Propagate NSW in ~((-X) | Y) --> (X - 1) & (~Y)

https://alive2.llvm.org/ce/z/qojyPF

If -X is nsw, then X - 1 must be too.
This is because -X can only be nsw if X is any number that is not
INT_MIN. And if X is not INT_MIN, then X - 1 must be nsw.

Author: AZero13

llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp

@@ -4750,8 +4750,22 @@ Instruction *InstCombinerImpl::foldNot(BinaryOperator &I) {
   BinaryOperator *NotVal;
   if (match(NotOp, m_BinOp(NotVal))) {
     // ~((-X) | Y) --> (X - 1) & (~Y)
+    if (match(NotVal,
+              m_OneUse(m_c_Or(m_OneUse(m_NSWNeg(m_Value(X))), m_Value(Y))))) {
+      // If -X is nsw, then X - 1 must be too.
+      // This is because -X can only be nsw if X is any number that is not
+      // INT_MIN. And if X is not INT_MIN, then X - 1 must be nsw.
+      Value *DecX = Builder.CreateAdd(X, ConstantInt::getAllOnesValue(Ty), "",
+                                      /*HasNUW=*/false, /*HasNSW=*/true);
+      Value *NotY = Builder.CreateNot(Y);
+      return BinaryOperator::CreateAnd(DecX, NotY);
+    }
+
     if (match(NotVal,
               m_OneUse(m_c_Or(m_OneUse(m_Neg(m_Value(X))), m_Value(Y))))) {
+      // If -X is nsw, then X - 1 must be too.
+      // This is because -X can only be nsw if X is any number that is not
+      // INT_MIN. And if X is not INT_MIN, then X - 1 must be nsw.
       Value *DecX = Builder.CreateAdd(X, ConstantInt::getAllOnesValue(Ty));
       Value *NotY = Builder.CreateNot(Y);
       return BinaryOperator::CreateAnd(DecX, NotY);

llvm/test/Transforms/InstCombine/not.ll

@@ -438,7 +438,7 @@ define <3 x i5> @not_or_neg_commute_vec(<3 x i5> %x, <3 x i5> %p)  {
 
 define i8 @not_or_neg_nsw(i8 %x, i8 %y)  {
 ; CHECK-LABEL: @not_or_neg_nsw(
-; CHECK-NEXT:    [[TMP1:%.*]] = add i8 [[Y:%.*]], -1
+; CHECK-NEXT:    [[TMP1:%.*]] = add nsw i8 [[Y:%.*]], -1
 ; CHECK-NEXT:    [[TMP2:%.*]] = xor i8 [[X:%.*]], -1
 ; CHECK-NEXT:    [[NOT:%.*]] = and i8 [[TMP1]], [[TMP2]]
 ; CHECK-NEXT:    ret i8 [[NOT]]
@@ -452,7 +452,7 @@ define i8 @not_or_neg_nsw(i8 %x, i8 %y)  {
 define <3 x i5> @not_or_neg_commute_vec_nsw(<3 x i5> %x, <3 x i5> %p)  {
 ; CHECK-LABEL: @not_or_neg_commute_vec_nsw(
 ; CHECK-NEXT:    [[Y:%.*]] = mul <3 x i5> [[P:%.*]], <i5 1, i5 2, i5 3>
-; CHECK-NEXT:    [[TMP1:%.*]] = add <3 x i5> [[X:%.*]], splat (i5 -1)
+; CHECK-NEXT:    [[TMP1:%.*]] = add nsw <3 x i5> [[X:%.*]], splat (i5 -1)
 ; CHECK-NEXT:    [[TMP2:%.*]] = xor <3 x i5> [[Y]], splat (i5 -1)
 ; CHECK-NEXT:    [[NOT:%.*]] = and <3 x i5> [[TMP1]], [[TMP2]]
 ; CHECK-NEXT:    ret <3 x i5> [[NOT]]