Index: llvm/trunk/include/llvm/Transforms/Scalar/Float2Int.h
===================================================================
--- llvm/trunk/include/llvm/Transforms/Scalar/Float2Int.h
+++ llvm/trunk/include/llvm/Transforms/Scalar/Float2Int.h
@@ -17,6 +17,7 @@
 #include "llvm/ADT/EquivalenceClasses.h"
 #include "llvm/ADT/MapVector.h"
 #include "llvm/IR/ConstantRange.h"
+#include "llvm/IR/Dominators.h"
 #include "llvm/IR/Function.h"
 #include "llvm/IR/PassManager.h"
 
@@ -26,10 +27,11 @@
   PreservedAnalyses run(Function &F, FunctionAnalysisManager &AM);
 
   // Glue for old PM.
-  bool runImpl(Function &F);
+  bool runImpl(Function &F, const DominatorTree &DT);
 
 private:
-  void findRoots(Function &F, SmallPtrSet<Instruction *, 8> &Roots);
+  void findRoots(Function &F, const DominatorTree &DT,
+                 SmallPtrSet<Instruction *, 8> &Roots);
   void seen(Instruction *I, ConstantRange R);
   ConstantRange badRange();
   ConstantRange unknownRange();
Index: llvm/trunk/lib/Transforms/Scalar/Float2Int.cpp
===================================================================
--- llvm/trunk/lib/Transforms/Scalar/Float2Int.cpp
+++ llvm/trunk/lib/Transforms/Scalar/Float2Int.cpp
@@ -60,11 +60,13 @@
       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 @@
 
 // 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 @@
     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 @@
 
   Ctx = &F.getParent()->getContext();
 
-  findRoots(F, Roots);
+  findRoots(F, DT, Roots);
 
   walkBackwards(Roots);
   walkForwards();
@@ -527,8 +537,9 @@
 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;
Index: llvm/trunk/test/Other/opt-O2-pipeline.ll
===================================================================
--- llvm/trunk/test/Other/opt-O2-pipeline.ll
+++ llvm/trunk/test/Other/opt-O2-pipeline.ll
@@ -185,8 +185,8 @@
 ; CHECK-NEXT:     CallGraph Construction
 ; CHECK-NEXT:     Globals Alias Analysis
 ; CHECK-NEXT:     FunctionPass Manager
-; CHECK-NEXT:       Float to int
 ; CHECK-NEXT:       Dominator Tree Construction
+; CHECK-NEXT:       Float to int
 ; CHECK-NEXT:       Basic Alias Analysis (stateless AA impl)
 ; CHECK-NEXT:       Function Alias Analysis Results
 ; CHECK-NEXT:       Memory SSA
Index: llvm/trunk/test/Other/opt-O3-pipeline.ll
===================================================================
--- llvm/trunk/test/Other/opt-O3-pipeline.ll
+++ llvm/trunk/test/Other/opt-O3-pipeline.ll
@@ -190,8 +190,8 @@
 ; CHECK-NEXT:     CallGraph Construction
 ; CHECK-NEXT:     Globals Alias Analysis
 ; CHECK-NEXT:     FunctionPass Manager
-; CHECK-NEXT:       Float to int
 ; CHECK-NEXT:       Dominator Tree Construction
+; CHECK-NEXT:       Float to int
 ; CHECK-NEXT:       Basic Alias Analysis (stateless AA impl)
 ; CHECK-NEXT:       Function Alias Analysis Results
 ; CHECK-NEXT:       Memory SSA
Index: llvm/trunk/test/Other/opt-Os-pipeline.ll
===================================================================
--- llvm/trunk/test/Other/opt-Os-pipeline.ll
+++ llvm/trunk/test/Other/opt-Os-pipeline.ll
@@ -172,8 +172,8 @@
 ; CHECK-NEXT:     CallGraph Construction
 ; CHECK-NEXT:     Globals Alias Analysis
 ; CHECK-NEXT:     FunctionPass Manager
-; CHECK-NEXT:       Float to int
 ; CHECK-NEXT:       Dominator Tree Construction
+; CHECK-NEXT:       Float to int
 ; CHECK-NEXT:       Basic Alias Analysis (stateless AA impl)
 ; CHECK-NEXT:       Function Alias Analysis Results
 ; CHECK-NEXT:       Memory SSA
Index: llvm/trunk/test/Transforms/Float2Int/basic.ll
===================================================================
--- llvm/trunk/test/Transforms/Float2Int/basic.ll
+++ llvm/trunk/test/Transforms/Float2Int/basic.ll
@@ -328,3 +328,25 @@
   %t2 = fptoui <4 x float> %t1 to <4 x i16>
   ret <4 x i16> %t2
 }
+
+; Don't crash while processing unreachable (non-standard) IR.
+
+define void @PR38502() {
+; CHECK-LABEL: @PR38502(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    ret void
+; CHECK:       bogusBB:
+; CHECK-NEXT:    [[INC1:%.*]] = fadd double [[INC:%.*]], 1.000000e+00
+; CHECK-NEXT:    [[INC]] = fadd double [[INC1]], 1.000000e+00
+; CHECK-NEXT:    [[TOBOOL:%.*]] = fcmp une double [[INC]], 0.000000e+00
+; CHECK-NEXT:    br label [[BOGUSBB:%.*]]
+;
+entry:
+  ret void
+
+bogusBB:                                          ; preds = %bogusBB
+  %inc1 = fadd double %inc, 1.000000e+00
+  %inc = fadd double %inc1, 1.000000e+00
+  %tobool = fcmp une double %inc, 0.000000e+00
+  br label %bogusBB
+}