1 files changed, 17 insertions, 2 deletions
diff --git a/lib/Transforms/Scalar/LoadCombine.cpp b/lib/Transforms/Scalar/LoadCombine.cpp
index 389f1c595aa4..02215d3450c2 100644
--- a/lib/Transforms/Scalar/LoadCombine.cpp
+++ b/lib/Transforms/Scalar/LoadCombine.cpp
@@ -19,6 +19,7 @@
 #include "llvm/Analysis/GlobalsModRef.h"
 #include "llvm/Analysis/TargetFolder.h"
 #include "llvm/IR/DataLayout.h"
+#include "llvm/IR/Dominators.h"
 #include "llvm/IR/Function.h"
 #include "llvm/IR/IRBuilder.h"
 #include "llvm/IR/Instructions.h"
@@ -53,18 +54,20 @@ struct LoadPOPPair {
 class LoadCombine : public BasicBlockPass {
   LLVMContext *C;
   AliasAnalysis *AA;
+  DominatorTree *DT;
 
 public:
   LoadCombine() : BasicBlockPass(ID), C(nullptr), AA(nullptr) {
     initializeLoadCombinePass(*PassRegistry::getPassRegistry());
   }
-  
+
   using llvm::Pass::doInitialization;
   bool doInitialization(Function &) override;
   bool runOnBasicBlock(BasicBlock &BB) override;
   void getAnalysisUsage(AnalysisUsage &AU) const override {
     AU.setPreservesCFG();
     AU.addRequired<AAResultsWrapperPass>();
+    AU.addRequired<DominatorTreeWrapperPass>();
     AU.addPreserved<GlobalsAAWrapperPass>();
   }
 
@@ -234,6 +237,14 @@ bool LoadCombine::runOnBasicBlock(BasicBlock &BB) {
     return false;
 
   AA = &getAnalysis<AAResultsWrapperPass>().getAAResults();
+  DT = &getAnalysis<DominatorTreeWrapperPass>().getDomTree();
+
+  // Skip analysing dead blocks (not forward reachable from function entry).
+  if (!DT->isReachableFromEntry(&BB)) {
+    DEBUG(dbgs() << "LC: skipping unreachable " << BB.getName() <<
+          " in " << BB.getParent()->getName() << "\n");
+    return false;
+  }
 
   IRBuilder<TargetFolder> TheBuilder(
       BB.getContext(), TargetFolder(BB.getModule()->getDataLayout()));
@@ -245,13 +256,17 @@ bool LoadCombine::runOnBasicBlock(BasicBlock &BB) {
   bool Combined = false;
   unsigned Index = 0;
   for (auto &I : BB) {
-    if (I.mayThrow() || (I.mayWriteToMemory() && AST.containsUnknown(&I))) {
+    if (I.mayThrow() || AST.containsUnknown(&I)) {
       if (combineLoads(LoadMap))
         Combined = true;
       LoadMap.clear();
       AST.clear();
       continue;
     }
+    if (I.mayWriteToMemory()) {
+      AST.add(&I);
+      continue;
+    }
     LoadInst *LI = dyn_cast<LoadInst>(&I);
     if (!LI)
       continue;