Index: llvm/lib/CodeGen/SelectionDAG/LegalizeVectorOps.cpp
===================================================================
--- llvm/lib/CodeGen/SelectionDAG/LegalizeVectorOps.cpp
+++ llvm/lib/CodeGen/SelectionDAG/LegalizeVectorOps.cpp
@@ -459,12 +459,12 @@
     break;
   }
 
-  LLVM_DEBUG(dbgs() << "\nLegalizing vector op: "; Node->dump(&DAG));
+  LLVM_DEBUG(dbgs() << "\nLegalizing vector op: "; Result->dump(&DAG));
 
   switch (Action) {
   default: llvm_unreachable("This action is not supported yet!");
   case TargetLowering::Promote:
-    Result = Promote(Op);
+    Result = Promote(Result);
     Changed = true;
     break;
   case TargetLowering::Legal:
@@ -472,7 +472,7 @@
     break;
   case TargetLowering::Custom: {
     LLVM_DEBUG(dbgs() << "Trying custom legalization\n");
-    if (SDValue Tmp1 = TLI.LowerOperation(Op, DAG)) {
+    if (SDValue Tmp1 = TLI.LowerOperation(Result, DAG)) {
       LLVM_DEBUG(dbgs() << "Successfully custom legalized node\n");
       Result = Tmp1;
       break;
@@ -481,7 +481,7 @@
     LLVM_FALLTHROUGH;
   }
   case TargetLowering::Expand:
-    Result = Expand(Op);
+    Result = Expand(Result);
   }
 
   // Make sure that the generated code is itself legal.
Index: llvm/test/CodeGen/X86/avx512-cmp.ll
===================================================================
--- llvm/test/CodeGen/X86/avx512-cmp.ll
+++ llvm/test/CodeGen/X86/avx512-cmp.ll
@@ -181,3 +181,39 @@
 if.end.i:
   ret i32 6
 }
+
+; This test previously caused an infinite loop in legalize vector ops. Due to
+; CSE triggering on the call to UpdateNodeOperands and the resulting node not
+; being passed to LowerOperation. The add is needed to force the zext into a
+; sext on that path. The shuffle keeps the zext alive. The xor somehow
+; influences the zext to be visited before the sext exposing the CSE opportunity
+; for the sext since zext of setcc is custom legalized to a sext and shift.
+define <8 x i32> @legalize_loop(<8 x double> %arg) {
+; KNL-LABEL: legalize_loop:
+; KNL:       ## %bb.0:
+; KNL-NEXT:    vxorpd %xmm1, %xmm1, %xmm1
+; KNL-NEXT:    vcmpnltpd %zmm0, %zmm1, %k1
+; KNL-NEXT:    vpternlogd $255, %zmm0, %zmm0, %zmm0 {%k1} {z}
+; KNL-NEXT:    vpsrld $31, %ymm0, %ymm1
+; KNL-NEXT:    vpshufd {{.*#+}} ymm1 = ymm1[3,2,1,0,7,6,5,4]
+; KNL-NEXT:    vpermq {{.*#+}} ymm1 = ymm1[2,3,0,1]
+; KNL-NEXT:    vpsubd %ymm0, %ymm1, %ymm0
+; KNL-NEXT:    retq
+;
+; SKX-LABEL: legalize_loop:
+; SKX:       ## %bb.0:
+; SKX-NEXT:    vxorpd %xmm1, %xmm1, %xmm1
+; SKX-NEXT:    vcmpnltpd %zmm0, %zmm1, %k0
+; SKX-NEXT:    vpmovm2d %k0, %ymm0
+; SKX-NEXT:    vpsrld $31, %ymm0, %ymm1
+; SKX-NEXT:    vpshufd {{.*#+}} ymm1 = ymm1[3,2,1,0,7,6,5,4]
+; SKX-NEXT:    vpermq {{.*#+}} ymm1 = ymm1[2,3,0,1]
+; SKX-NEXT:    vpsubd %ymm0, %ymm1, %ymm0
+; SKX-NEXT:    retq
+  %tmp = fcmp ogt <8 x double> %arg, zeroinitializer
+  %tmp1 = xor <8 x i1> %tmp, <i1 true, i1 true, i1 true, i1 true, i1 true, i1 true, i1 true, i1 true>
+  %tmp2 = zext <8 x i1> %tmp1 to <8 x i32>
+  %tmp3 = shufflevector <8 x i32> %tmp2, <8 x i32> undef, <8 x i32> <i32 7, i32 6, i32 5, i32 4, i32 3, i32 2, i32 1, i32 0>
+  %tmp4 = add <8 x i32> %tmp2, %tmp3
+  ret <8 x i32> %tmp4
+}