[WinEH] Try to make the MachineFunction CFG more accurate

This avoids emitting code for unreachable landingpad blocks that contain
calls to llvm.eh.actions and indirectbr.

It's also a first step towards unifying the SEH and WinEH lowering
codepaths. I'm keeping the old fan-in lowering of SEH around until the
preparation version works well enough that we can switch over without
breaking existing users.

llvm-svn: 235037

1 files changed, 7 insertions, 3 deletions

diff --git a/llvm/lib/CodeGen/AsmPrinter/Win64Exception.cpp b/llvm/lib/CodeGen/AsmPrinter/Win64Exception.cpp
index 0d422d83e2d..f89d36455f4 100644
--- a/llvm/lib/CodeGen/AsmPrinter/Win64Exception.cpp
+++ b/llvm/lib/CodeGen/AsmPrinter/Win64Exception.cpp
@@ -108,8 +108,13 @@ void Win64Exception::endFunction(const MachineFunction *MF) {
   if (!shouldEmitPersonality && !shouldEmitMoves)
     return;
 
-  // Map all labels and get rid of any dead landing pads.
-  MMI->TidyLandingPads();
+  EHPersonality Per = MMI->getPersonalityType();
+
+  // Get rid of any dead landing pads if we're not using a Windows EH scheme. In
+  // Windows EH schemes, the landing pad is not actually reachable. It only
+  // exists so that we can emit the right table data.
+  if (!isMSVCEHPersonality(Per))
+    MMI->TidyLandingPads();
 
   if (shouldEmitPersonality) {
     Asm->OutStreamer.PushSection();
@@ -119,7 +124,6 @@ void Win64Exception::endFunction(const MachineFunction *MF) {
 
     // Emit the tables appropriate to the personality function in use. If we
     // don't recognize the personality, assume it uses an Itanium-style LSDA.
-    EHPersonality Per = MMI->getPersonalityType();
     if (Per == EHPersonality::MSVC_Win64SEH)
       emitCSpecificHandlerTable();
     else if (Per == EHPersonality::MSVC_CXX)