[CodeGen] Force emission of personality directive if explicitly specified

Summary:
Before this change, personality directives were not emitted
if there was no invoke left in the function (of course until
recently this also meant that we couldn't know what
the personality actually was). This patch forces personality directives
to still be emitted, unless it is known to be a noop in the absence of
invokes, or the user explicitly specified `nounwind` (and not
`uwtable`) on the function.

Reviewers: majnemer, rnk

Subscribers: rnk, llvm-commits

Differential Revision: http://reviews.llvm.org/D10884

llvm-svn: 242185

llvm/include/llvm/Analysis/LibCallSemantics.h

@@ -206,6 +206,18 @@ class InvokeInst;
     llvm_unreachable("invalid enum");
   }
 
+  /// \brief Return true if this personality may be safely removed if there
+  /// are no invoke instructions remaining in the current function.
+  inline bool isNoOpWithoutInvoke(EHPersonality Pers) {
+    switch (Pers) {
+    case EHPersonality::Unknown:
+      return false;
+    // All known personalities currently have this behavior
+    default: return true;
+    }
+    llvm_unreachable("invalid enum");
+  }
+
   bool canSimplifyInvokeNoUnwind(const Function *F);
 
 } // end namespace llvm

llvm/include/llvm/CodeGen/MachineModuleInfo.h

@@ -320,6 +320,7 @@ public:
   /// information.
   void addPersonality(MachineBasicBlock *LandingPad,
                       const Function *Personality);
+  void addPersonality(const Function *Personality);
 
   void addWinEHState(MachineBasicBlock *LandingPad, int State);
 

llvm/lib/CodeGen/AsmPrinter/ARMException.cpp

@@ -69,24 +69,32 @@ void ARMException::beginFunction(const MachineFunction *MF) {
 ///
 void ARMException::endFunction(const MachineFunction *MF) {
   ARMTargetStreamer &ATS = getTargetStreamer();
+  const Function *F = MF->getFunction();
+  const Function *Per = nullptr;
+  if (F->hasPersonalityFn())
+    Per = dyn_cast<Function>(F->getPersonalityFn()->stripPointerCasts());
+  assert(!MMI->getPersonality() || Per == MMI->getPersonality());
+  bool forceEmitPersonality =
+    F->hasPersonalityFn() && !isNoOpWithoutInvoke(classifyEHPersonality(Per)) &&
+    F->needsUnwindTableEntry();
+  bool shouldEmitPersonality = forceEmitPersonality ||
+    !MMI->getLandingPads().empty();
   if (!Asm->MF->getFunction()->needsUnwindTableEntry() &&
-      MMI->getLandingPads().empty())
+      !shouldEmitPersonality)
     ATS.emitCantUnwind();
-  else {
-    if (!MMI->getLandingPads().empty()) {
-      // Emit references to personality.
-      if (const Function *Personality = MMI->getPersonality()) {
-        MCSymbol *PerSym = Asm->getSymbol(Personality);
-        Asm->OutStreamer->EmitSymbolAttribute(PerSym, MCSA_Global);
-        ATS.emitPersonality(PerSym);
-      }
-
-      // Emit .handlerdata directive.
-      ATS.emitHandlerData();
-
-      // Emit actual exception table
-      emitExceptionTable();
+  else if (shouldEmitPersonality) {
+    // Emit references to personality.
+    if (Per) {
+      MCSymbol *PerSym = Asm->getSymbol(Per);
+      Asm->OutStreamer->EmitSymbolAttribute(PerSym, MCSA_Global);
+      ATS.emitPersonality(PerSym);
     }
+
+    // Emit .handlerdata directive.
+    ATS.emitHandlerData();
+
+    // Emit actual exception table
+    emitExceptionTable();
   }
 
   if (Asm->MAI->getExceptionHandlingType() == ExceptionHandling::ARM)

llvm/lib/CodeGen/AsmPrinter/DwarfCFIException.cpp

@@ -89,6 +89,7 @@ void DwarfCFIException::endModule() {
 
 void DwarfCFIException::beginFunction(const MachineFunction *MF) {
   shouldEmitMoves = shouldEmitPersonality = shouldEmitLSDA = false;
+  const Function *F = MF->getFunction();
 
   // If any landing pads survive, we need an EH table.
   bool hasLandingPads = !MMI->getLandingPads().empty();
@@ -104,10 +105,24 @@ void DwarfCFIException::beginFunction(const MachineFunction *MF) {
 
   const TargetLoweringObjectFile &TLOF = Asm->getObjFileLowering();
   unsigned PerEncoding = TLOF.getPersonalityEncoding();
-  const Function *Per = MMI->getPersonality();
+  const Function *Per = nullptr;
+  if (F->hasPersonalityFn())
+    Per = dyn_cast<Function>(F->getPersonalityFn()->stripPointerCasts());
+  assert(!MMI->getPersonality() || Per == MMI->getPersonality());
 
