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merged 1 commit into from
Oct 20, 2019
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Inline ptr::null(_mut) even in debug builds #64996

merged 1 commit into from
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tesuji
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@tesuji tesuji commented Oct 2, 2019 •
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I think we should treat ptr::null(_mut) as a constant. As It may help reduce code size
in debug build.
See godbolt link: https://godbolt.org/z/b9YMtD

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r? @Kimundi

(rust_highfive has picked a reviewer for you, use r? to override)

@rust-highfive rust-highfive added the S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. label Oct 2, 2019
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tesuji commented Oct 2, 2019

r? @eddyb

@rust-highfive rust-highfive assigned eddyb and unassigned Kimundi Oct 2, 2019
@tesuji tesuji closed this Oct 2, 2019
@tesuji tesuji reopened this Oct 2, 2019
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eddyb commented Oct 2, 2019

LGTM but I'm not sure what our inline policy is, cc @nagisa @rkruppe @gnzlbg

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nagisa commented Oct 2, 2019

I am amused that we do not "just" evaluate ptr::null, as it is a const fn with no arguments…

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nagisa commented Oct 2, 2019

IIRC if there is code that uses #[inline(always)] as opposed to #[inline] the backend automatically toggles opt-level=1, which is what ends up actually making the inline happen. No strong opposition against this change either way.

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hanna-kruppe commented Oct 2, 2019 •
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IIRC if there is code that uses #[inline(always)] as opposed to #[inline] the backend automatically toggles opt-level=1, which is what ends up actually making the inline happen. No strong opposition against this change either way.

That would surprise me a lot. I know for sure though that we run the AlwaysInline pass at -O0. This explains why the inlining happens and also why there is a pointless jump in the godbolt output (at -O1 that is cleaned up, presumably by SimplifyCFG).

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nagisa commented Oct 2, 2019

Eeh, my memory failed me then.

@tesuji tesuji mentioned this pull request Oct 2, 2019
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nagisa commented Oct 2, 2019

@oli-obk any ideas why const fns like these aren’t evaluated in-line? Should we do that?

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eddyb commented Oct 3, 2019

I think this would fit nicely into my recent suggestion to treat no-argument const fn as an opaque (i.e. we won't peek at the body) const.
(That was in the context of intrinsics like size_of but this seems similar)

Also, does the constant folding MIR pass handle const fn calls at all today?

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tesuji commented Oct 6, 2019

r? @oli-obk

@rust-highfive rust-highfive assigned oli-obk and unassigned eddyb Oct 6, 2019
@tesuji tesuji mentioned this pull request Oct 10, 2019
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Ping from triage
@oli-obk can you please review this pr?
cc: @nagisa @rkruppe @gnzlbg

thanks.

tmandry added a commit to tmandry/rust that referenced this pull request Oct 18, 2019
@tmandry
Rollup merge of rust-lang#65016 - lzutao:inline-mem-constfn, r=oli-obk
13e47c8 
Always inline `mem::{size_of,align_of}` in debug builds

Those two are const fn and do not have any arguments. Inlining
helps reducing generated code size in debug builds.

See also rust-lang#64996.
tmandry added a commit to tmandry/rust that referenced this pull request Oct 18, 2019
@tmandry
Rollup merge of rust-lang#65016 - lzutao:inline-mem-constfn, r=oli-obk
7167a59 
Always inline `mem::{size_of,align_of}` in debug builds

Those two are const fn and do not have any arguments. Inlining
helps reducing generated code size in debug builds.

See also rust-lang#64996.
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oli-obk commented Oct 19, 2019

@bors r+ rollup

Let's do this until const prop can handle function calls

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bors commented Oct 19, 2019

📌 Commit d0862ec has been approved by oli-obk

@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-review Status: Awaiting review from the assignee but also interested parties. labels Oct 19, 2019
Centril added a commit to Centril/rust that referenced this pull request Oct 19, 2019
@Centril
Rollup merge of rust-lang#64996 - lzutao:inline-ptr-null, r=oli-obk
4d96185 
Inline `ptr::null(_mut)` even in debug builds

I think we should treat `ptr::null(_mut)` as a constant. As It may help reduce code size
in debug build.
See godbolt link: https://godbolt.org/z/b9YMtD
@Centril Centril mentioned this pull request Oct 19, 2019
Closed
Centril added a commit to Centril/rust that referenced this pull request Oct 20, 2019
@Centril
Rollup merge of rust-lang#64996 - lzutao:inline-ptr-null, r=oli-obk
f01ffbc 
Inline `ptr::null(_mut)` even in debug builds

I think we should treat `ptr::null(_mut)` as a constant. As It may help reduce code size
in debug build.
See godbolt link: https://godbolt.org/z/b9YMtD
@Centril Centril mentioned this pull request Oct 20, 2019
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bors added a commit that referenced this pull request Oct 20, 2019
@bors
Auto merge of #65622 - Centril:rollup-l8orba7, r=Centril
89e645a 
Rollup of 6 pull requests

Successful merges:

 - #64996 (Inline `ptr::null(_mut)` even in debug builds)
 - #65551 (Avoid realloc in `CString::new`)
 - #65593 (add test for calling non-const fn)
 - #65595 (move `parse_cfgspecs` to `rustc_interface`)
 - #65600 (Remove unneeded `ref` from docs)
 - #65602 (Fix plural mistake in emitter.rs)

Failed merges:

r? @ghost
@bors bors merged commit d0862ec into rust-lang:master Oct 20, 2019
@tesuji tesuji deleted the inline-ptr-null branch October 20, 2019 18:10
@therealprof therealprof mentioned this pull request Oct 29, 2019
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@sinkuu sinkuu mentioned this pull request Oct 30, 2019
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@tesuji @rust-highfive @eddyb @nagisa @hanna-kruppe @JohnCSimon @oli-obk @bors @Kimundi