Index: llvm/lib/Target/X86/X86FrameLowering.cpp
===================================================================
--- llvm/lib/Target/X86/X86FrameLowering.cpp
+++ llvm/lib/Target/X86/X86FrameLowering.cpp
@@ -1349,15 +1349,12 @@
   // to determine the end of the prologue.
   DebugLoc DL;
 
-  // Add RETADDR move area to callee saved frame size.
-  int TailCallReturnAddrDelta = X86FI->getTCReturnAddrDelta();
-  if (TailCallReturnAddrDelta && IsWin64Prologue)
+  // Space reserved for stack-based arguments when making a (ABI-guaranteed)
+  // tail call.
+  unsigned TailCallArgReserveSize = -X86FI->getTCReturnAddrDelta();
+  if (TailCallArgReserveSize  && IsWin64Prologue)
     report_fatal_error("Can't handle guaranteed tail call under win64 yet");
 
-  if (TailCallReturnAddrDelta < 0)
-    X86FI->setCalleeSavedFrameSize(
-      X86FI->getCalleeSavedFrameSize() - TailCallReturnAddrDelta);
-
   const bool EmitStackProbeCall =
       STI.getTargetLowering()->hasStackProbeSymbol(MF);
   unsigned StackProbeSize = STI.getTargetLowering()->getStackProbeSize(MF);
@@ -1391,7 +1388,8 @@
       !EmitStackProbeCall &&                   // No stack probes.
       !MFI.hasCopyImplyingStackAdjustment() && // Don't push and pop.
       !MF.shouldSplitStack()) {                // Regular stack
-    uint64_t MinSize = X86FI->getCalleeSavedFrameSize();
+    uint64_t MinSize =
+        X86FI->getCalleeSavedFrameSize() - X86FI->getTCReturnAddrDelta();
     if (HasFP) MinSize += SlotSize;
     X86FI->setUsesRedZone(MinSize > 0 || StackSize > 0);
     StackSize = std::max(MinSize, StackSize > 128 ? StackSize - 128 : 0);
@@ -1401,8 +1399,8 @@
   // Insert stack pointer adjustment for later moving of return addr.  Only
   // applies to tail call optimized functions where the callee argument stack
   // size is bigger than the callers.
-  if (TailCallReturnAddrDelta < 0) {
-    BuildStackAdjustment(MBB, MBBI, DL, TailCallReturnAddrDelta,
+  if (TailCallArgReserveSize != 0) {
+    BuildStackAdjustment(MBB, MBBI, DL, -(int)TailCallArgReserveSize,
                          /*InEpilogue=*/false)
         .setMIFlag(MachineInstr::FrameSetup);
   }
@@ -1451,7 +1449,8 @@
     if (X86FI->getRestoreBasePointer())
       FrameSize += SlotSize;
 
-    NumBytes = FrameSize - X86FI->getCalleeSavedFrameSize();
+    NumBytes = FrameSize -
+               (X86FI->getCalleeSavedFrameSize() + TailCallArgReserveSize);
 
     // Callee-saved registers are pushed on stack before the stack is realigned.
     if (TRI->hasStackRealignment(MF) && !IsWin64Prologue)
@@ -1554,7 +1553,8 @@
     }
   } else {
     assert(!IsFunclet && "funclets without FPs not yet implemented");
-    NumBytes = StackSize - X86FI->getCalleeSavedFrameSize();
+    NumBytes = StackSize -
+               (X86FI->getCalleeSavedFrameSize() + TailCallArgReserveSize);
   }
 
   // Update the offset adjustment, which is mainly used by codeview to translate
@@ -2011,6 +2011,7 @@
   uint64_t StackSize = MFI.getStackSize();
   uint64_t MaxAlign = calculateMaxStackAlign(MF);
   unsigned CSSize = X86FI->getCalleeSavedFrameSize();
+  unsigned TailCallArgReserveSize = -X86FI->getTCReturnAddrDelta();
   bool HasFP = hasFP(MF);
   uint64_t NumBytes = 0;
 
@@ -2024,14 +2025,14 @@
   } else if (HasFP) {
     // Calculate required stack adjustment.
     uint64_t FrameSize = StackSize - SlotSize;
-    NumBytes = FrameSize - CSSize;
+    NumBytes = FrameSize - CSSize - TailCallArgReserveSize;
 
     // Callee-saved registers were pushed on stack before the stack was
     // realigned.
     if (TRI->hasStackRealignment(MF) && !IsWin64Prologue)
       NumBytes = alignTo(FrameSize, MaxAlign);
   } else {
-    NumBytes = StackSize - CSSize;
+    NumBytes = StackSize - CSSize - TailCallArgReserveSize;
   }
   uint64_t SEHStackAllocAmt = NumBytes;
 
