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Simplify some code that depend on Deref#97077

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ouz-a:Optimize-backend
Jul 26, 2022
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Simplify some code that depend on Deref#97077
bors merged 4 commits intorust-lang:masterfrom
ouz-a:Optimize-backend

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@ouz-a ouz-a commented May 16, 2022

Now that we can assume #97025 works, it's safe to expect Deref is always in the first place of projections. With this, I was able to simplify some code that depended on Deref's place in projections. When we are able to move Derefer before ElaborateDrops successfully we will be able to optimize more places.

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@rustbot rustbot added the T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. label May 16, 2022
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bors commented May 22, 2022

☔ The latest upstream changes (presumably #97265) made this pull request unmergeable. Please resolve the merge conflicts.

@ouz-a ouz-a force-pushed the Optimize-backend branch from 2cd4c78 to a28553a Compare May 31, 2022 09:04
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@oli-obk oli-obk added the S-blocked Status: Blocked on something else such as an RFC or other implementation work. label Jun 2, 2022
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oli-obk commented Jun 2, 2022

Blocked on #95576

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bors commented Jun 21, 2022

☔ The latest upstream changes (presumably #95576) made this pull request unmergeable. Please resolve the merge conflicts.

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pnkfelix commented Jul 21, 2022

@rustbot label: -S-blocked +S-waiting-on-author

@rustbot rustbot added S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. and removed S-blocked Status: Blocked on something else such as an RFC or other implementation work. labels Jul 21, 2022
@ouz-a ouz-a force-pushed the Optimize-backend branch from a28553a to 447aace Compare July 22, 2022 16:24
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rustbot commented Jul 22, 2022

Some changes occurred to MIR optimizations

cc @rust-lang/wg-mir-opt

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oli-obk commented Jul 25, 2022

@bors r+

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bors commented Jul 25, 2022

📌 Commit 9f00d83 has been approved by oli-obk

It is now in the queue for this repository.

@bors bors removed the S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. label Jul 25, 2022
@bors bors added S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. and removed S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. labels Jul 25, 2022
@JohnTitor JohnTitor mentioned this pull request Jul 25, 2022
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bors added a commit to rust-lang-ci/rust that referenced this pull request Jul 25, 2022
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Auto merge of rust-lang#99735 - JohnTitor:rollup-d93jyr2, r=JohnTitor
a867059 
Rollup of 9 pull requests

Successful merges:

 - rust-lang#92390 (Constify a few `(Partial)Ord` impls)
 - rust-lang#97077 (Simplify some code that depend on Deref)
 - rust-lang#98710 (correct the output of a `capacity` method example)
 - rust-lang#99084 (clarify how write_bytes can lead to UB due to invalid values)
 - rust-lang#99178 (Lighten up const_prop_lint, reusing const_prop)
 - rust-lang#99673 (don't ICE on invalid dyn calls)
 - rust-lang#99703 (Expose size_hint() for TokenStream's iterator)
 - rust-lang#99709 (`Inherited` always has `TypeckResults` available)
 - rust-lang#99713 (Fix sidebar background)

Failed merges:

r? `@ghost`
`@rustbot` modify labels: rollup
@bors bors merged commit 2989275 into rust-lang:master Jul 26, 2022
@rustbot rustbot added this to the 1.64.0 milestone Jul 26, 2022
@ouz-a ouz-a deleted the Optimize-backend branch November 13, 2022 09:55
RalfJung
RalfJung reviewed Aug 3, 2023
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compiler/rustc_middle/src/mir/mod.rs

/// If MirPhase >= Derefered and if projection contains Deref,
/// It's guaranteed to be in the first place
pub fn has_deref(&self) -> bool {
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This is super confusing, we now have is_indirect and has_deref and they are basically checking the same thing except one assumes we are in a certain MIR phase and the other doesn't. These doc comments of both methods should explain when to use one vs the other.

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@ouz-a ouz-a Aug 5, 2023

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I wrote this function, I don't quite remember the details why we needed to check if Deref was in first place or not but I remember it making quite big difference.

RalfJung
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compiler/rustc_middle/src/mir/mod.rs
/// If MirPhase >= Derefered and if projection contains Deref,
/// It's guaranteed to be in the first place
pub fn has_deref(&self) -> bool {
self.projection.first() == Some(&PlaceElem::Deref)
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@RalfJung RalfJung Aug 3, 2023 •
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The same debug assertion should also be added here -- right now it seems very easy to accidentally call has_deref before the "deref only in first projection" invariant has been established, and then we'll get the weirdest bugs.

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Added the debug assertion and bit better documentation here #114505

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