diff --git a/llvm/test/CodeGen/X86/fp-undef.ll b/llvm/test/CodeGen/X86/fp-undef.ll
new file mode 100644
index 000000000000..79e3770867b0
--- /dev/null
+++ b/llvm/test/CodeGen/X86/fp-undef.ll
@@ -0,0 +1,497 @@
+; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py
+; RUN: llc < %s -mtriple=x86_64-unknown-unknown | FileCheck %s
+
+; This is duplicated from tests for InstSimplify. If you're
+; adding something here, you should probably add it there too.
+
+define float @fadd_undef_op0(float %x) {
+; CHECK-LABEL: fadd_undef_op0:
+; CHECK:       # %bb.0:
+; CHECK-NEXT:    addss %xmm0, %xmm0
+; CHECK-NEXT:    retq
+  %r = fadd float undef, %x
+  ret float %r
+}
+
+define float @fadd_undef_op1(float %x) {
+; CHECK-LABEL: fadd_undef_op1:
+; CHECK:       # %bb.0:
+; CHECK-NEXT:    addss %xmm0, %xmm0
+; CHECK-NEXT:    retq
+  %r = fadd float %x, undef
+  ret float %r
+}
+
+define float @fsub_undef_op0(float %x) {
+; CHECK-LABEL: fsub_undef_op0:
+; CHECK:       # %bb.0:
+; CHECK-NEXT:    retq
+  %r = fsub float undef, %x
+  ret float %r
+}
+
+define float @fsub_undef_op1(float %x) {
+; CHECK-LABEL: fsub_undef_op1:
+; CHECK:       # %bb.0:
+; CHECK-NEXT:    subss %xmm0, %xmm0
+; CHECK-NEXT:    retq
+  %r = fsub float %x, undef
+  ret float %r
+}
+
+define float @fmul_undef_op0(float %x) {
+; CHECK-LABEL: fmul_undef_op0:
+; CHECK:       # %bb.0:
+; CHECK-NEXT:    mulss %xmm0, %xmm0
+; CHECK-NEXT:    retq
+  %r = fmul float undef, %x
+  ret float %r
+}
+
+define float @fmul_undef_op1(float %x) {
+; CHECK-LABEL: fmul_undef_op1:
+; CHECK:       # %bb.0:
+; CHECK-NEXT:    mulss %xmm0, %xmm0
+; CHECK-NEXT:    retq
+  %r = fmul float %x, undef
+  ret float %r
+}
+
+define float @fdiv_undef_op0(float %x) {
+; CHECK-LABEL: fdiv_undef_op0:
+; CHECK:       # %bb.0:
+; CHECK-NEXT:    retq
+  %r = fdiv float undef, %x
+  ret float %r
+}
+
+define float @fdiv_undef_op1(float %x) {
+; CHECK-LABEL: fdiv_undef_op1:
+; CHECK:       # %bb.0:
+; CHECK-NEXT:    divss %xmm0, %xmm0
+; CHECK-NEXT:    retq
+  %r = fdiv float %x, undef
+  ret float %r
+}
+
+define float @frem_undef_op0(float %x) {
+; CHECK-LABEL: frem_undef_op0:
+; CHECK:       # %bb.0:
+; CHECK-NEXT:    retq
+  %r = frem float undef, %x
+  ret float %r
+}
+
+define float @frem_undef_op1(float %x) {
+; CHECK-LABEL: frem_undef_op1:
+; CHECK:       # %bb.0:
+; CHECK-NEXT:    jmp fmodf # TAILCALL
+  %r = frem float %x, undef
+  ret float %r
+}
+
+; Repeat all tests with fast-math-flags. Alternate 'nnan' and 'fast' for more coverage.
