[Windows] Replace TrapUnreachable with an int3 insertion pass

This is an alternative to D66980, which was reverted. Instead of
inserting a pseudo instruction that optionally expands to nothing, add a
pass that inserts int3 when appropriate after basic block layout.

Reviewers: hans

Differential Revision: https://reviews.llvm.org/D67201

llvm-svn: 371466

1 files changed, 10 insertions, 11 deletions

diff --git a/llvm/lib/Target/X86/X86TargetMachine.cpp b/llvm/lib/Target/X86/X86TargetMachine.cpp
index d33a7a0b963..f6184a3c1f1 100644
--- a/llvm/lib/Target/X86/X86TargetMachine.cpp
+++ b/llvm/lib/Target/X86/X86TargetMachine.cpp
@@ -219,17 +219,9 @@ X86TargetMachine::X86TargetMachine(const Target &T, const Triple &TT,
           getEffectiveX86CodeModel(CM, JIT, TT.getArch() == Triple::x86_64),
           OL),
       TLOF(createTLOF(getTargetTriple())) {
-  // 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)
   // On PS4, the "return address" of a 'noreturn' call must still be within
   // the calling function, and TrapUnreachable is an easy way to get that.
-  // The check here for 64-bit windows is a bit icky, but as we're unlikely
-  // to ever want to mix 32 and 64-bit windows code in a single module
-  // this should be fine.
-  if ((TT.isOSWindows() && TT.getArch() == Triple::x86_64) || TT.isPS4() ||
-      TT.isOSBinFormatMachO()) {
+  if (TT.isPS4() || TT.isOSBinFormatMachO()) {
     this->Options.TrapUnreachable = true;
     this->Options.NoTrapAfterNoreturn = TT.isOSBinFormatMachO();
   }
@@ -518,12 +510,19 @@ void X86PassConfig::addPreEmitPass() {
 }
 
 void X86PassConfig::addPreEmitPass2() {
+  const Triple &TT = TM->getTargetTriple();
+  const MCAsmInfo *MAI = TM->getMCAsmInfo();
+
   addPass(createX86RetpolineThunksPass());
+
+  // Insert extra int3 instructions after trailing call instructions to avoid
+  // issues in the unwinder.
+  if (TT.isOSWindows() && TT.getArch() == Triple::x86_64)
+    addPass(createX86AvoidTrailingCallPass());
+
   // Verify basic block incoming and outgoing cfa offset and register values and
   // correct CFA calculation rule where needed by inserting appropriate CFI
   // instructions.
-  const Triple &TT = TM->getTargetTriple();
-  const MCAsmInfo *MAI = TM->getMCAsmInfo();
   if (!TT.isOSDarwin() &&
       (!TT.isOSWindows() ||
        MAI->getExceptionHandlingType() == ExceptionHandling::DwarfCFI))