[llvm] [GlobalISel] Handle div-by-pow2 (PR #83155)

[Kai Nacke via llvm-commits]

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@@ -1005,7 +1005,13 @@ def sdiv_by_const : GICombineRule<
    [{ return Helper.matchSDivByConst(*${root}); }]),
   (apply [{ Helper.applySDivByConst(*${root}); }])>;
 
-def intdiv_combines : GICombineGroup<[udiv_by_const, sdiv_by_const]>;
+def sdiv_by_pow2 : GICombineRule<
+  (defs root:$root),
+  (match (wip_match_opcode G_SDIV):$root,
+   [{ return Helper.matchSDivByPow2(*${root}); }]),
+  (apply [{ Helper.applySDivByPow2(*${root}); }])>;
+
+def intdiv_combines : GICombineGroup<[udiv_by_const, sdiv_by_const, sdiv_by_pow2]>;
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redstar wrote:

`sdiv_by_pow2` matches a true subset of `sdiv_by_const`. Is there some guarantee which rules matches?
The SelectionDAG pattern matcher uses lexcial order, which can be influenced with a priority. I did not see anything about it in the [docs](https://llvm.org/docs/GlobalISel/MIRPatterns.html), but I may have overlooked it.

https://github.com/llvm/llvm-project/pull/83155