+
+define float @fadd_undef_op0_nnan(float %x) {
+; CHECK-LABEL: fadd_undef_op0_nnan:
+; CHECK:       # %bb.0:
+; CHECK-NEXT:    addss %xmm0, %xmm0
+; CHECK-NEXT:    retq
+  %r = fadd nnan float undef, %x
+  ret float %r
+}
+
+define float @fadd_undef_op1_fast(float %x) {
+; CHECK-LABEL: fadd_undef_op1_fast:
+; CHECK:       # %bb.0:
+; CHECK-NEXT:    addss %xmm0, %xmm0
+; CHECK-NEXT:    retq
+  %r = fadd fast float %x, undef
+  ret float %r
+}
+
+define float @fsub_undef_op0_fast(float %x) {
+; CHECK-LABEL: fsub_undef_op0_fast:
+; CHECK:       # %bb.0:
+; CHECK-NEXT:    retq
+  %r = fsub fast float undef, %x
+  ret float %r
+}
+
+define float @fsub_undef_op1_nnan(float %x) {
+; CHECK-LABEL: fsub_undef_op1_nnan:
+; CHECK:       # %bb.0:
+; CHECK-NEXT:    subss %xmm0, %xmm0
+; CHECK-NEXT:    retq
+  %r = fsub nnan float %x, undef
+  ret float %r
+}
+
+define float @fmul_undef_op0_nnan(float %x) {
+; CHECK-LABEL: fmul_undef_op0_nnan:
+; CHECK:       # %bb.0:
+; CHECK-NEXT:    mulss %xmm0, %xmm0
+; CHECK-NEXT:    retq
+  %r = fmul nnan float undef, %x
+  ret float %r
+}
+
+define float @fmul_undef_op1_fast(float %x) {
+; CHECK-LABEL: fmul_undef_op1_fast:
+; CHECK:       # %bb.0:
+; CHECK-NEXT:    mulss %xmm0, %xmm0
+; CHECK-NEXT:    retq
+  %r = fmul fast float %x, undef
+  ret float %r
+}
+
+define float @fdiv_undef_op0_fast(float %x) {
+; CHECK-LABEL: fdiv_undef_op0_fast:
+; CHECK:       # %bb.0:
+; CHECK-NEXT:    retq
+  %r = fdiv fast float undef, %x
+  ret float %r
+}
+
+define float @fdiv_undef_op1_nnan(float %x) {
+; CHECK-LABEL: fdiv_undef_op1_nnan:
+; CHECK:       # %bb.0:
+; CHECK-NEXT:    divss %xmm0, %xmm0
+; CHECK-NEXT:    retq
+  %r = fdiv nnan float %x, undef
+  ret float %r
+}
+
+define float @frem_undef_op0_nnan(float %x) {
+; CHECK-LABEL: frem_undef_op0_nnan:
+; CHECK:       # %bb.0:
+; CHECK-NEXT:    retq
+  %r = frem nnan float undef, %x
+  ret float %r
+}
+
+define float @frem_undef_op1_fast(float %x) {
+; CHECK-LABEL: frem_undef_op1_fast:
+; CHECK:       # %bb.0:
+; CHECK-NEXT:    jmp fmodf # TAILCALL
+  %r = frem fast float %x, undef
+  ret float %r
+}
+
+; Constant folding - undef undef.
+
+define double @fadd_undef_undef(double %x) {
+; CHECK-LABEL: fadd_undef_undef:
+; CHECK:       # %bb.0:
+; CHECK-NEXT:    addsd %xmm0, %xmm0
+; CHECK-NEXT:    retq
+  %r = fadd double undef, undef
+  ret double %r
+}
+
+define double @fsub_undef_undef(double %x) {
+; CHECK-LABEL: fsub_undef_undef:
+; CHECK:       # %bb.0:
+; CHECK-NEXT:    retq
+  %r = fsub double undef, undef
+  ret double %r
+}
+
+define double @fmul_undef_undef(double %x) {
+; CHECK-LABEL: fmul_undef_undef:
+; CHECK:       # %bb.0:
+; CHECK-NEXT:    mulsd %xmm0, %xmm0
+; CHECK-NEXT:    retq
+  %r = fmul double undef, undef
+  ret double %r
+}
+
+define double @fdiv_undef_undef(double %x) {
+; CHECK-LABEL: fdiv_undef_undef:
+; CHECK:       # %bb.0:
+; CHECK-NEXT:    retq
+  %r = fdiv double undef, undef
+  ret double %r
+}
+
+define double @frem_undef_undef(double %x) {
+; CHECK-LABEL: frem_undef_undef:
+; CHECK:       # %bb.0:
+; CHECK-NEXT:    retq
+  %r = frem double undef, undef
+  ret double %r
+}
+
+; Constant folding.
