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

llvm/include/llvm/CodeGen/Passes.h

@@ -573,6 +573,10 @@ namespace llvm {
   /// adapted to code generation.  Required if using dwarf exception handling.
   FunctionPass *createDwarfEHPass(const TargetMachine *TM);
 
+  /// createWinEHPass - Prepares personality functions used by MSVC on Windows,
+  /// in addition to the Itanium LSDA based personalities.
+  FunctionPass *createWinEHPass(const TargetMachine *TM);
+
   /// createSjLjEHPreparePass - This pass adapts exception handling code to use
   /// the GCC-style builtin setjmp/longjmp (sjlj) to handling EH control flow.
   ///

llvm/include/llvm/InitializePasses.h

@@ -289,6 +289,7 @@ void initializeStackMapLivenessPass(PassRegistry&);
 void initializeMachineCombinerPass(PassRegistry &);
 void initializeLoadCombinePass(PassRegistry&);
 void initializeRewriteSymbolsPass(PassRegistry&);
+void initializeWinEHPreparePass(PassRegistry&);
 }
 
 #endif

llvm/lib/CodeGen/CMakeLists.txt

@@ -118,6 +118,7 @@ add_llvm_library(LLVMCodeGen
   TwoAddressInstructionPass.cpp
   UnreachableBlockElim.cpp
   VirtRegMap.cpp
+  WinEHPrepare.cpp
   )
 
 add_dependencies(LLVMCodeGen intrinsics_gen)

llvm/lib/CodeGen/Passes.cpp

@@ -450,9 +450,11 @@ void TargetPassConfig::addPassesToHandleExceptions() {
     // FALLTHROUGH
   case ExceptionHandling::DwarfCFI:
   case ExceptionHandling::ARM:
-  case ExceptionHandling::WinEH:
     addPass(createDwarfEHPass(TM));
     break;
+  case ExceptionHandling::WinEH:
+    addPass(createWinEHPass(TM));
+    break;
   case ExceptionHandling::None:
     addPass(createLowerInvokePass());
 

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);
+}

llvm/test/CodeGen/X86/seh-safe-div.ll

@@ -96,8 +96,9 @@ __try.cont:
 ; CHECK: movl $-2, [[rloc]]
 ; CHECK: jmp .LBB0_7
 
-; FIXME: EH preparation should not call _Unwind_Resume.
-; CHECK: callq _Unwind_Resume
+; FIXME: EH preparation should eliminate the 'resume' instr and we should not do
+; the previous 'cmp;jeq'.
+; CHECK-NOT: _Unwind_Resume
 ; CHECK: ud2
 
 ; CHECK: .seh_handlerdata

llvm/test/CodeGen/X86/win_eh_prepare.ll

@@ -0,0 +1,80 @@
+; RUN: opt -S -winehprepare -mtriple x86_64-pc-windows-msvc < %s | FileCheck %s
+
+; FIXME: Add and test outlining here.
+
+declare void @maybe_throw()
+
+@_ZTIi = external constant i8*
+@g = external global i32
+
+declare i32 @__C_specific_handler(...)
+declare i32 @__gxx_personality_seh0(...)
+declare i32 @llvm.eh.typeid.for(i8*) readnone nounwind
+
+define i32 @use_seh() {
+entry:
+  invoke void @maybe_throw()
+      to label %cont unwind label %lpad
+
+cont:
+  ret i32 0
+
+lpad:
+  %ehvals = landingpad { i8*, i32 } personality i32 (...)* @__C_specific_handler
+      cleanup
+      catch i8* bitcast (i32 (i8*, i8*)* @filt_g to i8*)
+  %ehsel = extractvalue { i8*, i32 } %ehvals, 1
+  %filt_g_sel = call i32 @llvm.eh.typeid.for(i8* bitcast (i32 (i8*, i8*)* @filt_g to i8*))
+  %matches = icmp eq i32 %ehsel, %filt_g_sel
+  br i1 %matches, label %ret1, label %eh.resume
+
+ret1:
+  ret i32 1
+
+eh.resume:
+  resume { i8*, i32 } %ehvals
+}
+
+define internal i32 @filt_g(i8*, i8*) {
+  %g = load i32* @g
+  ret i32 %g
+}
+
+; CHECK-LABEL: define i32 @use_seh()
+; CHECK: invoke void @maybe_throw()
+; CHECK-NEXT: to label %cont unwind label %lpad
+; CHECK: eh.resume:
+; CHECK-NEXT: unreachable
+
+
+; A MinGW64-ish EH style. It could happen if a binary uses both MSVC CRT and
+; mingw CRT and is linked with LTO.
+define i32 @use_gcc() {
+entry:
+  invoke void @maybe_throw()
+      to label %cont unwind label %lpad
+
+cont:
+  ret i32 0
+
+lpad:
+  %ehvals = landingpad { i8*, i32 } personality i32 (...)* @__gxx_personality_seh0
+      cleanup
+      catch i8* bitcast (i8** @_ZTIi to i8*)
+  %ehsel = extractvalue { i8*, i32 } %ehvals, 1
+  %filt_g_sel = call i32 @llvm.eh.typeid.for(i8* bitcast (i32 (i8*, i8*)* @filt_g to i8*))
+  %matches = icmp eq i32 %ehsel, %filt_g_sel
+  br i1 %matches, label %ret1, label %eh.resume
+
+ret1:
+  ret i32 1
+
+eh.resume:
+  resume { i8*, i32 } %ehvals
+}
+
+; CHECK-LABEL: define i32 @use_gcc()
+; CHECK: invoke void @maybe_throw()
+; CHECK-NEXT: to label %cont unwind label %lpad
+; CHECK: eh.resume:
+; CHECK: call void @_Unwind_Resume(i8* %exn.obj)

llvm/tools/opt/opt.cpp

@@ -322,6 +322,7 @@ int main(int argc, char **argv) {
   initializeCodeGenPreparePass(Registry);
   initializeAtomicExpandPass(Registry);
   initializeRewriteSymbolsPass(Registry);
+  initializeWinEHPreparePass(Registry);
 
 #ifdef LINK_POLLY_INTO_TOOLS
   polly::initializePollyPasses(Registry);