Index: llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp
===================================================================
--- llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp
+++ llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp
@@ -5629,6 +5629,11 @@
     if (LegalOperations && !isOperationLegalOrCustom(ISD::FSUB, VT))
       return NegatibleCost::Expensive;
 
+    // Ignore fadd with fneg because that will be canonicalized to fsub.
+    if (Op.getOperand(0).getOpcode() == ISD::FNEG ||
+        Op.getOperand(1).getOpcode() == ISD::FNEG)
+      return NegatibleCost::Expensive;
+
     // fold (fneg (fadd A, B)) -> (fsub (fneg A), B)
     NegatibleCost V0 = getNegatibleCost(Op.getOperand(0), DAG, LegalOperations,
                                         ForCodeSize, Depth + 1);
Index: llvm/test/CodeGen/X86/fdiv.ll
===================================================================
--- llvm/test/CodeGen/X86/fdiv.ll
+++ llvm/test/CodeGen/X86/fdiv.ll
@@ -85,11 +85,11 @@
 ; CHECK:       # %bb.0:
 ; CHECK-NEXT:    movaps %xmm0, %xmm3
 ; CHECK-NEXT:    subss %xmm1, %xmm3
+; CHECK-NEXT:    mulss %xmm2, %xmm3
 ; CHECK-NEXT:    subss %xmm0, %xmm1
-; CHECK-NEXT:    mulss %xmm2, %xmm1
-; CHECK-NEXT:    subss %xmm2, %xmm3
-; CHECK-NEXT:    divss %xmm3, %xmm1
-; CHECK-NEXT:    movaps %xmm1, %xmm0
+; CHECK-NEXT:    addss %xmm2, %xmm1
+; CHECK-NEXT:    divss %xmm1, %xmm3
+; CHECK-NEXT:    movaps %xmm3, %xmm0
 ; CHECK-NEXT:    retq
   %sub1 = fsub fast float %a0, %a1
   %mul2 = fmul fast float %sub1, %a2
Index: llvm/test/CodeGen/X86/neg_fp.ll
===================================================================
--- llvm/test/CodeGen/X86/neg_fp.ll
+++ llvm/test/CodeGen/X86/neg_fp.ll
@@ -54,3 +54,32 @@
   %t18 = fadd double %t16, %t7
   ret double %t18
 }
+
+; This would crash because the negated expression for %sub4
+; creates a new use of %sub1 and that alters the negated cost
+
+define float @fdiv_extra_use_changes_cost(float %a0, float %a1, float %a2) nounwind {
+; CHECK-LABEL: fdiv_extra_use_changes_cost:
+; CHECK:       # %bb.0:
+; CHECK-NEXT:    pushl %eax
+; CHECK-NEXT:    movss {{.*#+}} xmm0 = mem[0],zero,zero,zero
+; CHECK-NEXT:    movss {{.*#+}} xmm1 = mem[0],zero,zero,zero
+; CHECK-NEXT:    movss {{.*#+}} xmm2 = mem[0],zero,zero,zero
+; CHECK-NEXT:    movaps %xmm2, %xmm3
+; CHECK-NEXT:    subss %xmm1, %xmm3
+; CHECK-NEXT:    mulss %xmm0, %xmm3
+; CHECK-NEXT:    subss %xmm2, %xmm1
+; CHECK-NEXT:    addss %xmm0, %xmm1
+; CHECK-NEXT:    divss %xmm3, %xmm1
+; CHECK-NEXT:    movss %xmm1, (%esp)
+; CHECK-NEXT:    flds (%esp)
+; CHECK-NEXT:    popl %eax
+; CHECK-NEXT:    retl
+  %sub1 = fsub fast float %a0, %a1
+  %mul2 = fmul fast float %sub1, %a2
+  %neg = fneg fast float %a0
+  %add3 = fadd fast float %a1, %neg
+  %sub4 = fadd fast float %add3, %a2
+  %div5 = fdiv fast float %sub4, %mul2
+  ret float %div5
+}