1 files changed, 14 insertions, 0 deletions
diff --git a/llvm/lib/Transforms/Scalar/GVN.cpp b/llvm/lib/Transforms/Scalar/GVN.cpp
index b031f905eba..76e295c1ad2 100644
--- a/llvm/lib/Transforms/Scalar/GVN.cpp
+++ b/llvm/lib/Transforms/Scalar/GVN.cpp
@@ -2255,6 +2255,20 @@ bool GVN::performScalarPRE(Instruction *CurInst) {
   Instruction *PREInstr = nullptr;
 
   if (NumWithout != 0) {
+    if (!isSafeToSpeculativelyExecute(CurInst)) {
+      // It is only valid to insert a new instruction if the current instruction
+      // is always executed. An instruction with implicit control flow could
+      // prevent us from doing it. If we cannot speculate the execution, then
+      // PRE should be prohibited.
+      auto It = FirstImplicitControlFlowInsts.find(CurrentBlock);
+      if (It != FirstImplicitControlFlowInsts.end()) {
+        assert(It->second->getParent() == CurrentBlock &&
+               "Implicit control flow map broken?");
+        if (OI->dominates(It->second, CurInst))
+          return false;
+      }
+    }
+
     // Don't do PRE across indirect branch.
     if (isa<IndirectBrInst>(PREPred->getTerminator()))
       return false;