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, 0 insertions, 3 deletions

diff --git a/llvm/lib/Target/X86/X86ISelLowering.h b/llvm/lib/Target/X86/X86ISelLowering.h
index e8255da2393..05e4f16fc49 100644
--- a/llvm/lib/Target/X86/X86ISelLowering.h
+++ b/llvm/lib/Target/X86/X86ISelLowering.h
@@ -531,9 +531,6 @@ namespace llvm {
       // Windows's _chkstk call to do stack probing.
       WIN_ALLOCA,
 
-      // Expands to int3 or nothing, depending on basic block layout.
-      SEH_NORETURN,
-
       // For allocating variable amounts of stack space when using
       // segmented stacks. Check if the current stacklet has enough space, and
       // falls back to heap allocation if not.