Index: include/llvm/Transforms/Scalar/AlignmentFromAssumptions.h
===================================================================
--- include/llvm/Transforms/Scalar/AlignmentFromAssumptions.h
+++ include/llvm/Transforms/Scalar/AlignmentFromAssumptions.h
@@ -33,12 +33,6 @@
   bool runImpl(Function &F, AssumptionCache &AC, ScalarEvolution *SE_,
                DominatorTree *DT_);
 
-  // For memory transfers, we need a common alignment for both the source and
-  // destination. If we have a new alignment for only one operand of a transfer
-  // instruction, save it in these maps.  If we reach the other operand through
-  // another assumption later, then we may change the alignment at that point.
-  DenseMap<MemTransferInst *, unsigned> NewDestAlignments, NewSrcAlignments;
-
   ScalarEvolution *SE = nullptr;
   DominatorTree *DT = nullptr;
 
Index: lib/Transforms/Scalar/AlignmentFromAssumptions.cpp
===================================================================
--- lib/Transforms/Scalar/AlignmentFromAssumptions.cpp
+++ lib/Transforms/Scalar/AlignmentFromAssumptions.cpp
@@ -339,53 +339,24 @@
       unsigned NewDestAlignment = getNewAlignment(AASCEV, AlignSCEV, OffSCEV,
         MI->getDest(), SE);
 
-      // For memory transfers, we need a common alignment for both the
-      // source and destination. If we have a new alignment for this
-      // instruction, but only for one operand, save it. If we reach the
-      // other operand through another assumption later, then we may
-      // change the alignment at that point.
+      DEBUG( dbgs() << "\tmem inst: " << NewDestAlignment << "\n"; );
+      if (NewDestAlignment > MI->getDestAlignment()) {
+        MI->setDestAlignment(NewDestAlignment);
+        ++NumMemIntAlignChanged;
+      }
+      
+      // For memory transfers, there is also a source alignment that
+      // can be set.
       if (MemTransferInst *MTI = dyn_cast<MemTransferInst>(MI)) {
         unsigned NewSrcAlignment = getNewAlignment(AASCEV, AlignSCEV, OffSCEV,
           MTI->getSource(), SE);
 
-        DenseMap<MemTransferInst *, unsigned>::iterator DI =
-          NewDestAlignments.find(MTI);
-        unsigned AltDestAlignment = (DI == NewDestAlignments.end()) ?
-                                    0 : DI->second;
-
-        DenseMap<MemTransferInst *, unsigned>::iterator SI =
-          NewSrcAlignments.find(MTI);
-        unsigned AltSrcAlignment = (SI == NewSrcAlignments.end()) ?
-                                   0 : SI->second;
-
-        DEBUG(dbgs() << "\tmem trans: " << NewDestAlignment << " " <<
-                        AltDestAlignment << " " << NewSrcAlignment <<
-                        " " << AltSrcAlignment << "\n");
-
-        // Of these four alignments, pick the largest possible...
-        unsigned NewAlignment = 0;
-        if (NewDestAlignment <= std::max(NewSrcAlignment, AltSrcAlignment))
-          NewAlignment = std::max(NewAlignment, NewDestAlignment);
-        if (AltDestAlignment <= std::max(NewSrcAlignment, AltSrcAlignment))
-          NewAlignment = std::max(NewAlignment, AltDestAlignment);
-        if (NewSrcAlignment <= std::max(NewDestAlignment, AltDestAlignment))
-          NewAlignment = std::max(NewAlignment, NewSrcAlignment);
-        if (AltSrcAlignment <= std::max(NewDestAlignment, AltDestAlignment))
-          NewAlignment = std::max(NewAlignment, AltSrcAlignment);
-
-        if (NewAlignment > MI->getAlignment()) {
-          MI->setAlignment(NewAlignment);
-          ++NumMemIntAlignChanged;
-        }
-
-        NewDestAlignments.insert(std::make_pair(MTI, NewDestAlignment));
-        NewSrcAlignments.insert(std::make_pair(MTI, NewSrcAlignment));
-      } else if (NewDestAlignment > MI->getAlignment()) {
-        assert((!isa<MemIntrinsic>(MI) || isa<MemSetInst>(MI)) &&
-               "Unknown memory intrinsic");
+        DEBUG(dbgs() << "\tmem trans: " <<  NewSrcAlignment << "\n"; );
 
-        MI->setAlignment(NewDestAlignment);
-        ++NumMemIntAlignChanged;
+        if (NewSrcAlignment > MTI->getSourceAlignment()) {
+          MTI->setSourceAlignment(NewSrcAlignment);
+          ++NumMemIntAlignChanged;          
+        }
       }
     }
 
@@ -419,9 +390,6 @@
   SE = SE_;
   DT = DT_;
 
-  NewDestAlignments.clear();
-  NewSrcAlignments.clear();
-
   bool Changed = false;
   for (auto &AssumeVH : AC.assumptions())
     if (AssumeVH)
Index: test/Transforms/AlignmentFromAssumptions/simple.ll
===================================================================
--- test/Transforms/AlignmentFromAssumptions/simple.ll
+++ test/Transforms/AlignmentFromAssumptions/simple.ll
@@ -205,7 +205,7 @@
   ret i32 undef
 
 ; CHECK-LABEL: @moo2
-; CHECK: @llvm.memcpy.p0i8.p0i8.i64(i8* align 32 %0, i8* align 32 %1, i64 64, i1 false)
+; CHECK: @llvm.memcpy.p0i8.p0i8.i64(i8* align 32 %0, i8* align 128 %1, i64 64, i1 false)
 ; CHECK: ret i32 undef
 }
 
Index: test/Transforms/AlignmentFromAssumptions/simple32.ll
===================================================================
--- test/Transforms/AlignmentFromAssumptions/simple32.ll
+++ test/Transforms/AlignmentFromAssumptions/simple32.ll
@@ -205,7 +205,7 @@
   ret i32 undef
 
 ; CHECK-LABEL: @moo2
-; CHECK: @llvm.memcpy.p0i8.p0i8.i64(i8* align 32 %0, i8* align 32 %1, i64 64, i1 false)
+; CHECK: @llvm.memcpy.p0i8.p0i8.i64(i8* align 32 %0, i8* align 128 %1, i64 64, i1 false)
 ; CHECK: ret i32 undef
 }