[WinEH] Don't let UnwindHelp alias the return address

On top of that, don't bother allocating and initializing UnwindHelp if
we don't have any funclets. Currently we always use RBP as our frame
pointer when funclets are present, so this change makes it impossible to
come here without any fixed stack objects.

Fixes PR25533.

llvm-svn: 253245

1 files changed, 6 insertions, 6 deletions

diff --git a/llvm/lib/Target/X86/X86FrameLowering.cpp b/llvm/lib/Target/X86/X86FrameLowering.cpp
index 3c557fe8a11..72baa078661 100644
--- a/llvm/lib/Target/X86/X86FrameLowering.cpp
+++ b/llvm/lib/Target/X86/X86FrameLowering.cpp
@@ -2662,17 +2662,17 @@ void X86FrameLowering::processFunctionBeforeFrameFinalized(
   // If this function isn't doing Win64-style C++ EH, we don't need to do
   // anything.
   const Function *Fn = MF.getFunction();
-  if (!STI.is64Bit() || !Fn->hasPersonalityFn() ||
-      classifyEHPersonality(MF.getFunction()->getPersonalityFn()) !=
-          EHPersonality::MSVC_CXX)
+  if (!STI.is64Bit() || !MF.getMMI().hasEHFunclets() ||
+      classifyEHPersonality(Fn->getPersonalityFn()) != EHPersonality::MSVC_CXX)
     return;
 
   // Win64 C++ EH needs to allocate the UnwindHelp object at some fixed offset
   // relative to RSP after the prologue.  Find the offset of the last fixed
-  // object, so that we can allocate a slot immediately following it. Fixed
-  // objects have negative frame indices.
+  // object, so that we can allocate a slot immediately following it. If there
+  // were no fixed objects, use offset -SlotSize, which is immediately after the
+  // return address. Fixed objects have negative frame indices.
   MachineFrameInfo *MFI = MF.getFrameInfo();
-  int64_t MinFixedObjOffset = 0;
+  int64_t MinFixedObjOffset = -SlotSize;
   for (int I = MFI->getObjectIndexBegin(); I < 0; ++I)
     MinFixedObjOffset = std::min(MinFixedObjOffset, MFI->getObjectOffset(I));