Add a Windows EH preparation pass that zaps resumes

If the personality is not a recognized MSVC personality function, this
pass delegates to the dwarf EH preparation pass. This chaining supports
people on *-windows-itanium or *-windows-gnu targets.

Currently this recognizes some personalities used by MSVC and turns
resume instructions into traps to avoid link errors.  Even if cleanups
are not used in the source program, LLVM requires the frontend to emit a
code path that resumes unwinding after an exception.  Clang does this,
and we get unreachable resume instructions. PR20300 covers cleaning up
these unreachable calls to resume.

Reviewers: majnemer

Differential Revision: http://reviews.llvm.org/D7216

llvm-svn: 227405

1 files changed, 106 insertions, 0 deletions

diff --git a/llvm/lib/CodeGen/WinEHPrepare.cpp b/llvm/lib/CodeGen/WinEHPrepare.cpp
new file mode 100644
index 00000000000..a01adcd43d0
--- /dev/null
+++ b/llvm/lib/CodeGen/WinEHPrepare.cpp
@@ -0,0 +1,106 @@
+//===-- WinEHPrepare - Prepare exception handling for code generation ---===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This pass lowers LLVM IR exception handling into something closer to what the
+// backend wants. It snifs the personality function to see which kind of
+// preparation is necessary. If the personality function uses the Itanium LSDA,
+// this pass delegates to the DWARF EH preparation pass.
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/CodeGen/Passes.h"
+#include "llvm/Analysis/LibCallSemantics.h"
+#include "llvm/IR/Function.h"
+#include "llvm/IR/Instructions.h"
+#include "llvm/IR/Intrinsics.h"
+#include "llvm/Pass.h"
+#include "llvm/Target/TargetLowering.h"
+using namespace llvm;
+
+#define DEBUG_TYPE "winehprepare"
+
+namespace {
+class WinEHPrepare : public FunctionPass {
+  const TargetMachine *TM;
+  FunctionPass *DwarfPrepare;
+
+public:
+  static char ID; // Pass identification, replacement for typeid.
+  WinEHPrepare(const TargetMachine *TM = nullptr)
+      : FunctionPass(ID), TM(TM), DwarfPrepare(createDwarfEHPass(TM)) {
+    initializeDominatorTreeWrapperPassPass(*PassRegistry::getPassRegistry());
+  }
+
+  bool runOnFunction(Function &Fn) override;
+
+  bool doFinalization(Module &M) override;
+
+  void getAnalysisUsage(AnalysisUsage &AU) const override;
+
+  const char *getPassName() const override {
+    return "Windows exception handling preparation";
+  }
+};
+} // end anonymous namespace
+
+char WinEHPrepare::ID = 0;
+INITIALIZE_TM_PASS(WinEHPrepare, "winehprepare",
+                   "Prepare Windows exceptions", false, false)
+
+FunctionPass *llvm::createWinEHPass(const TargetMachine *TM) {
+  return new WinEHPrepare(TM);
+}
+
+static bool isMSVCPersonality(EHPersonality Pers) {
+  return Pers == EHPersonality::MSVC_Win64SEH ||
+         Pers == EHPersonality::MSVC_CXX;
+}
+
+bool WinEHPrepare::runOnFunction(Function &Fn) {
+  SmallVector<LandingPadInst *, 4> LPads;
+  SmallVector<ResumeInst *, 4> Resumes;
+  for (BasicBlock &BB : Fn) {
+    if (auto *LP = BB.getLandingPadInst())
+      LPads.push_back(LP);
+    if (auto *Resume = dyn_cast<ResumeInst>(BB.getTerminator()))
+      Resumes.push_back(Resume);
+  }
+
+  // No need to prepare functions that lack landing pads.
+  if (LPads.empty())
+    return false;
+
+  // Classify the personality to see what kind of preparation we need.
+  EHPersonality Pers = ClassifyEHPersonality(LPads.back()->getPersonalityFn());
+
+  // Delegate through to the DWARF pass if this is unrecognized.
+  if (!isMSVCPersonality(Pers))
+    return DwarfPrepare->runOnFunction(Fn);
+
+  // FIXME: Cleanups are unimplemented. Replace them with calls to @llvm.trap.
+  if (Resumes.empty())
+    return false;
+
+  Function *Trap =
+      Intrinsic::getDeclaration(Fn.getParent(), Intrinsic::trap, None);
+  for (ResumeInst *Resume : Resumes) {
+    IRBuilder<>(Resume).CreateUnreachable();
+    Resume->eraseFromParent();
+  }
+
+  return true;
+}
+
+bool WinEHPrepare::doFinalization(Module &M) {
+  return DwarfPrepare->doFinalization(M);
+}
+
+void WinEHPrepare::getAnalysisUsage(AnalysisUsage &AU) const {
+  DwarfPrepare->getAnalysisUsage(AU);
+}