Index: llvm/trunk/lib/CodeGen/CodeGenPrepare.cpp
===================================================================
--- llvm/trunk/lib/CodeGen/CodeGenPrepare.cpp
+++ llvm/trunk/lib/CodeGen/CodeGenPrepare.cpp
@@ -1397,6 +1397,16 @@
       }
       return false;
     }
+    case Intrinsic::aarch64_stlxr:
+    case Intrinsic::aarch64_stxr: {
+      ZExtInst *ExtVal = dyn_cast<ZExtInst>(CI->getArgOperand(0));
+      if (!ExtVal || !ExtVal->hasOneUse() ||
+          ExtVal->getParent() == CI->getParent())
+        return false;
+      // Sink a zext feeding stlxr/stxr before it, so it can be folded into it.
+      ExtVal->moveBefore(CI);
+      return true;
+    }
     }
 
     if (TLI) {
Index: llvm/trunk/test/CodeGen/AArch64/arm64-atomic.ll
===================================================================
--- llvm/trunk/test/CodeGen/AArch64/arm64-atomic.ll
+++ llvm/trunk/test/CodeGen/AArch64/arm64-atomic.ll
@@ -2,12 +2,11 @@
 
 define i32 @val_compare_and_swap(i32* %p, i32 %cmp, i32 %new) #0 {
 ; CHECK-LABEL: val_compare_and_swap:
-; CHECK-NEXT: ubfx   x[[NEWVAL_REG:[0-9]+]], x2, #0, #32
 ; CHECK-NEXT: [[LABEL:.?LBB[0-9]+_[0-9]+]]:
 ; CHECK-NEXT: ldaxr  [[RESULT:w[0-9]+]], [x0]
 ; CHECK-NEXT: cmp    [[RESULT]], w1
 ; CHECK-NEXT: b.ne   [[LABEL2:.?LBB[0-9]+_[0-9]+]]
-; CHECK-NEXT: stxr   [[SCRATCH_REG:w[0-9]+]], w[[NEWVAL_REG]], [x0]
+; CHECK-NEXT: stxr   [[SCRATCH_REG:w[0-9]+]], w2, [x0]
 ; CHECK-NEXT: cbnz   [[SCRATCH_REG]], [[LABEL]]
 ; CHECK-NEXT: [[LABEL2]]:
   %pair = cmpxchg i32* %p, i32 %cmp, i32 %new acquire acquire
@@ -17,12 +16,11 @@
 
 define i32 @val_compare_and_swap_rel(i32* %p, i32 %cmp, i32 %new) #0 {
 ; CHECK-LABEL: val_compare_and_swap_rel:
-; CHECK-NEXT: ubfx   x[[NEWVAL_REG:[0-9]+]], x2, #0, #32
 ; CHECK-NEXT: [[LABEL:.?LBB[0-9]+_[0-9]+]]:
 ; CHECK-NEXT: ldaxr  [[RESULT:w[0-9]+]], [x0]
 ; CHECK-NEXT: cmp    [[RESULT]], w1
 ; CHECK-NEXT: b.ne   [[LABEL2:.?LBB[0-9]+_[0-9]+]]
-; CHECK-NEXT: stlxr  [[SCRATCH_REG:w[0-9]+]], w[[NEWVAL_REG]], [x0]
+; CHECK-NEXT: stlxr  [[SCRATCH_REG:w[0-9]+]], w2, [x0]
 ; CHECK-NEXT: cbnz   [[SCRATCH_REG]], [[LABEL]]
 ; CHECK-NEXT: [[LABEL2]]:
   %pair = cmpxchg i32* %p, i32 %cmp, i32 %new acq_rel monotonic