[AArch64] [Windows] Trap after noreturn calls.

Like the comment says, this isn't the most efficient fix in terms of
codesize, but it works.

Differential Revision: https://reviews.llvm.org/D54129

llvm-svn: 346358

lib/Target/AArch64/AArch64TargetMachine.cpp

@@ -263,6 +263,16 @@ AArch64TargetMachine::AArch64TargetMachine(const Target &T, const Triple &TT,
     this->Options.NoTrapAfterNoreturn = true;
   }
 
+  if (TT.isOSWindows()) {
+    // Unwinding can get confused if the last instruction in an
+    // exception-handling region (function, funclet, try block, etc.)
+    // is a call.
+    //
+    // FIXME: We could elide the trap if the next instruction would be in
+    // the same region anyway.
+    this->Options.TrapUnreachable = true;
+  }
+
   // Enable GlobalISel at or below EnableGlobalISelAt0.
   if (getOptLevel() <= EnableGlobalISelAtO)
     setGlobalISel(true);

test/CodeGen/AArch64/windows-trap.ll

@@ -0,0 +1,17 @@
+; RUN: llc -mtriple=aarch64-win32 %s -o - | FileCheck %s
+
+declare void @callee() noreturn
+
+; Make sure the call isn't the last instruction in the function; if it is,
+; unwinding may break.
+;
+; (The instruction after the call doesn't have to be anything in particular,
+; but trapping has the nice side-effect of catching bugs.)
+
+define void @test_unreachable() {
+; CHECK-LABEL: test_unreachable:
+; CHECK: bl      callee
+; CHECK-NEXT: brk #0x1
+  call void @callee() noreturn
+  unreachable
+}