[InstCombine] Preserve the nsw/nuw flags for (X | Op01C) + Op1C --> X + (Op01C + Op1C) (#94586)

This patch simplifies `sdiv` to `udiv` by preserving the `nsw` flag for
`(X | Op01C) + Op1C --> X + (Op01C + Op1C)` if the sum of `Op01C` and
`Op1C` will not overflow, and preserves the `nuw` flag unconditionally.

Alive2 Proofs (provided by @nikic): https://alive2.llvm.org/ce/z/nrdCZT,
https://alive2.llvm.org/ce/z/YnJHnH

1 files changed, 8 insertions, 2 deletions

diff --git a/llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp b/llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
index 8205b49..0a73c58 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
@@ -905,8 +905,14 @@ Instruction *InstCombinerImpl::foldAddWithConstant(BinaryOperator &Add) {
 
   // (X | Op01C) + Op1C --> X + (Op01C + Op1C) iff the `or` is actually an `add`
   Constant *Op01C;
-  if (match(Op0, m_DisjointOr(m_Value(X), m_ImmConstant(Op01C))))
-    return BinaryOperator::CreateAdd(X, ConstantExpr::getAdd(Op01C, Op1C));
+  if (match(Op0, m_DisjointOr(m_Value(X), m_ImmConstant(Op01C)))) {
+    BinaryOperator *NewAdd =
+        BinaryOperator::CreateAdd(X, ConstantExpr::getAdd(Op01C, Op1C));
+    NewAdd->setHasNoSignedWrap(Add.hasNoSignedWrap() &&
+                               willNotOverflowSignedAdd(Op01C, Op1C, Add));
+    NewAdd->setHasNoUnsignedWrap(Add.hasNoUnsignedWrap());
+    return NewAdd;
+  }
 
   // (X | C2) + C --> (X | C2) ^ C2 iff (C2 == -C)
   const APInt *C2;