Index: lib/Target/X86/X86FrameLowering.cpp
===================================================================
--- lib/Target/X86/X86FrameLowering.cpp
+++ lib/Target/X86/X86FrameLowering.cpp
@@ -1213,30 +1213,34 @@
     bool isEAXAlive = isEAXLiveIn(MBB);
 
     if (isEAXAlive) {
-      // Sanity check that EAX is not livein for this function.
-      // It should not be, so throw an assert.
-      assert(!Is64Bit && "EAX is livein in x64 case!");
-
-      // Save EAX
-      BuildMI(MBB, MBBI, DL, TII.get(X86::PUSH32r))
-        .addReg(X86::EAX, RegState::Kill)
-        .setMIFlag(MachineInstr::FrameSetup);
+      if (Is64Bit) {
+        // Save RAX
+        BuildMI(MBB, MBBI, DL, TII.get(X86::PUSH64r))
+          .addReg(X86::RAX, RegState::Kill)
+          .setMIFlag(MachineInstr::FrameSetup);
+      } else {
+        // Save EAX
+        BuildMI(MBB, MBBI, DL, TII.get(X86::PUSH32r))
+          .addReg(X86::EAX, RegState::Kill)
+          .setMIFlag(MachineInstr::FrameSetup);
+      }
     }
 
     if (Is64Bit) {
       // Handle the 64-bit Windows ABI case where we need to call __chkstk.
       // Function prologue is responsible for adjusting the stack pointer.
-      if (isUInt<32>(NumBytes)) {
+      int Alloc = isEAXAlive ? NumBytes - 8 : NumBytes;
+      if (isUInt<32>(Alloc)) {
         BuildMI(MBB, MBBI, DL, TII.get(X86::MOV32ri), X86::EAX)
-            .addImm(NumBytes)
+            .addImm(Alloc)
             .setMIFlag(MachineInstr::FrameSetup);
-      } else if (isInt<32>(NumBytes)) {
+      } else if (isInt<32>(Alloc)) {
         BuildMI(MBB, MBBI, DL, TII.get(X86::MOV64ri32), X86::RAX)
-            .addImm(NumBytes)
+            .addImm(Alloc)
             .setMIFlag(MachineInstr::FrameSetup);
       } else {
         BuildMI(MBB, MBBI, DL, TII.get(X86::MOV64ri), X86::RAX)
-            .addImm(NumBytes)
+            .addImm(Alloc)
             .setMIFlag(MachineInstr::FrameSetup);
       }
     } else {
@@ -1251,10 +1255,14 @@
     emitStackProbe(MF, MBB, MBBI, DL, true);
 
     if (isEAXAlive) {
-      // Restore EAX
-      MachineInstr *MI =
-          addRegOffset(BuildMI(MF, DL, TII.get(X86::MOV32rm), X86::EAX),
-                       StackPtr, false, NumBytes - 4);
+      // Restore RAX/EAX
+      MachineInstr *MI;
+      if (Is64Bit)
+        MI = addRegOffset(BuildMI(MF, DL, TII.get(X86::MOV64rm), X86::RAX),
+                          StackPtr, false, NumBytes - 8);
+      else
+        MI = addRegOffset(BuildMI(MF, DL, TII.get(X86::MOV32rm), X86::EAX),
+                          StackPtr, false, NumBytes - 4);
       MI->setFlag(MachineInstr::FrameSetup);
       MBB.insert(MBBI, MI);
     }
Index: test/CodeGen/X86/shrink-wrap-chkstk-x86_64.ll
===================================================================
--- /dev/null
+++ test/CodeGen/X86/shrink-wrap-chkstk-x86_64.ll
@@ -0,0 +1,36 @@
+; RUN: llc -mtriple=x86_64-windows-gnu -exception-model=dwarf < %s | FileCheck %s
+
+%struct.A = type { [4096 x i8] }
+
+@a = common global i32 0, align 4
+@b = common global i32 0, align 4
+
+define void @fn1() nounwind uwtable {
+entry:
+  %ctx = alloca %struct.A, align 1
+  %0 = load i32, i32* @a, align 4
+  %tobool = icmp eq i32 %0, 0
+  %div = sdiv i32 %0, 6
+  %cond = select i1 %tobool, i32 %div, i32 %0
+  store i32 %cond, i32* @b, align 4
+  %1 = getelementptr inbounds %struct.A, %struct.A* %ctx, i64 0, i32 0, i64 0
+  call void @llvm.lifetime.start.p0i8(i64 4096, i8* nonnull %1)
+  %2 = ptrtoint %struct.A* %ctx to i64
+  %3 = trunc i64 %2 to i32
+  call void @fn2(i32 %3)
+  call void @llvm.lifetime.end.p0i8(i64 4096, i8* nonnull %1)
+  ret void
+}
+
+declare void @fn2(i32)
+declare void @llvm.lifetime.start.p0i8(i64, i8* nocapture)
+declare void @llvm.lifetime.end.p0i8(i64, i8* nocapture)
+
+; CHECK-LABEL: fn1:
+; CHECK: pushq %rax
+; CHECK: movl $4128, %eax
+; CHECK: callq ___chkstk_ms
+; CHECK: subq %rax, %rsp
+; CHECK: movq 4128(%rsp), %rax
+
+; CHECK: addq $4136, %rsp