Strip asserts right at the end of lowering #8094
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The simplifier exploits asserts to make simplification. When compiling with NoAsserts, certain assertions aren't ever introduced, which means that the simplifier can't exploit certain things that we know to be true. Mostly this has a negative effect on code size. E.g. tail cases get generated even though they are actually dead code. This PR keeps all the assertions right until the end of lowering, when it strips them in a dedicated pass. This reduces object file size for a large production blob of Halide code by ~10%, without measurably affecting runtime.
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I expect we'll need to make sure this doesn't introduce any failures in our large codebase before it lands. |
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To be clear, this shouldn't affect code that isn't compiled with NoAsserts (ie. the vast majority of code), right? |
| @@ -427,6 +428,12 @@ void lower_impl(const vector<Function> &output_funcs, | |||
| s = hoist_prefetches(s); | |||
| log("Lowering after hoisting prefetches:", s); | |||
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| if (t.has_feature(Target::NoAsserts)) { | |||
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Might be worth adding comment from the PR about why we do this at the end
That's correct. This should have no effect on regular assert-using Halide code. |
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No related failures yet, going to run an all-of-google test just to be sure |
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The simplifier exploits asserts to make simplifications. When compiling with NoAsserts, certain assertions aren't ever introduced, which means that the simplifier can't exploit certain things that we know to be true. Mostly this has a negative effect on code size. E.g. tail cases get generated even though they are actually dead code.
This PR keeps all the assertions right until the end of lowering, when it strips them in a dedicated pass.
This reduces object file size for a large production blob of Halide code by ~10%, without measurably affecting runtime.