Index: llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
===================================================================
--- llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
+++ llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
@@ -1479,6 +1479,33 @@
        match(RHS, m_ZExt(m_NUWSub(m_Value(B), m_Specific(A))))))
     return new ZExtInst(B, LHS->getType());
 
+  // Fold the following:
+  // X = select A, T_C, F_C
+  // Z = zext A or Z = sext A
+  // W = add X, Z
+  // =>
+  // select A, T_C + 1, F_C (for Z = zext A)
+  // select A, T_C - 1, F_C (for Z = sext A)
+  // Take into account the negation as well.
+  Value *CondVal;
+  Constant *TrueC, *FalseC;
+  if ((match(RHS, m_ZExtOrSExt(m_Value(A))) &&
+       A->getType()->getScalarSizeInBits() == 1) &&
+      match(LHS, m_Select(m_Value(CondVal), m_ImmConstant(TrueC),
+                          m_ImmConstant(FalseC)))) {
+    if (CondVal == A) {
+      if (isa<ZExtInst>(RHS))
+        return SelectInst::Create(CondVal, InstCombiner::AddOne(TrueC), FalseC);
+      return SelectInst::Create(CondVal, InstCombiner::SubOne(TrueC), FalseC);
+    }
+
+    if (match(A, m_Not(m_Specific(CondVal)))) {
+      if (isa<ZExtInst>(RHS))
+        return SelectInst::Create(CondVal, TrueC, InstCombiner::AddOne(FalseC));
+      return SelectInst::Create(CondVal, TrueC, InstCombiner::SubOne(FalseC));
+    }
+  }
+
   // A+B --> A|B iff A and B have no bits set in common.
   if (haveNoCommonBitsSet(LHS, RHS, DL, &AC, &I, &DT))
     return BinaryOperator::CreateOr(LHS, RHS);
Index: llvm/test/Transforms/InstCombine/add.ll
===================================================================
--- llvm/test/Transforms/InstCombine/add.ll
+++ llvm/test/Transforms/InstCombine/add.ll
@@ -3019,4 +3019,50 @@
   ret <2 x i32> %c
 }
 
+define i64 @add_select_zext(i1 %c) {
+; CHECK-LABEL: @add_select_zext(
+; CHECK-NEXT:    [[ADD:%.*]] = select i1 [[C:%.*]], i64 65, i64 1
+; CHECK-NEXT:    ret i64 [[ADD]]
+;
+  %sel = select i1 %c, i64 64, i64 1
+  %ext = zext i1 %c to i64
+  %add = add i64 %sel, %ext
+  ret i64 %add
+}
+
+define i64 @add_select_sext(i1 %c) {
+; CHECK-LABEL: @add_select_sext(
+; CHECK-NEXT:    [[ADD:%.*]] = select i1 [[C:%.*]], i64 63, i64 1
+; CHECK-NEXT:    ret i64 [[ADD]]
+;
+  %sel = select i1 %c, i64 64, i64 1
+  %ext = sext i1 %c to i64
+  %add = add i64 %sel, %ext
+  ret i64 %add
+}
+
+define i64 @add_select_not_zext(i1 %c) {
+; CHECK-LABEL: @add_select_not_zext(
+; CHECK-NEXT:    [[ADD:%.*]] = select i1 [[C:%.*]], i64 64, i64 2
+; CHECK-NEXT:    ret i64 [[ADD]]
+;
+  %sel = select i1 %c, i64 64, i64 1
+  %not.c = xor i1 %c, true
+  %ext = zext i1 %not.c to i64
+  %add = add i64 %sel, %ext
+  ret i64 %add
+}
+
+define i64 @add_select_not_sext(i1 %c) {
+; CHECK-LABEL: @add_select_not_sext(
+; CHECK-NEXT:    [[ADD:%.*]] = select i1 [[C:%.*]], i64 64, i64 0
+; CHECK-NEXT:    ret i64 [[ADD]]
+;
+  %sel = select i1 %c, i64 64, i64 1
+  %not.c = xor i1 %c, true
+  %ext = sext i1 %not.c to i64
+  %add = add i64 %sel, %ext
+  ret i64 %add
+}
+
 declare void @llvm.assume(i1)