Index: llvm/lib/CodeGen/CriticalAntiDepBreaker.cpp
===================================================================
--- llvm/lib/CodeGen/CriticalAntiDepBreaker.cpp
+++ llvm/lib/CodeGen/CriticalAntiDepBreaker.cpp
@@ -261,15 +261,28 @@
     for (unsigned i = 0, e = MI.getNumOperands(); i != e; ++i) {
       MachineOperand &MO = MI.getOperand(i);
 
-      if (MO.isRegMask())
-        for (unsigned i = 0, e = TRI->getNumRegs(); i != e; ++i)
+      if (MO.isRegMask()) {
+        for (unsigned i = 0, e = TRI->getNumRegs(); i != e; ++i) {
           if (MO.clobbersPhysReg(i)) {
-            DefIndices[i] = Count;
-            KillIndices[i] = ~0u;
-            KeepRegs.reset(i);
-            Classes[i] = nullptr;
-            RegRefs.erase(i);
+            // Make sure all subregisters are also clobbered.
+            bool PreservesSubReg = false;
+            for (MCSubRegIterator SRI(i, TRI, true); SRI.isValid(); ++SRI) {
+              if (!MO.clobbersPhysReg(*SRI)) {
+                PreservesSubReg = true;
+                break;
+              }
+            }
+
+            if (!PreservesSubReg) {
+              DefIndices[i] = Count;
+              KillIndices[i] = ~0u;
+              KeepRegs.reset(i);
+              Classes[i] = nullptr;
+              RegRefs.erase(i);
+            }
           }
+        }
+      }
 
       if (!MO.isReg()) continue;
       Register Reg = MO.getReg();
Index: llvm/test/CodeGen/X86/pr44140.ll
===================================================================
--- llvm/test/CodeGen/X86/pr44140.ll
+++ llvm/test/CodeGen/X86/pr44140.ll
@@ -23,7 +23,7 @@
 ; CHECK-NEXT:    # =>This Inner Loop Header: Depth=1
 ; CHECK-NEXT:    vmovups {{[0-9]+}}(%rsp), %ymm0
 ; CHECK-NEXT:    vmovups {{[0-9]+}}(%rsp), %ymm1
-; CHECK-NEXT:    vmovups {{[0-9]+}}(%rsp), %ymm6
+; CHECK-NEXT:    vmovups {{[0-9]+}}(%rsp), %ymm7
 ; CHECK-NEXT:    vmovups {{[0-9]+}}(%rsp), %ymm2
 ; CHECK-NEXT:    vmovups {{[0-9]+}}(%rsp), %ymm3
 ; CHECK-NEXT:    vmovups %ymm0, {{[0-9]+}}(%rsp)
@@ -31,10 +31,10 @@
 ; CHECK-NEXT:    vmovups {{[0-9]+}}(%rsp), %ymm1
 ; CHECK-NEXT:    vmovups %ymm3, {{[0-9]+}}(%rsp)
 ; CHECK-NEXT:    vmovups %ymm2, {{[0-9]+}}(%rsp)
-; CHECK-NEXT:    vmovups %ymm6, {{[0-9]+}}(%rsp)
+; CHECK-NEXT:    vmovups %ymm7, {{[0-9]+}}(%rsp)
 ; CHECK-NEXT:    vmovups %ymm3, {{[0-9]+}}(%rsp)
 ; CHECK-NEXT:    vmovups %ymm2, {{[0-9]+}}(%rsp)
-; CHECK-NEXT:    vmovups %ymm6, {{[0-9]+}}(%rsp)
+; CHECK-NEXT:    vmovups %ymm7, {{[0-9]+}}(%rsp)
 ; CHECK-NEXT:    vmovups %ymm1, {{[0-9]+}}(%rsp)
 ; CHECK-NEXT:    vmovups %ymm1, {{[0-9]+}}(%rsp)
 ; CHECK-NEXT:    vmovups {{[0-9]+}}(%rsp), %ymm5