[llvm] [NVPTX][SelectionDAG] Add IMAD combine rules + infra to disable default SelectionDAG rules for testing (PR #121724)

[via llvm-commits]

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@@ -153,6 +153,13 @@ static cl::opt<bool> EnableVectorFCopySignExtendRound(
     "combiner-vector-fcopysign-extend-round", cl::Hidden, cl::init(false),
     cl::desc(
         "Enable merging extends and rounds into FCOPYSIGN on vector types"));
+
+static cl::opt<bool>
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peterbell10 wrote:

Yes. I've included a test for the sdiv pattern mentioned in the PR description, but it's a bit fragile as it depends on the interaction of several unrelated patterns applied in a specific order. My intention is to test the mad combiner code in isolation. 

I think the ideal way would be if I could input the SelectionDAG directly from a text input, but this seems like the next-best thing; translating the LLVM IR literally into SelectionDAG nodes without alteration.

https://github.com/llvm/llvm-project/pull/121724