32, i32, i32)* %foo) {
+    tail call void %foo(i32 1, i32 2, i32 3, i32 4)
+    ret void
+  }
+  
+  ; Function Attrs: nounwind
+  declare void @llvm.stackprotector(i8*, i8**) #0
+  
+  attributes #0 = { nounwind }
+
+...
+
+# CHECK: lgr     %r1, %r2
+# CHECK-NOT: lgr
+
+---
+name:            f5
+alignment:       2
+tracksRegLiveness: true
+registers:       
+  - { id: 0, class: gr64bit }
+  - { id: 1, class: gr32bit }
+  - { id: 2, class: gr32bit }
+  - { id: 3, class: gr32bit }
+  - { id: 4, class: gr32bit }
+liveins:         
+  - { reg: '%r2d', virtual-reg: '%0' }
+body:             |
+  bb.0 (%ir-block.0):
+    liveins: %r2d
+  
+    %0 = COPY %r2d
+    %r2l = LHI 1
+    %r3l = LHI 2
+    %r4l = LHI 3
+    %r5l = LHI 4
+    %r1d = COPY %0
+    CallBR csr_systemz, implicit %r1d, implicit %r2l, implicit killed %r3l, implicit killed %r4l, implicit killed %r5l
+
+...