Adding support for llvm.eh.begincatch and llvm.eh.endcatch intrinsics and beginning the documentation of native Windows exception handling.

Differential Revision: http://reviews.llvm.org/D7398



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@228733 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 192 insertions, 0 deletions

diff --git a/lib/Analysis/Lint.cpp b/lib/Analysis/Lint.cpp
index 30a26665347..beebb3b0f29 100644
--- a/lib/Analysis/Lint.cpp
+++ b/lib/Analysis/Lint.cpp
@@ -35,6 +35,7 @@
 //===----------------------------------------------------------------------===//
 
 #include "llvm/Analysis/Lint.h"
+#include "llvm/ADT/SmallSet.h"
 #include "llvm/ADT/STLExtras.h"
 #include "llvm/Analysis/AliasAnalysis.h"
 #include "llvm/Analysis/AssumptionCache.h"
@@ -73,6 +74,8 @@ namespace {
     void visitMemoryReference(Instruction &I, Value *Ptr,
                               uint64_t Size, unsigned Align,
                               Type *Ty, unsigned Flags);
+    void visitEHBeginCatch(IntrinsicInst *II);
+    void visitEHEndCatch(IntrinsicInst *II);
 
     void visitCallInst(CallInst &I);
     void visitInvokeInst(InvokeInst &I);
@@ -346,6 +349,13 @@ void Lint::visitCallSite(CallSite CS) {
       visitMemoryReference(I, CS.getArgument(0), AliasAnalysis::UnknownSize,
                            0, nullptr, MemRef::Read | MemRef::Write);
       break;
+
+    case Intrinsic::eh_begincatch:
+      visitEHBeginCatch(II);
+      break;
+    case Intrinsic::eh_endcatch:
+      visitEHEndCatch(II);
+      break;
     }
 }
 
@@ -509,6 +519,188 @@ void Lint::visitShl(BinaryOperator &I) {
             "Undefined result: Shift count out of range", &I);
 }
 
