[Float2Int] avoid crashing on unreachable code (PR38502)

In the example from:
https://bugs.llvm.org/show_bug.cgi?id=38502
...we hit infinite looping/crashing because we have non-standard IR -
an instruction operand is used before defined.
This and other unusual constructs are allowed in unreachable blocks,
so avoid the problem by using DominatorTree to step around landmines.

Differential Revision: https://reviews.llvm.org/D67766

llvm-svn: 372339

1 files changed, 29 insertions, 18 deletions

diff --git a/llvm/lib/Transforms/Scalar/Float2Int.cpp b/llvm/lib/Transforms/Scalar/Float2Int.cpp
index 4f83e869b30..4d2eac0451d 100644
--- a/llvm/lib/Transforms/Scalar/Float2Int.cpp
+++ b/llvm/lib/Transforms/Scalar/Float2Int.cpp
@@ -60,11 +60,13 @@ namespace {
       if (skipFunction(F))
         return false;
 
-      return Impl.runImpl(F);
+      const DominatorTree &DT = getAnalysis<DominatorTreeWrapperPass>().getDomTree();
+      return Impl.runImpl(F, DT);
     }
 
     void getAnalysisUsage(AnalysisUsage &AU) const override {
       AU.setPreservesCFG();
+      AU.addRequired<DominatorTreeWrapperPass>();
       AU.addPreserved<GlobalsAAWrapperPass>();
     }
 
@@ -116,21 +118,29 @@ static Instruction::BinaryOps mapBinOpcode(unsigned Opcode) {
 
 // Find the roots - instructions that convert from the FP domain to
 // integer domain.
-void Float2IntPass::findRoots(Function &F, SmallPtrSet<Instruction*,8> &Roots) {
-  for (auto &I : instructions(F)) {
-    if (isa<VectorType>(I.getType()))
+void Float2IntPass::findRoots(Function &F, const DominatorTree &DT,
+                              SmallPtrSet<Instruction*,8> &Roots) {
+  for (BasicBlock &BB : F) {
+    // Unreachable code can take on strange forms that we are not prepared to
+    // handle. For example, an instruction may have itself as an operand.
+    if (!DT.isReachableFromEntry(&BB))
       continue;
-    switch (I.getOpcode()) {
-    default: break;
-    case Instruction::FPToUI:
-    case Instruction::FPToSI:
-      Roots.insert(&I);
-      break;
-    case Instruction::FCmp:
-      if (mapFCmpPred(cast<CmpInst>(&I)->getPredicate()) !=
-          CmpInst::BAD_ICMP_PREDICATE)
+
+    for (Instruction &I : BB) {
+      if (isa<VectorType>(I.getType()))
+        continue;
+      switch (I.getOpcode()) {
+      default: break;
+      case Instruction::FPToUI:
+      case Instruction::FPToSI:
         Roots.insert(&I);
-      break;
+        break;
+      case Instruction::FCmp:
+        if (mapFCmpPred(cast<CmpInst>(&I)->getPredicate()) !=
+            CmpInst::BAD_ICMP_PREDICATE)
+          Roots.insert(&I);
+        break;
+      }
     }
   }
 }
@@ -503,7 +513,7 @@ void Float2IntPass::cleanup() {
     I.first->eraseFromParent();
 }
 
-bool Float2IntPass::runImpl(Function &F) {
+bool Float2IntPass::runImpl(Function &F, const DominatorTree &DT) {
   LLVM_DEBUG(dbgs() << "F2I: Looking at function " << F.getName() << "\n");
   // Clear out all state.
   ECs = EquivalenceClasses<Instruction*>();
@@ -513,7 +523,7 @@ bool Float2IntPass::runImpl(Function &F) {
 
   Ctx = &F.getParent()->getContext();
 
-  findRoots(F, Roots);
+  findRoots(F, DT, Roots);
 
   walkBackwards(Roots);
   walkForwards();
@@ -527,8 +537,9 @@ bool Float2IntPass::runImpl(Function &F) {
 namespace llvm {
 FunctionPass *createFloat2IntPass() { return new Float2IntLegacyPass(); }
 
-PreservedAnalyses Float2IntPass::run(Function &F, FunctionAnalysisManager &) {
-  if (!runImpl(F))
+PreservedAnalyses Float2IntPass::run(Function &F, FunctionAnalysisManager &AM) {
+  const DominatorTree &DT = AM.getResult<DominatorTreeAnalysis>(F);
+  if (!runImpl(F, DT))
     return PreservedAnalyses::all();
 
   PreservedAnalyses PA;