diff --git a/SwiftCompilerSources/Sources/Optimizer/InstructionSimplification/SimplifyBuiltin.swift b/SwiftCompilerSources/Sources/Optimizer/InstructionSimplification/SimplifyBuiltin.swift
index 0af3cc3d9ab02..c1ec891ad1e05 100644
--- a/SwiftCompilerSources/Sources/Optimizer/InstructionSimplification/SimplifyBuiltin.swift
+++ b/SwiftCompilerSources/Sources/Optimizer/InstructionSimplification/SimplifyBuiltin.swift
@@ -53,6 +53,8 @@ extension BuiltinInst : OnoneSimplifiable {
         constantFoldIntegerEquality(isEqual: true, context)
       case .ICMP_NE:
         constantFoldIntegerEquality(isEqual: false, context)
+      case .Xor:
+        simplifyNegation(context)
       default:
         if let literal = constantFold(context) {
           uses.replaceAll(with: literal, context)
@@ -224,6 +226,53 @@ private extension BuiltinInst {
     }
     return false
   }
+
+  /// Replaces a builtin "xor", which negates its operand comparison
+  /// ```
+  ///   %3 = builtin "cmp_slt_Int64"(%1, %2) : $Builtin.Int1
+  ///   %4 = integer_literal $Builtin.Int1, -1
+  ///   %5 = builtin "xor_Int1"(%3, %4) : $Builtin.Int1
+  /// ```
+  /// with the negated comparison
+  /// ```
+  ///   %5 = builtin "cmp_ge_Int64"(%1, %2) : $Builtin.Int1
+  /// ```
+  func simplifyNegation(_ context: SimplifyContext) {
+    assert(id == .Xor)
+    guard let one = arguments[1] as? IntegerLiteralInst,
+          let oneValue = one.value,
+          oneValue == -1,
+          let lhsBuiltin = arguments[0] as? BuiltinInst,
+          lhsBuiltin.type.isBuiltinInteger,
+          let negatedBuiltinName = lhsBuiltin.negatedComparisonBuiltinName
+    else {
+      return
+    }
+
+    let builder = Builder(before: lhsBuiltin, context)
+    let negated = builder.createBuiltinBinaryFunction(name: negatedBuiltinName,
+        operandType: lhsBuiltin.arguments[0].type,
+        resultType: lhsBuiltin.type,
+        arguments: Array(lhsBuiltin.arguments))
+    self.replace(with: negated, context)
+  }
+
+  private var negatedComparisonBuiltinName: String? {
+    switch id {
+    case .ICMP_EQ:  return "cmp_ne"
+    case .ICMP_NE:  return "cmp_eq"
+    case .ICMP_SLE: return "cmp_sgt"
+    case .ICMP_SLT: return "cmp_sge"
+    case .ICMP_SGE: return "cmp_slt"
+    case .ICMP_SGT: return "cmp_sle"
+    case .ICMP_ULE: return "cmp_ugt"
+    case .ICMP_ULT: return "cmp_uge"
+    case .ICMP_UGE: return "cmp_ult"
+    case .ICMP_UGT: return "cmp_ule"
+    default:
+      return nil
+    }
+  }
 }
 
 private extension Value {
diff --git a/test/SILOptimizer/simplify_builtin.sil b/test/SILOptimizer/simplify_builtin.sil
index c14f349629cef..5aa7398f302b6 100644
--- a/test/SILOptimizer/simplify_builtin.sil
+++ b/test/SILOptimizer/simplify_builtin.sil