@@ -2098,7 +2099,6 @@
 
   if (MBBI != MBB.end())
     DL = MBBI->getDebugLoc();
-
   // If there is an ADD32ri or SUB32ri of ESP immediately before this
   // instruction, merge the two instructions.
   if (NumBytes || MFI.hasVarSizedObjects())
@@ -2143,7 +2143,8 @@
     if (!hasFP(MF) && NeedsDwarfCFI) {
       // Define the current CFA rule to use the provided offset.
       BuildCFI(MBB, MBBI, DL,
-               MCCFIInstruction::cfiDefCfaOffset(nullptr, CSSize + SlotSize));
+               MCCFIInstruction::cfiDefCfaOffset(
+                   nullptr, CSSize + TailCallArgReserveSize + SlotSize));
     }
     --MBBI;
   }
@@ -2226,7 +2227,6 @@
   const X86MachineFunctionInfo *X86FI = MF.getInfo<X86MachineFunctionInfo>();
   unsigned CSSize = X86FI->getCalleeSavedFrameSize();
   uint64_t StackSize = MFI.getStackSize();
-  bool HasFP = hasFP(MF);
   bool IsWin64Prologue = MF.getTarget().getMCAsmInfo()->usesWindowsCFI();
   int64_t FPDelta = 0;
 
@@ -2262,39 +2262,27 @@
            "FPDelta isn't aligned per the Win64 ABI!");
   }
 
-
-  if (TRI->hasBasePointer(MF)) {
-    assert(HasFP && "VLAs and dynamic stack realign, but no FP?!");
-    if (FI < 0) {
-      // Skip the saved EBP.
-      return StackOffset::getFixed(Offset + SlotSize + FPDelta);
-    } else {
-      assert(isAligned(MFI.getObjectAlign(FI), -(Offset + StackSize)));
-      return StackOffset::getFixed(Offset + StackSize);
-    }
-  } else if (TRI->hasStackRealignment(MF)) {
-    if (FI < 0) {
-      // Skip the saved EBP.
-      return StackOffset::getFixed(Offset + SlotSize + FPDelta);
-    } else {
-      assert(isAligned(MFI.getObjectAlign(FI), -(Offset + StackSize)));
-      return StackOffset::getFixed(Offset + StackSize);
-    }
-    // FIXME: Support tail calls
-  } else {
-    if (!HasFP)
-      return StackOffset::getFixed(Offset + StackSize);
-
-    // Skip the saved EBP.
+  if (FrameReg == TRI->getFramePtr()) {
+    // Skip saved EBP/RBP
     Offset += SlotSize;
 
+    // Account for restricted Windows prologue.
+    Offset += FPDelta;
+
     // Skip the RETADDR move area
     int TailCallReturnAddrDelta = X86FI->getTCReturnAddrDelta();
     if (TailCallReturnAddrDelta < 0)
       Offset -= TailCallReturnAddrDelta;
+
+    return StackOffset::getFixed(Offset);
   }
 
-  return StackOffset::getFixed(Offset + FPDelta);
+  // FrameReg is either the stack pointer or a base pointer. But the base is
+  // located at the end of the statically known StackSize so the distinction
+  // doesn't really matter.
+  if (TRI->hasStackRealignment(MF) || TRI->hasBasePointer(MF))
+    assert(isAligned(MFI.getObjectAlign(FI), -(Offset + StackSize)));
+  return StackOffset::getFixed(Offset + StackSize);
 }
 
 int X86FrameLowering::getWin64EHFrameIndexRef(const MachineFunction &MF, int FI,
Index: llvm/test/CodeGen/X86/swifttail-realign.ll
===================================================================
--- /dev/null
+++ llvm/test/CodeGen/X86/swifttail-realign.ll
@@ -0,0 +1,29 @@
+; RUN: llc -mtriple=x86_64-linux-gnu %s -o - | FileCheck %s
+
+declare swifttailcc void @callee([6 x i64], i64, i64)
+
+@var = external global i8*
+
+define swifttailcc void @caller(i64 %n) {
+; CHECK-LABEL: caller:
+; CHECK: subq $16, %rsp
+; CHECK: pushq %rbp
+; CHECK: movq %rsp, %rbp
+; CHECK: pushq %rbx
+; CHECK: andq $-32, %rsp
+; [... don't really care what happens to rsp to allocate %ptr ...]
+; CHECK: movq %24(%rbp), [[RETADDR:%.*]]
+; CHECK: movq [[RETADDR]], 8(%rbp)
+; CHECK: movq $42, 16(%rbp)
+; CHECK: movq $0, 24(%rbp)
+; CHECK: leaq -8(%rbp), %rsp
+; CHECK: popq %rbx
+; CHECK: popq %rbp
+; CHECK: jmp callee
+
+  call void asm sideeffect "", "~{rbx}"()
+  %ptr = alloca i8, i64 %n, align 32
+  store i8* %ptr, i8** @var
+  tail call swifttailcc void @callee([6 x i64] undef, i64 42, i64 0)
+  ret void
+}