Patch by Vadim Chugunov

Win64 stack unwinder gets confused when execution flow "falls through" after
a call to 'noreturn' function. This fixes the "missing epilogue" problem by 
emitting a trap instruction for IR 'unreachable' on x86_x64-pc-windows.

A secondary use for it would be for anyone wanting to make double-sure that
'noreturn' functions, indeed, do not return.

llvm-svn: 206684

1 files changed, 7 insertions, 0 deletions

diff --git a/llvm/lib/Target/X86/X86TargetMachine.cpp b/llvm/lib/Target/X86/X86TargetMachine.cpp
index 6f09ccf0cec..cb5ab0dd502 100644
--- a/llvm/lib/Target/X86/X86TargetMachine.cpp
+++ b/llvm/lib/Target/X86/X86TargetMachine.cpp
@@ -108,6 +108,13 @@ X86TargetMachine::X86TargetMachine(const Target &T, StringRef TT,
   if (Options.FloatABIType == FloatABI::Default)
     this->Options.FloatABIType = FloatABI::Hard;
 
+  // Windows stack unwinder gets confused when execution flow "falls through"
+  // after a call to 'noreturn' function.
+  // To prevent that, we emit a trap for 'unreachable' IR instructions.
+  // (which on X86, happens to be the 'ud2' instruction)
+  if (Subtarget.isTargetWin64())
+    this->Options.TrapUnreachable = true;
+
   initAsmInfo();
 }