Disable the SimplifyArmIdentity pass
#73262
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r? @eddyb (rust_highfive has picked a reviewer for you, use r? to override) |
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rust-highfive
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If we aren't in a rush about this, please open a PR against master with this change that we can backport to beta. |
This pass is buggy so I'm disabling it to fix a stable-to-beta regression. Related to rust-lang#73223
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☔ The latest upstream changes made this pull request unmergeable. Please resolve the merge conflicts. |
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Rebased |
oli-obk
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@bors r+ |
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📌 Commit f160583 has been approved by |
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Since the linked PR is @bors p=1 |
Mark-Simulacrum
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SimplifyArmIdentity pass on betaSimplifyArmIdentity pass
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bumping this higher to run after the current rollup @bors p=3 |
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⌛ Testing commit f160583 with merge 664f6df82aa3cc4f3ad1eec7dd277b061938f7da... |
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💔 Test failed - checks-azure |
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@bors retry |
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@bors retry |
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@bors retru p=1000 |
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@bors retry p=1000 |
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@bors treeclosed- |
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@bors treeclosed-- |
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☀️ Test successful - checks-azure |
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This caused a small perf regression in a couple of @wesleywiser: will this pass be re-enabled in the future? |
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@nnethercote Yes! I'm working on finishing up some changes that will re-enable this on nightly. |
spastorino
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The manner in which this was disabled seems relevant to a recent wg-mir-opt conversation on zulip. I guess if opt-level >= 2 is generally known to denote potentially buggy optimizations, then what's done here is okay. But I don't know if that's the consensus based on the above linked conversation... |
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(I was tempted to unilaterally beta approve this, but I'm hesitating due to not knowing if it matches the semantics everyone else expects from the mir-opt levels. We'll just discuss as a group tomorrow instead.) |
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@pnkfelix The current state is that |
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@wesleywiser I presume you'll add some tests that demonstrate the bug, too? |
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@nikomatsakis Yes, I'm adding some regression tests in the next PR. |
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Discussed at T-compiler meeting; approved for beta backport |
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| @@ -306,7 +306,11 @@ fn optimization_applies<'tcx>( | |||
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| impl<'tcx> MirPass<'tcx> for SimplifyArmIdentity { | |||
| fn run_pass(&self, _: TyCtxt<'tcx>, source: MirSource<'tcx>, body: &mut Body<'tcx>) { | |||
| fn run_pass(&self, tcx: TyCtxt<'tcx>, source: MirSource<'tcx>, body: &mut Body<'tcx>) { | |||
| if tcx.sess.opts.debugging_opts.mir_opt_level < 2 { | |||
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Uh, could we maybe not keep buggy passes running at all? I think a -Zmir-opt-level=3 miscompilation is a soundness bug just like it would be at a lower optimization level.
C/C++ programmers seem to associate "high optimization levels" with "creates buggy code", but really that's awful and we shouldn't do it.
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@RalfJung I opened a related MCP: rust-lang/compiler-team#319
If you have thoughts about it, please leave a comment there. Thanks!
Mark-Simulacrum
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…ulacrum [beta] backports This PR backports the following: * Make novel structural match violations not a `bug` rust-lang#73446 * linker: Never pass `-no-pie` to non-gnu linkers rust-lang#73384 * Disable the `SimplifyArmIdentity` pass rust-lang#73262 * Allow inference regions when relating consts rust-lang#73225 * Fix link error with #[thread_local] introduced by rust-lang#71192 rust-lang#73065 * Ensure stack when building MIR for matches rust-lang#72941 * Don't create impl candidates when obligation contains errors rust-lang#73005 r? @ghost
This pass is buggy so I'm disabling it to fix a stable-to-beta
regression.
Related to #73223