[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

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@242185 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/include/llvm/Analysis/LibCallSemantics.h b/include/llvm/Analysis/LibCallSemantics.h
index 170e2a4..b4bef31 100644 (file)
--- a/include/llvm/Analysis/LibCallSemantics.h
+++ b/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

diff --git a/include/llvm/CodeGen/MachineModuleInfo.h b/include/llvm/CodeGen/MachineModuleInfo.h
index ccaa83a..4cdfe24 100644 (file)
--- a/include/llvm/CodeGen/MachineModuleInfo.h
+++ b/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);
 

diff --git a/lib/CodeGen/AsmPrinter/ARMException.cpp b/lib/CodeGen/AsmPrinter/ARMException.cpp
index 4cb460a..0bad795 100644 (file)
--- a/lib/CodeGen/AsmPrinter/ARMException.cpp
+++ b/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)

diff --git a/lib/CodeGen/AsmPrinter/DwarfCFIException.cpp b/lib/CodeGen/AsmPrinter/DwarfCFIException.cpp
index 0bc873e..2c212c7 100644 (file)
--- a/lib/CodeGen/AsmPrinter/DwarfCFIException.cpp
+++ b/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();
-
-  shouldEmitPersonality = hasLandingPads &&
-    PerEncoding != dwarf::DW_EH_PE_omit && Per;
+  const Function *Per = nullptr;
+  if (F->hasPersonalityFn())
+    Per = dyn_cast<Function>(F->getPersonalityFn()->stripPointerCasts());
+  assert(!MMI->getPersonality() || Per == MMI->getPersonality());
+
+  // 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);

diff --git a/lib/CodeGen/AsmPrinter/EHStreamer.cpp b/lib/CodeGen/AsmPrinter/EHStreamer.cpp
index 1be3fd7..49ef8d3 100644 (file)
--- a/lib/CodeGen/AsmPrinter/EHStreamer.cpp
+++ b/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);
   }

diff --git a/lib/CodeGen/AsmPrinter/WinException.cpp b/lib/CodeGen/AsmPrinter/WinException.cpp
index 7ef2832..71c7781 100644 (file)
--- a/lib/CodeGen/AsmPrinter/WinException.cpp
+++ b/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 &&

diff --git a/lib/CodeGen/MachineModuleInfo.cpp b/lib/CodeGen/MachineModuleInfo.cpp
index 42d0603..6a20624 100644 (file)
--- a/lib/CodeGen/MachineModuleInfo.cpp
+++ b/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;

diff --git a/test/CodeGen/X86/eh-nolandingpads.ll b/test/CodeGen/X86/eh-nolandingpads.ll
new file mode 100644 (file)
index 0000000..9629522
--- /dev/null
+++ b/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
+}