-  shouldEmitPersonality = hasLandingPads &&
-    PerEncoding != dwarf::DW_EH_PE_omit && Per;
+  // Emit a personality function even when there are no landing pads
+  bool forceEmitPersonality =
+      // ...if a personality function is explicitly specified
+      F->hasPersonalityFn() &&
+      // ... and it's not known to be a noop in the absence of invokes
+      !isNoOpWithoutInvoke(classifyEHPersonality(Per)) &&
+      // ... and we're not explicitly asked not to emit it
+      F->needsUnwindTableEntry();
+
+  shouldEmitPersonality =
+      (forceEmitPersonality ||
+       (hasLandingPads && PerEncoding != dwarf::DW_EH_PE_omit)) &&
+      Per;
 
   unsigned LSDAEncoding = TLOF.getLSDAEncoding();
   shouldEmitLSDA = shouldEmitPersonality &&
@@ -123,6 +138,11 @@ void DwarfCFIException::beginFunction(const MachineFunction *MF) {
   if (!shouldEmitPersonality)
     return;
 
+  // If we are forced to emit this personality, make sure to record
+  // it because it might not appear in any landingpad
+  if (forceEmitPersonality)
+    MMI->addPersonality(Per);
+
   const MCSymbol *Sym =
       TLOF.getCFIPersonalitySymbol(Per, *Asm->Mang, Asm->TM, MMI);
   Asm->OutStreamer->EmitCFIPersonality(Sym, PerEncoding);

llvm/lib/CodeGen/AsmPrinter/EHStreamer.cpp

@@ -309,7 +309,7 @@ computeCallSiteTable(SmallVectorImpl<CallSiteEntry> &CallSites,
   // If some instruction between the previous try-range and the end of the
   // function may throw, create a call-site entry with no landing pad for the
   // region following the try-range.
-  if (SawPotentiallyThrowing && !IsSJLJ) {
+  if (SawPotentiallyThrowing && !IsSJLJ && LastLabel != nullptr) {
     CallSiteEntry Site = { LastLabel, nullptr, nullptr, 0 };
     CallSites.push_back(Site);
   }

llvm/lib/CodeGen/AsmPrinter/WinException.cpp

@@ -74,8 +74,12 @@ void WinException::beginFunction(const MachineFunction *MF) {
   if (F->hasPersonalityFn())
     Per = dyn_cast<Function>(F->getPersonalityFn()->stripPointerCasts());
 
-  shouldEmitPersonality = hasLandingPads &&
-    PerEncoding != dwarf::DW_EH_PE_omit && Per;
+  bool forceEmitPersonality =
+    F->hasPersonalityFn() && !isNoOpWithoutInvoke(classifyEHPersonality(Per)) &&
+    F->needsUnwindTableEntry();
+
+  shouldEmitPersonality = forceEmitPersonality || (hasLandingPads &&
+    PerEncoding != dwarf::DW_EH_PE_omit && Per);
 
   unsigned LSDAEncoding = TLOF.getLSDAEncoding();
   shouldEmitLSDA = shouldEmitPersonality &&

llvm/lib/CodeGen/MachineModuleInfo.cpp

@@ -320,7 +320,10 @@ void MachineModuleInfo::addPersonality(MachineBasicBlock *LandingPad,
                                        const Function *Personality) {
   LandingPadInfo &LP = getOrCreateLandingPadInfo(LandingPad);
   LP.Personality = Personality;
+  addPersonality(Personality);
+}
 
+void MachineModuleInfo::addPersonality(const Function *Personality) {
   for (unsigned i = 0; i < Personalities.size(); ++i)
     if (Personalities[i] == Personality)
       return;

llvm/test/CodeGen/X86/eh-nolandingpads.ll

@@ -0,0 +1,12 @@
+; RUN: llc < %s -mtriple=x86_64-pc-linux | FileCheck %s
+; Test that we emit functions with explicitly specified personality,
+; even if no landing pads are left.
+
+declare i32 @__my_personality_v0(...)
+declare void @might_throw()
+
+define i32 @foo() personality i32 (...)* @__my_personality_v0 {
+; CHECK: .cfi_personality 3, __my_personality_v0
+    call void @might_throw()
+    ret i32 0
+}