Cranelift: remove non-egraphs optimization pipeline and use_egraphs option.
#6167
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… option. This PR removes the LICM, GVN, and preopt passes, and associated support pieces, from `cranelift-codegen`. Not to worry, we still have optimizations: the egraph framework subsumes all of these, and has been on by default since bytecodealliance#5181. A few decision points: - Filetests for the legacy LICM, GVN and simple_preopt were removed too. As we built optimizations in the egraph framework we wrote new tests for the equivalent functionality, and many of the old tests were testing specific behaviors in the old implementations that may not be relevant anymore. However if folks prefer I could take a different approach here and try to port over all of the tests. - The corresponding filetest modes (commands) were deleted too. The `test alias_analysis` mode remains, but no longer invokes a separate GVN first (since there is no separate GVN that will not also do alias analysis) so the tests were tweaked slightly to work with that. The egrpah testsuite also covers alias analysis. - The `divconst_magic_numbers` module is removed since it's unused without `simple_preopt`, though this is the one remaining optimization we still need to build in the egraphs framework, pending bytecodealliance#5908. The magic numbers will live forever in git history so removing this in the meantime is not a major issue IMHO. - The `use_egraphs` setting itself was removed at both the Cranelift and Wasmtime levels. It has been marked deprecated for a few releases now (Wasmtime 6.0, 7.0, upcoming 8.0, and corresponding Cranelift versions) so I think this is probably OK. As an alternative if anyone feels strongly, we could leave the setting and make it a no-op.
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| /// Fold comparisons into branch operations when possible. | ||
| /// | ||
| /// This matches against operations which compare against zero, then use the | ||
| /// result in a conditional branch. | ||
| fn branch_opt(pos: &mut FuncCursor, inst: Inst) { |
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I think we're still unable to port this optimization to egraphs. That shouldn't block this PR, but it would be nice to optimize control flow in the future as well :)
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Ah, yes, it looks like this is doing (brif (icmp eq a 0) ...) -> (brif a ...) and the equivalent for ne -- that would indeed be useful to have someday!
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Specifically, that issue is tracked in #6106.
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… option. (bytecodealliance#6167) * Cranelift: remove non-egraphs optimization pipeline and `use_egraphs` option. This PR removes the LICM, GVN, and preopt passes, and associated support pieces, from `cranelift-codegen`. Not to worry, we still have optimizations: the egraph framework subsumes all of these, and has been on by default since bytecodealliance#5181. A few decision points: - Filetests for the legacy LICM, GVN and simple_preopt were removed too. As we built optimizations in the egraph framework we wrote new tests for the equivalent functionality, and many of the old tests were testing specific behaviors in the old implementations that may not be relevant anymore. However if folks prefer I could take a different approach here and try to port over all of the tests. - The corresponding filetest modes (commands) were deleted too. The `test alias_analysis` mode remains, but no longer invokes a separate GVN first (since there is no separate GVN that will not also do alias analysis) so the tests were tweaked slightly to work with that. The egrpah testsuite also covers alias analysis. - The `divconst_magic_numbers` module is removed since it's unused without `simple_preopt`, though this is the one remaining optimization we still need to build in the egraphs framework, pending bytecodealliance#5908. The magic numbers will live forever in git history so removing this in the meantime is not a major issue IMHO. - The `use_egraphs` setting itself was removed at both the Cranelift and Wasmtime levels. It has been marked deprecated for a few releases now (Wasmtime 6.0, 7.0, upcoming 8.0, and corresponding Cranelift versions) so I think this is probably OK. As an alternative if anyone feels strongly, we could leave the setting and make it a no-op. * Update test outputs for remaining test differences.
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This PR removes the LICM, GVN, and preopt passes, and associated support pieces, from
cranelift-codegen. Not to worry, we still have optimizations: the egraph framework subsumes all of these, and has been on by default since #5181.A few decision points:
Filetests for the legacy LICM, GVN and simple_preopt were removed too. As we built optimizations in the egraph framework we wrote new tests for the equivalent functionality, and many of the old tests were testing specific behaviors in the old implementations that may not be relevant anymore. However if folks prefer I could take a different approach here and try to port over all of the tests.
The corresponding filetest modes (commands) were deleted too. The
test alias_analysismode remains, but no longer invokes a separate GVN first (since there is no separate GVN that will not also do alias analysis) so the tests were tweaked slightly to work with that. The egrpah testsuite also covers alias analysis.The
divconst_magic_numbersmodule is removed since it's unused withoutsimple_preopt, though this is the one remaining optimization we still need to build in the egraphs framework, pending cranelift/egraphs: allow simplifying trapping arithmetic #5908. The magic numbers will live forever in git history so removing this in the meantime is not a major issue IMHO.The
use_egraphssetting itself was removed at both the Cranelift and Wasmtime levels. It has been marked deprecated for a few releases now (Wasmtime 6.0, 7.0, upcoming 8.0, and corresponding Cranelift versions) so I think this is probably OK. As an alternative if anyone feels strongly, we could leave the setting and make it a no-op.