Index: lib/Analysis/MemoryDependenceAnalysis.cpp
===================================================================
--- lib/Analysis/MemoryDependenceAnalysis.cpp
+++ lib/Analysis/MemoryDependenceAnalysis.cpp
@@ -494,6 +494,14 @@
 
   const DataLayout &DL = BB->getModule()->getDataLayout();
 
+  // We're about to scan backwards. Preserve the initial invariant_start
+  // intrinsic marking on this load, for subsequent instructions.
+  // First, compute the info to preserve.
+  // Then, actually preserve the info before backward scanning starts.
+  InvariantInfo &InvInfo = BB->getModule()->getInvariantInfo();
+  PreservedInvariantInfo Preserved(isLoad ? QueryInst : nullptr, DL, InvInfo);
+  PreserveInvariantInfo PIO(Preserved);
+
   // Create a numbered basic block to lazily compute and cache instruction
   // positions inside a BB. This is used to provide fast queries for relative
   // position between two instructions in a BB and can be used by
@@ -504,10 +512,15 @@
   while (ScanIt != BB->begin()) {
     Instruction *Inst = --ScanIt;
 
-    if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(Inst))
+    if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(Inst)) {
       // Debug intrinsics don't (and can't) cause dependencies.
       if (isa<DbgInfoIntrinsic>(II)) continue;
 
+      // Same for invariant intrinsics, which may also unset preserved
+      // invariant info.
+      if (BackwardScanInvariantIntrinsic(II, Preserved, InvInfo)) continue;
+    }
+
     // Limit the amount of scanning we do so we don't end up with quadratic
     // running time on extreme testcases.
     --Limit;
Index: lib/Transforms/Scalar/GVN.cpp
===================================================================
--- lib/Transforms/Scalar/GVN.cpp
+++ lib/Transforms/Scalar/GVN.cpp
@@ -2282,6 +2282,13 @@
   if (isa<DbgInfoIntrinsic>(I))
     return false;
 
+
+  // Also ignore invariant intrinsics, after processing them.
+  if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(I)) {
+    InvariantInfo &InvInfo = I->getModule()->getInvariantInfo();
+    if (processInvariantIntrinsic(II, InvInfo)) return false;
+  }
+
   // If the instruction can be easily simplified then do so now in preference
   // to value numbering it.  Value numbering often exposes redundancies, for
   // example if it determines that %y is equal to %x then the instruction