@@ -694,3 +694,166 @@ bb0:
   return %0
 }
 
+// CHECK-LABEL: sil @invert_comparison_eq :
+// CHECK:         %2 = builtin "cmp_ne_Int64"(%0 : $Builtin.Int64, %1 : $Builtin.Int64)
+// CHECK:         return %2
+// CHECK:       } // end sil function 'invert_comparison_eq'
+sil @invert_comparison_eq : $@convention(thin) (Builtin.Int64, Builtin.Int64) -> Builtin.Int1 {
+bb0(%0 : $Builtin.Int64, %1 : $Builtin.Int64):
+  %2 = builtin "cmp_eq_Int64"(%0, %1) : $Builtin.Int1
+  %3 = integer_literal $Builtin.Int1, -1
+  %4 = builtin "xor_Int1"(%2, %3) : $Builtin.Int1
+  return %4
+}
+
+// CHECK-LABEL: sil @invert_comparison_ne :
+// CHECK:         %2 = builtin "cmp_eq_Int64"(%0 : $Builtin.Int64, %1 : $Builtin.Int64)
+// CHECK:         return %2
+// CHECK:       } // end sil function 'invert_comparison_ne'
+sil @invert_comparison_ne : $@convention(thin) (Builtin.Int64, Builtin.Int64) -> Builtin.Int1 {
+bb0(%0 : $Builtin.Int64, %1 : $Builtin.Int64):
+  %2 = builtin "cmp_ne_Int64"(%0, %1) : $Builtin.Int1
+  %3 = integer_literal $Builtin.Int1, -1
+  %4 = builtin "xor_Int1"(%2, %3) : $Builtin.Int1
+  return %4
+}
+
+// CHECK-LABEL: sil @invert_comparison_sle :
+// CHECK:         %2 = builtin "cmp_sgt_Int64"(%0 : $Builtin.Int64, %1 : $Builtin.Int64)
+// CHECK:         return %2
+// CHECK:       } // end sil function 'invert_comparison_sle'
+sil @invert_comparison_sle : $@convention(thin) (Builtin.Int64, Builtin.Int64) -> Builtin.Int1 {
+bb0(%0 : $Builtin.Int64, %1 : $Builtin.Int64):
+  %2 = builtin "cmp_sle_Int64"(%0, %1) : $Builtin.Int1
+  %3 = integer_literal $Builtin.Int1, -1
+  %4 = builtin "xor_Int1"(%2, %3) : $Builtin.Int1
+  return %4
+}
+
+// CHECK-LABEL: sil @invert_comparison_slt :
+// CHECK:         %2 = builtin "cmp_sge_Int64"(%0 : $Builtin.Int64, %1 : $Builtin.Int64)
+// CHECK:         return %2
+// CHECK:       } // end sil function 'invert_comparison_slt'
+sil @invert_comparison_slt : $@convention(thin) (Builtin.Int64, Builtin.Int64) -> Builtin.Int1 {
+bb0(%0 : $Builtin.Int64, %1 : $Builtin.Int64):
+  %2 = builtin "cmp_slt_Int64"(%0, %1) : $Builtin.Int1
+  %3 = integer_literal $Builtin.Int1, -1
+  %4 = builtin "xor_Int1"(%2, %3) : $Builtin.Int1
+  return %4
+}
+
+// CHECK-LABEL: sil @invert_comparison_sge :
+// CHECK:         %2 = builtin "cmp_slt_Int64"(%0 : $Builtin.Int64, %1 : $Builtin.Int64)
+// CHECK:         return %2
+// CHECK:       } // end sil function 'invert_comparison_sge'
+sil @invert_comparison_sge : $@convention(thin) (Builtin.Int64, Builtin.Int64) -> Builtin.Int1 {
+bb0(%0 : $Builtin.Int64, %1 : $Builtin.Int64):
+  %2 = builtin "cmp_sge_Int64"(%0, %1) : $Builtin.Int1
+  %3 = integer_literal $Builtin.Int1, -1
+  %4 = builtin "xor_Int1"(%2, %3) : $Builtin.Int1
