[x86] Teach the shrink-wrapping hooks to do the proper thing with Win64.

Win64 has some strict requirements for the epilogue. As a result, we disable
shrink-wrapping for Win64 unless the block that gets the epilogue is already an
exit block.

Fixes PR24193.

llvm-svn: 252088

1 files changed, 8 insertions, 0 deletions

diff --git a/llvm/lib/Target/X86/X86FrameLowering.cpp b/llvm/lib/Target/X86/X86FrameLowering.cpp
index 7b7f0daf12b..ee866fa45c3 100644
--- a/llvm/lib/Target/X86/X86FrameLowering.cpp
+++ b/llvm/lib/Target/X86/X86FrameLowering.cpp
@@ -2184,6 +2184,14 @@ eliminateCallFramePseudoInstr(MachineFunction &MF, MachineBasicBlock &MBB,
 bool X86FrameLowering::canUseAsEpilogue(const MachineBasicBlock &MBB) const {
   assert(MBB.getParent() && "Block is not attached to a function!");
 
+  // Win64 has strict requirements in terms of epilogue and we are
+  // not taking a chance at messing with them.
+  // I.e., unless this block is already an exit block, we can't use
+  // it as an epilogue.
+  if (MBB.getParent()->getSubtarget<X86Subtarget>().isTargetWin64() &&
+      !MBB.succ_empty() && !MBB.isReturnBlock())
+    return false;
+
   if (canUseLEAForSPInEpilogue(*MBB.getParent()))
     return true;