[llvm] [GlobalISel] port rewrite from SelectionDAG to GlobalISel (PR #181486)

[Luisa Cicolini via llvm-commits]

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@@ -1879,6 +1879,26 @@ def APlusBMinusCMinusB : GICombineRule<
           (G_SUB $root, $add1, $B)),
    (apply (G_SUB $root, $A, $C))>;
 
+// fold ((A+(B+C))-B) -> A+C
+def APlusBPlusCMinusB_frags : GICombinePatFrag<
+  (outs root:$root), (ins $x, $y, $n),
+  [
+    (pattern (G_ADD $add1, $y, $n),
+              (G_ADD $add2, $x, $add1),
+              (G_SUB $root, $add2, $y),
+             [{ return MRI.hasOneNonDBGUse(${add2}.getReg()) &&
+                       MRI.hasOneNonDBGUse(${add1}.getReg()); }]),
+  ]>;
+
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luisacicolini wrote:

```suggestion
```

https://github.com/llvm/llvm-project/pull/181486