+
+define float @fadd_undef_op0_nnan_constant(float %x) {
+; CHECK-LABEL: fadd_undef_op0_nnan_constant:
+; CHECK:       # %bb.0:
+; CHECK-NEXT:    addss {{.*}}(%rip), %xmm0
+; CHECK-NEXT:    retq
+  %r = fadd nnan float undef, 1.0
+  ret float %r
+}
+
+define float @fadd_undef_op1_constant(float %x) {
+; CHECK-LABEL: fadd_undef_op1_constant:
+; CHECK:       # %bb.0:
+; CHECK-NEXT:    addss {{.*}}(%rip), %xmm0
+; CHECK-NEXT:    retq
+  %r = fadd float 2.0, undef
+  ret float %r
+}
+
+define float @fsub_undef_op0_fast_constant(float %x) {
+; CHECK-LABEL: fsub_undef_op0_fast_constant:
+; CHECK:       # %bb.0:
+; CHECK-NEXT:    retq
+  %r = fsub fast float undef, 3.0
+  ret float %r
+}
+
+define float @fsub_undef_op1_constant(float %x) {
+; CHECK-LABEL: fsub_undef_op1_constant:
+; CHECK:       # %bb.0:
+; CHECK-NEXT:    movss {{.*#+}} xmm0 = mem[0],zero,zero,zero
+; CHECK-NEXT:    subss %xmm0, %xmm0
+; CHECK-NEXT:    retq
+  %r = fsub float 4.0, undef
+  ret float %r
+}
+
+define float @fmul_undef_op0_nnan_constant(float %x) {
+; CHECK-LABEL: fmul_undef_op0_nnan_constant:
+; CHECK:       # %bb.0:
+; CHECK-NEXT:    mulss {{.*}}(%rip), %xmm0
+; CHECK-NEXT:    retq
+  %r = fmul nnan float undef, 5.0
+  ret float %r
+}
+
+define float @fmul_undef_op1_constant(float %x) {
+; CHECK-LABEL: fmul_undef_op1_constant:
+; CHECK:       # %bb.0:
+; CHECK-NEXT:    mulss {{.*}}(%rip), %xmm0
+; CHECK-NEXT:    retq
+  %r = fmul float 6.0, undef
+  ret float %r
+}
+
+define float @fdiv_undef_op0_fast_constant(float %x) {
+; CHECK-LABEL: fdiv_undef_op0_fast_constant:
+; CHECK:       # %bb.0:
+; CHECK-NEXT:    retq
+  %r = fdiv fast float undef, 7.0
+  ret float %r
+}
+
+define float @fdiv_undef_op1_constant(float %x) {
+; CHECK-LABEL: fdiv_undef_op1_constant:
+; CHECK:       # %bb.0:
+; CHECK-NEXT:    movss {{.*#+}} xmm0 = mem[0],zero,zero,zero
+; CHECK-NEXT:    divss %xmm0, %xmm0
+; CHECK-NEXT:    retq
+  %r = fdiv float 8.0, undef
+  ret float %r
+}
+
+define float @frem_undef_op0_nnan_constant(float %x) {
+; CHECK-LABEL: frem_undef_op0_nnan_constant:
+; CHECK:       # %bb.0:
+; CHECK-NEXT:    retq
+  %r = frem nnan float undef, 9.0
+  ret float %r
+}
+
+define float @frem_undef_op1_constant(float %x) {
+; CHECK-LABEL: frem_undef_op1_constant:
+; CHECK:       # %bb.0:
+; CHECK-NEXT:    movss {{.*#+}} xmm0 = mem[0],zero,zero,zero
+; CHECK-NEXT:    jmp fmodf # TAILCALL
+  %r = frem float 10.0, undef
+  ret float %r
+}
+
+; Constant folding - special constants: NaN.
