Index: llvm/lib/Target/AArch64/AArch64FrameLowering.cpp
===================================================================
--- llvm/lib/Target/AArch64/AArch64FrameLowering.cpp
+++ llvm/lib/Target/AArch64/AArch64FrameLowering.cpp
@@ -579,6 +579,12 @@
          !F.hasFnAttribute("no-stack-arg-probe");
 }
 
+static bool needsWinCFI(const MachineFunction &MF) {
+  const Function &F = MF.getFunction();
+  return MF.getTarget().getMCAsmInfo()->usesWindowsCFI() &&
+         F.needsUnwindTableEntry();
+}
+
 bool AArch64FrameLowering::shouldCombineCSRLocalStackBump(
     MachineFunction &MF, uint64_t StackBumpBytes) const {
   AArch64FunctionInfo *AFI = MF.getInfo<AArch64FunctionInfo>();
@@ -589,6 +595,18 @@
   if (AFI->getLocalStackSize() == 0)
     return false;
 
+  // For WinCFI, if optimizing for size, prefer to not combine the stack bump
+  // (to force a stp with predecrement) to match the packed unwind format,
+  // provided that there actually are any callee saved registers to merge the
+  // decrement with.
+  // This is potentially marginally slower, but allows using the packed
+  // unwind format for functions that both have a local area and callee saved
+  // registers. Using the packed unwind format notably reduces the size of
+  // the unwind info.
+  if (needsWinCFI(MF) && AFI->getCalleeSavedStackSize() > 0 &&
+      MF.getFunction().hasOptSize())
+    return false;
+
   // 512 is the maximum immediate for stp/ldp that will be used for
   // callee-save save/restores
   if (StackBumpBytes >= 512 || windowsRequiresStackProbe(MF, StackBumpBytes))
@@ -982,12 +1000,6 @@
   //
 }
 
-static bool needsWinCFI(const MachineFunction &MF) {
-  const Function &F = MF.getFunction();
-  return MF.getTarget().getMCAsmInfo()->usesWindowsCFI() &&
-         F.needsUnwindTableEntry();
-}
-
 static bool isTargetWindows(const MachineFunction &MF) {
   return MF.getSubtarget<AArch64Subtarget>().isTargetWindows();
 }
Index: llvm/test/CodeGen/AArch64/wineh-frame-predecrement.mir
===================================================================
--- /dev/null
+++ llvm/test/CodeGen/AArch64/wineh-frame-predecrement.mir
@@ -0,0 +1,70 @@
+# RUN: llc -o - %s -mtriple=aarch64-windows -start-before=prologepilog \
+# RUN:   -stop-after=prologepilog | FileCheck %s
+
+# Check that the callee-saved registers are saved starting with a STP
+# with predecrement, followed by a separate stack adjustment later,
+# if the optsize attribute is set.
+
+# CHECK:      early-clobber $sp = frame-setup STPXpre killed $x19, killed $x20, $sp, -2
+# CHECK-NEXT: frame-setup SEH_SaveRegP_X 19, 20, -16
+# CHECK-NEXT: $sp = frame-setup SUBXri $sp, 16, 0
+# CHECK-NEXT: frame-setup SEH_StackAlloc 16
+# CHECK-NEXT: frame-setup SEH_PrologEnd
+
+--- |
+
+  define dso_local i32 @func(i32 %a) optsize { ret i32 %a }
+
+...
+---
+name:            func
+alignment:       4
+exposesReturnsTwice: false
+legalized:       false
+regBankSelected: false
+selected:        false
+failedISel:      false
+tracksRegLiveness: true
+hasWinCFI:       false
+registers:       []
+liveins:         []
+frameInfo:
+  isFrameAddressTaken: false
+  isReturnAddressTaken: false
+  hasStackMap:     false
+  hasPatchPoint:   false
+  stackSize:       0
+  offsetAdjustment: 0
+  maxAlignment:    4
+  adjustsStack:    false
+  hasCalls:        false
+  stackProtector:  ''
+  maxCallFrameSize: 0
+  cvBytesOfCalleeSavedRegisters: 0
+  hasOpaqueSPAdjustment: false
+  hasVAStart:      false
+  hasMustTailInVarArgFunc: false
+  localFrameSize:  4
+  savePoint:       ''
+  restorePoint:    ''
+fixedStack:      []
+stack:
+  - { id: 0, name: '', type: default, offset: 0, size: 4, alignment: 4,
+      stack-id: default, callee-saved-register: '', callee-saved-restored: true,
+      local-offset: -4, debug-info-variable: '', debug-info-expression: '',
+      debug-info-location: '' }
+callSites:       []
+constants:       []
+machineFunctionInfo: {}
+body:             |
+  bb.0:
+    liveins: $x0, $x19, $x20
+
+    renamable $x8 = ADDXri %stack.0, 0, 0
+    $x19 = ADDXrr $x0, $x8
+    $x20 = ADDXrr $x19, $x0
+    $x0 = ADDXrr $x0, killed $x20
+
+    RET_ReallyLR
+
+...