[llvm] Handle ISD::ABDS in SelectionDAG::ComputeNumSignBits (PR #175321)

[Craig Topper via llvm-commits]

================
@@ -338,6 +338,57 @@ TEST_F(AArch64SelectionDAGTest, ComputeNumSignBits_ADDC) {
   EXPECT_EQ(DAG->ComputeNumSignBits(Op), 2u);
 }
 
+TEST_F(AArch64SelectionDAGTest, ComputeNumSignBits_ABDS) {
----------------
topperc wrote:

Unless, I'm mistaken these tests already pass on trunk. Probably because computeNumSignBits falls back to computeKnownBits which knows the result is a positive number with `Known.Zero.setHighBits(std::min(SignBits0, SignBits1) - 1);`

https://github.com/llvm/llvm-project/pull/175321