Index: llvm/lib/Analysis/InstructionSimplify.cpp
===================================================================
--- llvm/lib/Analysis/InstructionSimplify.cpp
+++ llvm/lib/Analysis/InstructionSimplify.cpp
@@ -766,6 +766,13 @@
   if (Op0 == Op1)
     return Constant::getNullValue(Op0->getType());
 
+  // if (X == Y)
+  //     X - Y -> 0
+  Optional<bool> Imp =
+      isImpliedByDomCondition(CmpInst::ICMP_EQ, Op0, Op1, Q.CxtI, Q.DL);
+  if (Imp)
+    return Constant::getNullValue(Op0->getType());
+
   // Is this a negation?
   if (match(Op0, m_Zero())) {
     // 0 - X -> 0 if the sub is NUW.
@@ -2480,6 +2487,13 @@
   if (Op0 == Op1)
     return Constant::getNullValue(Op0->getType());
 
+  // if (A == B)
+  //     A ^ B -> 0
+  Optional<bool> Imp =
+      isImpliedByDomCondition(CmpInst::ICMP_EQ, Op0, Op1, Q.CxtI, Q.DL);
+  if (Imp)
+    return Constant::getNullValue(Op0->getType());
+
   // A ^ ~A  =  ~A ^ A  =  -1
   if (match(Op0, m_Not(m_Specific(Op1))) || match(Op1, m_Not(m_Specific(Op0))))
     return Constant::getAllOnesValue(Op0->getType());
Index: llvm/test/Transforms/InstSimplify/domcondition.ll
===================================================================
--- /dev/null
+++ llvm/test/Transforms/InstSimplify/domcondition.ll
@@ -0,0 +1,75 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
+; RUN: opt < %s -passes=instsimplify -S | FileCheck %s
+
+define i32 @xor_domcondition(i32 %x, i32 %y) {
+; CHECK-LABEL: @xor_domcondition(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    [[CMP:%.*]] = icmp eq i32 [[X:%.*]], [[Y:%.*]]
+; CHECK-NEXT:    br i1 [[CMP]], label [[COND_TRUE:%.*]], label [[COND_END:%.*]]
+; CHECK:       cond.true:
+; CHECK-NEXT:    br label [[COND_END]]
+; CHECK:       cond.end:
+; CHECK-NEXT:    ret i32 0
+;
+entry:
+  %cmp = icmp eq i32 %x, %y
+  br i1 %cmp, label %cond.true, label %cond.end
+
+cond.true:
+  %xor = xor i32 %x, %y
+  %mul = mul i32 %xor, %x
+  br label %cond.end
+
+cond.end:
+  %cond = phi i32 [ %mul, %cond.true ], [ 0, %entry ]
+  ret i32 %cond
+}
+
+define i32 @xor_domcondition_negative(i32 %x, i32 %y) {
+; CHECK-LABEL: @xor_domcondition_negative(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    [[CMP:%.*]] = icmp ne i32 [[X:%.*]], [[Y:%.*]]
+; CHECK-NEXT:    br i1 [[CMP]], label [[COND_TRUE:%.*]], label [[COND_END:%.*]]
+; CHECK:       cond.true:
+; CHECK-NEXT:    br label [[COND_END]]
+; CHECK:       cond.end:
+; CHECK-NEXT:    ret i32 0
+;
+entry:
+  %cmp = icmp ne i32 %x, %y
+  br i1 %cmp, label %cond.true, label %cond.end
+
+cond.true:
+  %xor = xor i32 %x, %y
+  %mul = mul i32 %xor, %x
+  br label %cond.end
+
+cond.end:
+  %cond = phi i32 [ %mul, %cond.true ], [ 0, %entry ]
+  ret i32 %cond
+}
+
+
+define i32 @sub_domcondition(i32 %x, i32 %y) {
+; CHECK-LABEL: @sub_domcondition(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    [[CMP:%.*]] = icmp eq i32 [[X:%.*]], [[Y:%.*]]
+; CHECK-NEXT:    br i1 [[CMP]], label [[COND_TRUE:%.*]], label [[COND_END:%.*]]
+; CHECK:       cond.true:
+; CHECK-NEXT:    br label [[COND_END]]
+; CHECK:       cond.end:
+; CHECK-NEXT:    ret i32 0
+;
+entry:
+  %cmp = icmp eq i32 %x, %y
+  br i1 %cmp, label %cond.true, label %cond.end
+
+cond.true:
+  %xor = xor i32 %x, %y
+  %mul = mul i32 %xor, %x
+  br label %cond.end
+
+cond.end:
+  %cond = phi i32 [ %mul, %cond.true ], [ 0, %entry ]
+  ret i32 %cond
+}