[inductor] Prevent aggressive fusion during inductor lowering (#87447)
Fixes https://github.com/pytorch/torchdynamo/issues/1599
Inductor performs aggressive fusion of ops during the lowering of Fx graph into IR nodes. Note that this fusion is different from the fusion that we typically discuss in the context of Inductor, which refers to the fusion of SchedulerNodes (way after lowering). This PR, instead, ensures that we don't accumulate too many ops in the IR node to begin with.
In the case of hf_t5_large backward graph, earlier we would generate a kernel with 100s of operators, causing that kernel to take ~350 seconds of compilation time. With this PR, we get it down from 350 seconds to 50 seconds.
Note that this could affect performance. I doubt that it will lead to really large dip though. In my toy examples, even if the lowering creates multiple IR nodes, if its a simple fusion, later fusion still creates one node.
I would like (1) test_torchinductor.py, (2) test_torchinductor_info.py, and (3) atleast HF models to be enabled in CI before merging this one.
@ngimel @jansel @Chillee
cc @jansel @lezcano @fdrocha @mlazos @soumith @voznesenskym @yanboliang @penguinwu
Pull Request resolved: https://github.com/pytorch/pytorch/pull/87447
Approved by: https://github.com/jansel
