[llvm] [GlobalISel] Add G_SUB for computeNumSignBits (PR #158384)

[Yatao Wang via llvm-commits]

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@@ -177,6 +177,51 @@ TEST_F(AArch64SelectionDAGTest, ComputeNumSignBits_VASHR) {
   EXPECT_EQ(DAG->ComputeNumSignBits(Fr2), 5u);
 }
 
+TEST_F(AArch64SelectionDAGTest, ComputeNumSignBits_SUB) {
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ningxinr wrote:

Hi David, would you still prefer that I remove the `SelectionDAG` test from this change? 

https://github.com/llvm/llvm-project/pull/158384