Index: lib/Transforms/Vectorize/SLPVectorizer.cpp
===================================================================
--- lib/Transforms/Vectorize/SLPVectorizer.cpp
+++ lib/Transforms/Vectorize/SLPVectorizer.cpp
@@ -2493,10 +2493,6 @@
       Value *LHS = vectorizeTree(LHSVL);
       Value *RHS = vectorizeTree(RHSVL);
 
-      if (LHS == RHS && isa<Instruction>(LHS)) {
-        assert((VL0->getOperand(0) == VL0->getOperand(1)) && "Invalid order");
-      }
-
       if (Value *V = alreadyVectorized(E->Scalars))
         return V;
 
Index: test/Transforms/SLPVectorizer/X86/pr31599.ll
===================================================================
--- test/Transforms/SLPVectorizer/X86/pr31599.ll
+++ test/Transforms/SLPVectorizer/X86/pr31599.ll
@@ -0,0 +1,30 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
+; RUN: opt -slp-vectorizer -S -mtriple=x86_64-unknown-linux-gnu < %s | FileCheck %s
+
+define <2 x float> @foo() {
+; CHECK-LABEL: @foo(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    [[SOURCE:%.*]] = insertelement <2 x float> undef, float undef, i32 0
+; CHECK-NEXT:    [[TMP0:%.*]] = fsub <2 x float> [[SOURCE]], [[SOURCE]]
+; CHECK-NEXT:    [[TMP1:%.*]] = extractelement <2 x float> [[TMP0]], i32 0
+; CHECK-NEXT:    [[RES1:%.*]] = insertelement <2 x float> undef, float [[TMP1]], i32 0
+; CHECK-NEXT:    [[TMP2:%.*]] = extractelement <2 x float> [[TMP0]], i32 1
+; CHECK-NEXT:    [[RES2:%.*]] = insertelement <2 x float> [[RES1]], float [[TMP2]], i32 1
+; CHECK-NEXT:    ret <2 x float> [[RES2]]
+;
+entry:
+  %source = insertelement <2 x float> undef, float undef, i32 0
+  %e0 = extractelement <2 x float> %source, i32 0
+  %e0.dup = extractelement <2 x float> %source, i32 0
+  %sub1 = fsub float %e0, %e0.dup
+  %e1 = extractelement <2 x float> %source, i32 1
+  %e1.dup = extractelement <2 x float> %source, i32 1
+  %sub2 = fsub float %e1, %e1.dup
+  %res1 = insertelement <2 x float> undef, float %sub1, i32 0
+  %res2 = insertelement <2 x float> %res1, float %sub2, i32 1
+  ret <2 x float> %res2
+}
+
+!llvm.ident = !{!0, !0}
+
+!0 = !{!"clang version 4.0.0 "}