+static bool
+allPredsCameFromLandingPad(BasicBlock *BB,
+                           SmallSet<BasicBlock *, 4> &VisitedBlocks) {
+  VisitedBlocks.insert(BB);
+  if (BB->isLandingPad())
+    return true;
+  // If we find a block with no predecessors, the search failed.
+  if (pred_empty(BB))
+    return false;
+  for (BasicBlock *Pred : predecessors(BB)) {
+    if (VisitedBlocks.count(Pred))
+      continue;
+    if (!allPredsCameFromLandingPad(Pred, VisitedBlocks))
+      return false;
+  }
+  return true;
+}
+
+static bool
+allSuccessorsReachEndCatch(BasicBlock *BB, BasicBlock::iterator InstBegin,
+                           IntrinsicInst **SecondBeginCatch,
+                           SmallSet<BasicBlock *, 4> &VisitedBlocks) {
+  VisitedBlocks.insert(BB);
+  for (BasicBlock::iterator I = InstBegin, E = BB->end(); I != E; ++I) {
+    IntrinsicInst *IC = dyn_cast<IntrinsicInst>(I);
+    if (IC && IC->getIntrinsicID() == Intrinsic::eh_endcatch)
+      return true;
+    // If we find another begincatch while looking for an endcatch,
+    // that's also an error.
+    if (IC && IC->getIntrinsicID() == Intrinsic::eh_begincatch) {
+      *SecondBeginCatch = IC;
+      return false;
+    }
+  }
+
+  // If we reach a block with no successors while searching, the
+  // search has failed.
+  if (succ_empty(BB))
+    return false;
+  // Otherwise, search all of the successors.
+  for (BasicBlock *Succ : successors(BB)) {
+    if (VisitedBlocks.count(Succ))
+      continue;
+    if (!allSuccessorsReachEndCatch(Succ, Succ->begin(), SecondBeginCatch,
+                                    VisitedBlocks))
+      return false;
+  }
+  return true;
+}
+
+void Lint::visitEHBeginCatch(IntrinsicInst *II) {
+  // The checks in this function make a potentially dubious assumption about
+  // the CFG, namely that any block involved in a catch is only used for the
+  // catch.  This will very likely be true of IR generated by a front end,
+  // but it may cease to be true, for example, if the IR is run through a
+  // pass which combines similar blocks.
+  //
+  // In general, if we encounter a block the isn't dominated by the catch
+  // block while we are searching the catch block's successors for a call
+  // to end catch intrinsic, then it is possible that it will be legal for
+  // a path through this block to never reach a call to llvm.eh.endcatch.
+  // An analogous statement could be made about our search for a landing
+  // pad among the catch block's predecessors.
+  //
+  // What is actually required is that no path is possible at runtime that
+  // reaches a call to llvm.eh.begincatch without having previously visited
+  // a landingpad instruction and that no path is possible at runtime that
+  // calls llvm.eh.begincatch and does not subsequently call llvm.eh.endcatch
+  // (mentally adjusting for the fact that in reality these calls will be
+  // removed before code generation).
+  //
+  // Because this is a lint check, we take a pessimistic approach and warn if
+  // the control flow is potentially incorrect.
+
+  SmallSet<BasicBlock *, 4> VisitedBlocks;
+  BasicBlock *CatchBB = II->getParent();
+
+  // The begin catch must occur in a landing pad block or all paths
+  // to it must have come from a landing pad.
+  Assert1(allPredsCameFromLandingPad(CatchBB, VisitedBlocks),
+          "llvm.eh.begincatch may be reachable without passing a landingpad", 
+          II);
+
+  // Reset the visited block list.
+  VisitedBlocks.clear();
+
+  IntrinsicInst *SecondBeginCatch = nullptr;
+
+  // This has to be called before it is asserted.  Otherwise, the first assert
+  // below can never be hit.
+  bool EndCatchFound = allSuccessorsReachEndCatch(
+      CatchBB, std::next(static_cast<BasicBlock::iterator>(II)),
+      &SecondBeginCatch, VisitedBlocks);
+  Assert2(
+      SecondBeginCatch == nullptr,
+      "llvm.eh.begincatch may be called a second time before llvm.eh.endcatch",
+      II, SecondBeginCatch);
+  Assert1(EndCatchFound,
+          "Some paths from llvm.eh.begincatch may not reach llvm.eh.endcatch",
+          II);
+}
+
+static bool allPredCameFromBeginCatch(
+    BasicBlock *BB, BasicBlock::reverse_iterator InstRbegin,
+    IntrinsicInst **SecondEndCatch, SmallSet<BasicBlock *, 4> &VisitedBlocks) {
+  VisitedBlocks.insert(BB);
+  // Look for a begincatch in this block.
+  for (BasicBlock::reverse_iterator RI = InstRbegin, RE = BB->rend(); RI != RE;
+       ++RI) {
+    IntrinsicInst *IC = dyn_cast<IntrinsicInst>(&*RI);
+    if (IC && IC->getIntrinsicID() == Intrinsic::eh_begincatch)
+      return true;
+    // If we find another end catch before we find a begin catch, that's
+    // an error.
+    if (IC && IC->getIntrinsicID() == Intrinsic::eh_endcatch) {
+      *SecondEndCatch = IC;
+      return false;
+    }
+    // If we encounter a landingpad instruction, the search failed.
+    if (isa<LandingPadInst>(*RI))
+      return false;
+  }
+  // If while searching we find a block with no predeccesors,
+  // the search failed.
+  if (pred_empty(BB))
+    return false;
+  // Search any predecessors we haven't seen before.
+  for (BasicBlock *Pred : predecessors(BB)) {
+    if (VisitedBlocks.count(Pred))
+      continue;
+    if (!allPredCameFromBeginCatch(Pred, Pred->rbegin(), SecondEndCatch,
+                                   VisitedBlocks))
+      return false;
+  }
+  return true;
+}
+
+void Lint::visitEHEndCatch(IntrinsicInst *II) {
+  // The check in this function makes a potentially dubious assumption about
+  // the CFG, namely that any block involved in a catch is only used for the
+  // catch.  This will very likely be true of IR generated by a front end,
+  // but it may cease to be true, for example, if the IR is run through a
+  // pass which combines similar blocks.
+  //
+  // In general, if we encounter a block the isn't post-dominated by the
+  // end catch block while we are searching the end catch block's predecessors
+  // for a call to the begin catch intrinsic, then it is possible that it will
+  // be legal for a path to reach the end catch block without ever having
+  // called llvm.eh.begincatch.
+  //
+  // What is actually required is that no path is possible at runtime that
+  // reaches a call to llvm.eh.endcatch without having previously visited
+  // a call to llvm.eh.begincatch (mentally adjusting for the fact that in
+  // reality these calls will be removed before code generation).
+  //
+  // Because this is a lint check, we take a pessimistic approach and warn if
+  // the control flow is potentially incorrect.
+
+  BasicBlock *EndCatchBB = II->getParent();
+
+  // Alls paths to the end catch call must pass through a begin catch call.
+
+  // If llvm.eh.begincatch wasn't called in the current block, we'll use this
+  // lambda to recursively look for it in predecessors.
+  SmallSet<BasicBlock *, 4> VisitedBlocks;
+  IntrinsicInst *SecondEndCatch = nullptr;
+
+  // This has to be called before it is asserted.  Otherwise, the first assert
+  // below can never be hit.
+  bool BeginCatchFound =
+      allPredCameFromBeginCatch(EndCatchBB, BasicBlock::reverse_iterator(II),
+                                &SecondEndCatch, VisitedBlocks);
+  Assert2(
+      SecondEndCatch == nullptr,
+      "llvm.eh.endcatch may be called a second time after llvm.eh.begincatch",
+      II, SecondEndCatch);
+  Assert1(
+      BeginCatchFound,
+      "llvm.eh.endcatch may be reachable without passing llvm.eh.begincatch",
+      II);
+}
+
 static bool isZero(Value *V, const DataLayout *DL, DominatorTree *DT,
                    AssumptionCache *AC) {
   // Assume undef could be zero.