+  return %4
+}
+
+// CHECK-LABEL: sil @invert_comparison_sgt :
+// CHECK:         %2 = builtin "cmp_sle_Int64"(%0 : $Builtin.Int64, %1 : $Builtin.Int64)
+// CHECK:         return %2
+// CHECK:       } // end sil function 'invert_comparison_sgt'
+sil @invert_comparison_sgt : $@convention(thin) (Builtin.Int64, Builtin.Int64) -> Builtin.Int1 {
+bb0(%0 : $Builtin.Int64, %1 : $Builtin.Int64):
+  %2 = builtin "cmp_sgt_Int64"(%0, %1) : $Builtin.Int1
+  %3 = integer_literal $Builtin.Int1, -1
+  %4 = builtin "xor_Int1"(%2, %3) : $Builtin.Int1
+  return %4
+}
+
+// CHECK-LABEL: sil @invert_comparison_ule :
+// CHECK:         %2 = builtin "cmp_ugt_Int64"(%0 : $Builtin.Int64, %1 : $Builtin.Int64)
+// CHECK:         return %2
+// CHECK:       } // end sil function 'invert_comparison_ule'
+sil @invert_comparison_ule : $@convention(thin) (Builtin.Int64, Builtin.Int64) -> Builtin.Int1 {
+bb0(%0 : $Builtin.Int64, %1 : $Builtin.Int64):
+  %2 = builtin "cmp_ule_Int64"(%0, %1) : $Builtin.Int1
+  %3 = integer_literal $Builtin.Int1, -1
+  %4 = builtin "xor_Int1"(%2, %3) : $Builtin.Int1
+  return %4
+}
+
+// CHECK-LABEL: sil @invert_comparison_ult :
+// CHECK:         %2 = builtin "cmp_uge_Int64"(%0 : $Builtin.Int64, %1 : $Builtin.Int64)
+// CHECK:         return %2
+// CHECK:       } // end sil function 'invert_comparison_ult'
+sil @invert_comparison_ult : $@convention(thin) (Builtin.Int64, Builtin.Int64) -> Builtin.Int1 {
+bb0(%0 : $Builtin.Int64, %1 : $Builtin.Int64):
+  %2 = builtin "cmp_ult_Int64"(%0, %1) : $Builtin.Int1
+  %3 = integer_literal $Builtin.Int1, -1
+  %4 = builtin "xor_Int1"(%2, %3) : $Builtin.Int1
+  return %4
+}
+
+// CHECK-LABEL: sil @invert_comparison_uge :
+// CHECK:         %2 = builtin "cmp_ult_Int64"(%0 : $Builtin.Int64, %1 : $Builtin.Int64)
+// CHECK:         return %2
+// CHECK:       } // end sil function 'invert_comparison_uge'
+sil @invert_comparison_uge : $@convention(thin) (Builtin.Int64, Builtin.Int64) -> Builtin.Int1 {
+bb0(%0 : $Builtin.Int64, %1 : $Builtin.Int64):
+  %2 = builtin "cmp_uge_Int64"(%0, %1) : $Builtin.Int1
+  %3 = integer_literal $Builtin.Int1, -1
+  %4 = builtin "xor_Int1"(%2, %3) : $Builtin.Int1
+  return %4
+}
+
+// CHECK-LABEL: sil @invert_comparison_ugt :
+// CHECK:         %2 = builtin "cmp_ule_Int64"(%0 : $Builtin.Int64, %1 : $Builtin.Int64)
+// CHECK:         return %2
+// CHECK:       } // end sil function 'invert_comparison_ugt'
+sil @invert_comparison_ugt : $@convention(thin) (Builtin.Int64, Builtin.Int64) -> Builtin.Int1 {
+bb0(%0 : $Builtin.Int64, %1 : $Builtin.Int64):
+  %2 = builtin "cmp_ugt_Int64"(%0, %1) : $Builtin.Int1
+  %3 = integer_literal $Builtin.Int1, -1
+  %4 = builtin "xor_Int1"(%2, %3) : $Builtin.Int1
+  return %4
+}
+
