Revert [Windows] Disable TrapUnreachable for Win64, add SEH_NoReturn

This reverts r370525 (git commit 0bb1630685fba255fa93def92603f064c2ffd203)
Also reverts r370543 (git commit 185ddc08eed6542781040b8499ef7ad15c8ae9f4)

The approach I took only works for functions marked `noreturn`. In
general, a call that is not known to be noreturn may be followed by
unreachable for other reasons. For example, there could be multiple call
sites to a function that throws sometimes, and at some call sites, it is
known to always throw, so it is followed by unreachable. We need to
insert an `int3` in these cases to pacify the Windows unwinder.

I think this probably deserves its own standalone, Win64-only fixup pass
that runs after block placement. Implementing that will take some time,
so let's revert to TrapUnreachable in the mean time.

llvm-svn: 370829

1 files changed, 1 insertions, 1 deletions

diff --git a/llvm/lib/Target/X86/X86FrameLowering.cpp b/llvm/lib/Target/X86/X86FrameLowering.cpp
index 681a618e2d5..e1ed5aa5abc 100644
--- a/llvm/lib/Target/X86/X86FrameLowering.cpp
+++ b/llvm/lib/Target/X86/X86FrameLowering.cpp
@@ -2558,7 +2558,7 @@ bool blockEndIsUnreachable(const MachineBasicBlock &MBB,
              MBB.succ_begin(), MBB.succ_end(),
              [](const MachineBasicBlock *Succ) { return Succ->isEHPad(); }) &&
          std::all_of(MBBI, MBB.end(), [](const MachineInstr &MI) {
-           return MI.isMetaInstruction() || MI.getOpcode() == X86::SEH_NoReturn;
+           return MI.isMetaInstruction();
          });
 }