+
+define double @fadd_undef_op0_constant_nan(double %x) {
+; CHECK-LABEL: fadd_undef_op0_constant_nan:
+; CHECK:       # %bb.0:
+; CHECK-NEXT:    addsd {{.*}}(%rip), %xmm0
+; CHECK-NEXT:    retq
+  %r = fadd double undef, 0x7FF8000000000000
+  ret double %r
+}
+
+define double @fadd_undef_op1_fast_constant_nan(double %x) {
+; CHECK-LABEL: fadd_undef_op1_fast_constant_nan:
+; CHECK:       # %bb.0:
+; CHECK-NEXT:    addsd {{.*}}(%rip), %xmm0
+; CHECK-NEXT:    retq
+  %r = fadd fast double 0xFFF0000000000001, undef
+  ret double %r
+}
+
+define double @fsub_undef_op0_constant_nan(double %x) {
+; CHECK-LABEL: fsub_undef_op0_constant_nan:
+; CHECK:       # %bb.0:
+; CHECK-NEXT:    retq
+  %r = fsub double undef, 0xFFF8000000000010
+  ret double %r
+}
+
+define double @fsub_undef_op1_nnan_constant_nan(double %x) {
+; CHECK-LABEL: fsub_undef_op1_nnan_constant_nan:
+; CHECK:       # %bb.0:
+; CHECK-NEXT:    movsd {{.*#+}} xmm0 = mem[0],zero
+; CHECK-NEXT:    subsd %xmm0, %xmm0
+; CHECK-NEXT:    retq
+  %r = fsub nnan double 0x7FF0000000000011, undef
+  ret double %r
+}
+
+define double @fmul_undef_op0_constant_nan(double %x) {
+; CHECK-LABEL: fmul_undef_op0_constant_nan:
+; CHECK:       # %bb.0:
+; CHECK-NEXT:    mulsd {{.*}}(%rip), %xmm0
+; CHECK-NEXT:    retq
+  %r = fmul double undef, 0x7FF8000000000100
+  ret double %r
+}
+
+define double @fmul_undef_op1_fast_constant_nan(double %x) {
+; CHECK-LABEL: fmul_undef_op1_fast_constant_nan:
+; CHECK:       # %bb.0:
+; CHECK-NEXT:    mulsd {{.*}}(%rip), %xmm0
+; CHECK-NEXT:    retq
+  %r = fmul fast double 0xFFF0000000000101, undef
+  ret double %r
+}
+
+define double @fdiv_undef_op0_constant_nan(double %x) {
+; CHECK-LABEL: fdiv_undef_op0_constant_nan:
+; CHECK:       # %bb.0:
+; CHECK-NEXT:    retq
+  %r = fdiv double undef, 0xFFF8000000000110
+  ret double %r
+}
+
+define double @fdiv_undef_op1_nnan_constant_nan(double %x) {
+; CHECK-LABEL: fdiv_undef_op1_nnan_constant_nan:
+; CHECK:       # %bb.0:
+; CHECK-NEXT:    movsd {{.*#+}} xmm0 = mem[0],zero
+; CHECK-NEXT:    divsd %xmm0, %xmm0
+; CHECK-NEXT:    retq
+  %r = fdiv nnan double 0x7FF0000000000111, undef
+  ret double %r
+}
+
+define double @frem_undef_op0_constant_nan(double %x) {
+; CHECK-LABEL: frem_undef_op0_constant_nan:
+; CHECK:       # %bb.0:
+; CHECK-NEXT:    retq
+  %r = frem double undef, 0x7FF8000000001000
+  ret double %r
+}
+
+define double @frem_undef_op1_fast_constant_nan(double %x) {
+; CHECK-LABEL: frem_undef_op1_fast_constant_nan:
+; CHECK:       # %bb.0:
+; CHECK-NEXT:    movsd {{.*#+}} xmm0 = mem[0],zero
+; CHECK-NEXT:    jmp fmod # TAILCALL
+  %r = frem fast double 0xFFF0000000001001, undef
+  ret double %r
+}
+
+; Constant folding - special constants: Inf.