+// CHECK-LABEL: sil @no_invert_wrong_literal :
+// CHECK:         builtin "cmp_ugt_Int64"
+// CHECK:       } // end sil function 'no_invert_wrong_literal'
+sil @no_invert_wrong_literal : $@convention(thin) (Builtin.Int64, Builtin.Int64) -> Builtin.Int1 {
+bb0(%0 : $Builtin.Int64, %1 : $Builtin.Int64):
+  %2 = builtin "cmp_ugt_Int64"(%0, %1) : $Builtin.Int1
+  %3 = integer_literal $Builtin.Int1, 0
+  %4 = builtin "xor_Int1"(%2, %3) : $Builtin.Int1
+  return %4
+}
+
+// CHECK-LABEL: sil @no_invert_unknown_rhs :
+// CHECK:         builtin "cmp_ugt_Int64"
+// CHECK:       } // end sil function 'no_invert_unknown_rhs'
+sil @no_invert_unknown_rhs : $@convention(thin) (Builtin.Int64, Builtin.Int64, Builtin.Int1) -> Builtin.Int1 {
+bb0(%0 : $Builtin.Int64, %1 : $Builtin.Int64, %2 : $Builtin.Int1):
+  %3 = builtin "cmp_ugt_Int64"(%0, %1) : $Builtin.Int1
+  %4 = builtin "xor_Int1"(%3, %2) : $Builtin.Int1
+  return %4
+}
+
+// CHECK-LABEL: sil @no_invert_no_comparison :
+// CHECK:         %2 = builtin "xor_Int1"
+// CHECK:         return %2
+// CHECK:       } // end sil function 'no_invert_no_comparison'
+sil @no_invert_no_comparison : $@convention(thin) (Builtin.Int1) -> Builtin.Int1 {
+bb0(%0 : $Builtin.Int1):
+  %1 = integer_literal $Builtin.Int1, -1
+  %2 = builtin "xor_Int1"(%0, %1) : $Builtin.Int1
+  return %2
+}
+
+// CHECK-LABEL: sil @no_invert_wrong_comparison :
+// CHECK:         builtin "fcmp_ord_FPIEEE32"
+// CHECK:       } // end sil function 'no_invert_wrong_comparison'
+sil @no_invert_wrong_comparison : $@convention(thin) (Builtin.FPIEEE32, Builtin.FPIEEE32) -> Builtin.Int1 {
+bb0(%0 : $Builtin.FPIEEE32, %1 : $Builtin.FPIEEE32):
+  %2 = builtin "fcmp_ord_FPIEEE32"(%0 : $Builtin.FPIEEE32, %1 : $Builtin.FPIEEE32) : $Builtin.Int1
+  %3 = integer_literal $Builtin.Int1, -1
+  %4 = builtin "xor_Int1"(%2, %3) : $Builtin.Int1
+  return %4
+}
+
diff --git a/test/SILOptimizer/span_bounds_check_tests.swift b/test/SILOptimizer/span_bounds_check_tests.swift
index 99522d0113b7e..0d7bbd5d493d4 100644
--- a/test/SILOptimizer/span_bounds_check_tests.swift
+++ b/test/SILOptimizer/span_bounds_check_tests.swift
@@ -353,3 +353,18 @@ public func inout_span_sum_iterate_to_unknown_with_trap_dontopt(_ v: inout Span<
   return sum
 }
 
+// Check that the loop is fully optimized, including bounds check elimination and vectorization.
+
+// CHECK-IR-LABEL: define {{.*}} @"$s4test4loop4over5usingSis4SpanVys5UInt8VG_AFySiGtF"
+// CHECK-IR:       vector.body:
+// CHECK-IR:       ret
+public func loop(over a: borrowing Span<UInt8>, using b: borrowing Span<Int>) -> Int {
+  var result = 0
+  precondition(UInt8.max < b.count)
+  for i in a.indices {
+    let idx = Int(a[i])
+    result &+= b[idx]
+  }
+  return result
+}
+