add #[rustc_layout(debug)]#69901

RalfJung · 2020-03-10T21:31:42Z

@eddyb recently told me about the #[rustc_layout] attribute, and I think it would be very useful if it could be used to print all the layout information Rust has about a type. When working with layouts (e.g. in Miri), it is often not clear how certain surface language features get represented internally. I have some awful hacks locally to be able to dump this debug information; with this attribute I could get it on the playground which is so much better. :)

rust-highfive · 2020-03-10T21:31:46Z

r? @cramertj

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jonas-schievink · 2020-03-10T21:35:15Z

Cool! This will be helpful for testing generator layout optimizations in the future.

RalfJung · 2020-03-10T21:45:40Z

I figured it would be useful for tons of stuff. :) We have to think of some ways to make sure that the right people even know about it... like finding a good place in the rustc dev guide to mention it. I also plan to write a blog post.

src/test/ui/layout/debug.rs

eddyb · 2020-03-10T21:57:44Z

cc @rust-lang/compiler

cramertj · 2020-03-10T22:10:38Z

r? @eddyb

RalfJung · 2020-03-20T16:48:48Z

@eddyb I made this work on type definitions, not just type aliases.

eddyb · 2020-03-20T18:28:51Z

@bors r+ Thanks!

bors · 2020-03-20T18:28:52Z

📌 Commit c62e36b has been approved by eddyb

eddyb · 2020-03-20T18:44:31Z

@bors r- (failed because formatting)

RalfJung · 2020-03-20T22:27:10Z

Fixed that.

@bors r=eddyb

bors · 2020-03-20T22:27:11Z

📌 Commit 7b49678 has been approved by eddyb

@eddyb

add #[rustc_layout(debug)] @eddyb recently told me about the `#[rustc_layout]` attribute, and I think it would be very useful if it could be used to print all the layout information Rust has about a type. When working with layouts (e.g. in Miri), it is often not clear how certain surface language features get represented internally. I have some awful hacks locally to be able to dump this debug information; with this attribute I could get it on the playground which is so much better. :)

@eddyb

add #[rustc_layout(debug)] @eddyb recently told me about the `#[rustc_layout]` attribute, and I think it would be very useful if it could be used to print all the layout information Rust has about a type. When working with layouts (e.g. in Miri), it is often not clear how certain surface language features get represented internally. I have some awful hacks locally to be able to dump this debug information; with this attribute I could get it on the playground which is so much better. :)

Centril · 2020-03-21T04:31:05Z

Failed in #70203 (comment), @bors r-

RalfJung · 2020-03-21T07:43:41Z

Looks like "preferred alignment" differs for some platforms:

---- [ui] ui/layout/debug.rs stdout ----
diff of stderr:

37	                        pow2: 0,
189	        },
190	        pref: Align {
-	            pow2: 3,
+	            pow2: 2,
192	        },
193	    },
194	    size: Size {

245	                        pow2: 2,
246	                    },
247	                    pref: Align {
-	                        pow2: 3,
+	                        pow2: 2,
249	                    },
250	                },
251	                size: Size {

275	                        pow2: 2,
276	                    },
277	                    pref: Align {
-	                        pow2: 3,
+	                        pow2: 2,
279	                    },
280	                },
281	                size: Size {

319	            pow2: 2,
320	        },
321	        pref: Align {
-	            pow2: 3,
+	            pow2: 2,
323	        },
324	    },
325	    size: Size {

@eddyb should I just normalize all pow2: [0-9]+ to pow2: $ALIGN to skip this problems?

eddyb · 2020-03-21T07:55:02Z

@RalfJung Does this work? pref: Align \{\n *pow2: [1-3],\n *\} to pref: $PREF_ALIGN.

RalfJung · 2020-03-21T09:11:28Z

Yes that works, nice.

@bors r=eddyb

bors · 2020-03-21T09:11:30Z

📌 Commit e548df7 has been approved by eddyb

@ghost

Rollup of 6 pull requests Successful merges: - rust-lang#69497 (Don't unwind when hitting the macro expansion recursion limit) - rust-lang#69901 (add #[rustc_layout(debug)]) - rust-lang#69910 (Avoid query type in generics) - rust-lang#69955 (Fix abort-on-eprintln during process shutdown) - rust-lang#70032 (put type params in front of const params in generics_of) - rust-lang#70119 (rustc: use LocalDefId instead of DefId in TypeckTables.) Failed merges: r? @ghost

elichai · 2020-04-06T21:02:49Z

That's awesome!
I was just looking for exactly that for C++ in the last few days :)

rust-highfive assigned cramertj Mar 10, 2020

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RalfJung force-pushed the rustc_layout branch from f4ce9bf to fffd89a Compare March 10, 2020 21:47

eddyb reviewed Mar 10, 2020

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RalfJung added 4 commits March 20, 2020 17:25

fix layout_test visitor name

0296d49

add debug option to #[rustc_layout]

55c2cf2

add a test for rustc_layout(debug)

d9f60bc

make rustc_layout also work for type definitions

c62e36b

RalfJung force-pushed the rustc_layout branch from fffd89a to c62e36b Compare March 20, 2020 16:48

eddyb approved these changes Mar 20, 2020

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fmt

7b49678

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Dylan-DPC-zz mentioned this pull request Mar 21, 2020

Rollup of 11 pull requests #70202

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Centril mentioned this pull request Mar 21, 2020

Rollup of 17 pull requests #70203

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normalize away preferred alignment

e548df7

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Dylan-DPC-zz mentioned this pull request Mar 21, 2020

Rollup of 6 pull requests #70222

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RalfJung mentioned this pull request Mar 23, 2020

Idea: guaranteed-zero padding for niches #70230

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memoryruins mentioned this pull request Mar 28, 2020

Async performance regression #70488

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