+
+define double @fadd_undef_op0_constant_inf(double %x) {
+; CHECK-LABEL: fadd_undef_op0_constant_inf:
+; CHECK:       # %bb.0:
+; CHECK-NEXT:    addsd {{.*}}(%rip), %xmm0
+; CHECK-NEXT:    retq
+  %r = fadd double undef, 0x7FF0000000000000
+  ret double %r
+}
+
+define double @fadd_undef_op1_fast_constant_inf(double %x) {
+; CHECK-LABEL: fadd_undef_op1_fast_constant_inf:
+; CHECK:       # %bb.0:
+; CHECK-NEXT:    addsd {{.*}}(%rip), %xmm0
+; CHECK-NEXT:    retq
+  %r = fadd fast double 0xFFF0000000000000, undef
+  ret double %r
+}
+
+define double @fsub_undef_op0_constant_inf(double %x) {
+; CHECK-LABEL: fsub_undef_op0_constant_inf:
+; CHECK:       # %bb.0:
+; CHECK-NEXT:    retq
+  %r = fsub double undef, 0xFFF0000000000000
+  ret double %r
+}
+
+define double @fsub_undef_op1_ninf_constant_inf(double %x) {
+; CHECK-LABEL: fsub_undef_op1_ninf_constant_inf:
+; CHECK:       # %bb.0:
+; CHECK-NEXT:    movsd {{.*#+}} xmm0 = mem[0],zero
+; CHECK-NEXT:    subsd %xmm0, %xmm0
+; CHECK-NEXT:    retq
+  %r = fsub ninf double 0x7FF0000000000000, undef
+  ret double %r
+}
+
+define double @fmul_undef_op0_constant_inf(double %x) {
+; CHECK-LABEL: fmul_undef_op0_constant_inf:
+; CHECK:       # %bb.0:
+; CHECK-NEXT:    mulsd {{.*}}(%rip), %xmm0
+; CHECK-NEXT:    retq
+  %r = fmul double undef, 0x7FF0000000000000
+  ret double %r
+}
+
+define double @fmul_undef_op1_fast_constant_inf(double %x) {
+; CHECK-LABEL: fmul_undef_op1_fast_constant_inf:
+; CHECK:       # %bb.0:
+; CHECK-NEXT:    mulsd {{.*}}(%rip), %xmm0
+; CHECK-NEXT:    retq
+  %r = fmul fast double 0xFFF0000000000000, undef
+  ret double %r
+}
+
+define double @fdiv_undef_op0_constant_inf(double %x) {
+; CHECK-LABEL: fdiv_undef_op0_constant_inf:
+; CHECK:       # %bb.0:
+; CHECK-NEXT:    retq
+  %r = fdiv double undef, 0xFFF0000000000000
+  ret double %r
+}
+
+define double @fdiv_undef_op1_ninf_constant_inf(double %x) {
+; CHECK-LABEL: fdiv_undef_op1_ninf_constant_inf:
+; CHECK:       # %bb.0:
+; CHECK-NEXT:    movsd {{.*#+}} xmm0 = mem[0],zero
+; CHECK-NEXT:    divsd %xmm0, %xmm0
+; CHECK-NEXT:    retq
+  %r = fdiv ninf double 0x7FF0000000000000, undef
+  ret double %r
+}
+
+define double @frem_undef_op0_constant_inf(double %x) {
+; CHECK-LABEL: frem_undef_op0_constant_inf:
+; CHECK:       # %bb.0:
+; CHECK-NEXT:    retq
+  %r = frem double undef, 0x7FF0000000000000
+  ret double %r
+}
+
+define double @frem_undef_op1_fast_constant_inf(double %x) {
+; CHECK-LABEL: frem_undef_op1_fast_constant_inf:
+; CHECK:       # %bb.0:
+; CHECK-NEXT:    movsd {{.*#+}} xmm0 = mem[0],zero
+; CHECK-NEXT:    jmp fmod # TAILCALL
+  %r = frem fast double 0xFFF0000000000000, undef
+  ret double %r
+}
+