Index: llvm/trunk/lib/Analysis/MemorySSA.cpp
===================================================================
--- llvm/trunk/lib/Analysis/MemorySSA.cpp
+++ llvm/trunk/lib/Analysis/MemorySSA.cpp
@@ -192,8 +192,6 @@
   }
 };
 
-enum class Reorderability { Always, IfNoAlias, Never };
-
 } // end namespace llvm
 
 /// This does one-way checks to see if Use could theoretically be hoisted above
@@ -202,22 +200,16 @@
 /// This assumes that, for the purposes of MemorySSA, Use comes directly after
 /// MayClobber, with no potentially clobbering operations in between them.
 /// (Where potentially clobbering ops are memory barriers, aliased stores, etc.)
-static Reorderability getLoadReorderability(const LoadInst *Use,
-                                            const LoadInst *MayClobber) {
+static bool areLoadsReorderable(const LoadInst *Use,
+                                const LoadInst *MayClobber) {
   bool VolatileUse = Use->isVolatile();
   bool VolatileClobber = MayClobber->isVolatile();
   // Volatile operations may never be reordered with other volatile operations.
   if (VolatileUse && VolatileClobber)
-    return Reorderability::Never;
-
-  // The lang ref allows reordering of volatile and non-volatile operations.
-  // Whether an aliasing nonvolatile load and volatile load can be reordered,
-  // though, is ambiguous. Because it may not be best to exploit this ambiguity,
-  // we only allow volatile/non-volatile reordering if the volatile and
-  // non-volatile operations don't alias.
-  Reorderability Result = VolatileUse || VolatileClobber
-                              ? Reorderability::IfNoAlias
-                              : Reorderability::Always;
+    return false;
+  // Otherwise, volatile doesn't matter here. From the language reference:
+  // 'optimizers may change the order of volatile operations relative to
+  // non-volatile operations.'"
 
   // If a load is seq_cst, it cannot be moved above other loads. If its ordering
   // is weaker, it can be moved above other loads. We just need to be sure that
@@ -229,9 +221,7 @@
   bool SeqCstUse = Use->getOrdering() == AtomicOrdering::SequentiallyConsistent;
   bool MayClobberIsAcquire = isAtLeastOrStrongerThan(MayClobber->getOrdering(),
                                                      AtomicOrdering::Acquire);
-  if (SeqCstUse || MayClobberIsAcquire)
-    return Reorderability::Never;
-  return Result;
+  return !(SeqCstUse || MayClobberIsAcquire);
 }
 
 static bool instructionClobbersQuery(MemoryDef *MD,
@@ -265,18 +255,9 @@
     return isModOrRefSet(I);
   }
 
-  if (auto *DefLoad = dyn_cast<LoadInst>(DefInst)) {
-    if (auto *UseLoad = dyn_cast<LoadInst>(UseInst)) {
-      switch (getLoadReorderability(UseLoad, DefLoad)) {
-      case Reorderability::Always:
-        return false;
-      case Reorderability::Never:
-        return true;
-      case Reorderability::IfNoAlias:
-        return !AA.isNoAlias(UseLoc, MemoryLocation::get(DefLoad));
-      }
-    }
-  }
+  if (auto *DefLoad = dyn_cast<LoadInst>(DefInst))
+    if (auto *UseLoad = dyn_cast<LoadInst>(UseInst))
+      return !areLoadsReorderable(UseLoad, DefLoad);
 
   return isModSet(AA.getModRefInfo(DefInst, UseLoc));
 }
Index: llvm/trunk/test/Analysis/MemorySSA/volatile-clobber.ll
===================================================================
--- llvm/trunk/test/Analysis/MemorySSA/volatile-clobber.ll
+++ llvm/trunk/test/Analysis/MemorySSA/volatile-clobber.ll
@@ -22,8 +22,7 @@
   ret i32 %4
 }
 
-; Ensuring that we don't automatically hoist nonvolatile loads around volatile
-; loads
+; Ensuring we allow hoisting nonvolatile loads around volatile loads.
 ; CHECK-LABEL define void @volatile_only
 define void @volatile_only(i32* %arg1, i32* %arg2) {
   ; Trivially NoAlias/MustAlias
@@ -36,7 +35,7 @@
 ; CHECK: MemoryUse(liveOnEntry)
 ; CHECK-NEXT: load i32, i32* %b
   load i32, i32* %b
-; CHECK: MemoryUse(1)
+; CHECK: MemoryUse(liveOnEntry)
 ; CHECK-NEXT: load i32, i32* %a
   load i32, i32* %a
 
@@ -44,7 +43,7 @@
 ; CHECK: 2 = MemoryDef(1)
 ; CHECK-NEXT: load volatile i32, i32* %arg1
   load volatile i32, i32* %arg1
-; CHECK: MemoryUse(2)
+; CHECK: MemoryUse(liveOnEntry)
 ; CHECK-NEXT: load i32, i32* %arg2
   load i32, i32* %arg2
 
@@ -75,10 +74,10 @@
 ; CHECK: MemoryUse(1)
 ; CHECK-NEXT: load atomic i32, i32* %b unordered, align 4
   load atomic i32, i32* %b unordered, align 4
-; CHECK: MemoryUse(2)
+; CHECK: MemoryUse(1)
 ; CHECK-NEXT: load atomic i32, i32* %a unordered, align 4
   load atomic i32, i32* %a unordered, align 4
-; CHECK: MemoryUse(2)
+; CHECK: MemoryUse(1)
 ; CHECK-NEXT: load i32, i32* %a
   load i32, i32* %a
 
@@ -86,7 +85,7 @@
 ; CHECK: 3 = MemoryDef(2)
 ; CHECK-NEXT: load atomic volatile i32, i32* %arg1 monotonic, align 4
   load atomic volatile i32, i32* %arg1 monotonic, align 4
-; CHECK: MemoryUse(3)
+; CHECK: MemoryUse(1)
 ; CHECK-NEXT: load i32, i32* %arg2
   load i32, i32* %arg2