[MIR] Refine representation and translation of calls #30481

nagisa · 2015-12-19T14:58:53Z

This is a pretty big PR conflating changes to a few different block terminators (Call, DivergingCall, Panic, Resume, Diverge), because they are somewhat closely related.

Each commit has a pretty good description on what is being changed in each commit. The end result is greatly simplified CFG and translation for calls (no success branch if the function is diverging, no cleanup branch if there’s nothing to cleanup etc).

Fixes #30480
Fixes #29767
Partialy solves #29575
Fixes #29573

nagisa · 2015-12-19T15:32:19Z

src/librustc_trans/trans/mir/block.rs

+        match self.unreachable_block {
+            Some(b) => b,
+            None => {
+                let bl = self.bcx(mir::START_BLOCK).fcx.new_block(false, "unreachable", None);


Note to self: maybe self should contain a fcx too?

nagisa · 2015-12-21T20:31:10Z

All in all, I think it is in a good enough spot now to begin reviewing it @nikomatsakis.

luqmana · 2015-12-22T01:39:19Z

src/librustc_trans/trans/mir/block.rs

+                                      Some(attrs),
+                                      debugloc);
+                        if must_copy_dest {
+                            // FIXME: What do we do here?


AFAIK should just do the same as below: store_ty the result from Invoke to the destination.

The problem here (is much harder than it looks at the first look!) is that invoke is a basic block terminator and thus we cannot add anything else to the current block. We would have to add, or rather, prepend a store instruction to a success branch, but… that’s tricky, because:

That’s hacky (duh);

I can’t seem to see anyway to do it;

It would make some already-generated blocks invalid (e.g. we would have to assert that success branch has higher basic-block number and has not been translated yet).

Basically, to me it seems like we should change the MIR some more and figure out if destination must be copied (or rather, avoid copying destination altogether as well as encoding the copy, if necessary) during the MIR build phase.

EDIT: we could also generate a temporary block with a store and branch to success block in it (still doesn’t avoid 3rd issue). Sounds like a most correct hack to do, but I’ll see if anybody has better ideas.

nikomatsakis · 2015-12-22T10:38:58Z

As I mentioned on IRC, I'm not sure if I think that splitting out "diverging call" into its own terminator is a good idea. My concerns are:

Duplication: it's harder to know that you're getting all calls.
If you have foo = diverging_fn(), we need to still consider that a "write" to foo in a logical sense (i.e., for the purposes of borrowck). To do that under the approach of this PR, we'll need some marker that foo has been initialized, since DivergingCall no longer has a destination.

Basically, I'm not sure if the code for handling calls vs diverging calls will wind up being so very different in other passes. But it's a bit hard to know just now. A compromise might just be to introduce an enum into the call that is either NormalCall(BasicBlock, BasicBlock) or DivergingCall(BasicBlock).

In any case, let me read further before reaching final judgement.

nagisa · 2015-12-22T11:19:20Z

As I mentioned on IRC, I'm not sure if I think that splitting out "diverging call" into its own terminator is a good idea. My concerns are:

The last commit contains conversion to inner-enum, like you proposed on IRC. Feel free to compare.

nagisa · 2015-12-22T15:28:05Z

Comments on nagisa@0c7d57d are yet to be fixed.

EDIT: changed/fixed in nagisa@1c2f0d8. @nikomatsakis the code still looks equally ugly to me, but not sure if it could be made any better.

bors · 2016-01-04T07:48:01Z

☔ The latest upstream changes (presumably #30651) made this pull request unmergeable. Please resolve the merge conflicts.

nikomatsakis · 2016-01-04T19:29:18Z

In all those cases where I gave nits about exhaustive matches, we were just trying to handle converging cases -- might be that a helper function for extracting the converging cases would be good. OTOH, I guess this is why you split those cases into two to start with.

nikomatsakis · 2016-01-04T19:53:19Z

OK, so, as you say, this is a big PR, and I feel like I could go on pointing out nits forever. But I'd rather we land it and just hack and try to clean things up. Some of these commits get pretty involved, but that may just be unavoidable if we want to generate less naive IR. Calls are just complicated. :) Anyway, so I'm leaning now towards landing this PR and then trying to keep improving things. One thing which would be nice are some more test cases for calls that generate invoke, and in particular to exercise some of those edge cases paths (like loop { c = call(); }).

bors · 2016-01-04T22:12:29Z

☔ The latest upstream changes (presumably #30602) made this pull request unmergeable. Please resolve the merge conflicts.

nagisa · 2016-01-05T14:56:55Z

@nikomatsakis rebased and comments addressed (I hope I didn’t miss any). I added a few more tests as well.

nikomatsakis · 2016-01-05T16:02:50Z

r=me modulo final nits (in particular, the test with graphviz attribute should really be fixed)

bors · 2016-01-06T01:55:44Z

💔 Test failed - auto-win-msvc-64-opt

bors · 2016-01-06T07:31:27Z

☔ The latest upstream changes (presumably #30492) made this pull request unmergeable. Please resolve the merge conflicts.

DivergingCall is different enough from the regular converging Call to warrant the split. This also inlines CallData struct and creates a new CallTargets enum in order to have a way to differentiate between calls that do not have an associated cleanup block. Note, that this patch still does not produce DivergingCall terminator anywhere. Look for that in the next patches.

This simplifies CFG greatly for some cases :)

Diverge should eventually go away

Unreachable terminator can be contained all within the trans.

It is useful for various cases where direct unreachable cannot be translated and a separate block is necessary.

* Implement landing pads; and * Implement DivergingCall translation; and * Modernise previous implementation of Call somewhat.

Fixes rust-lang#30480

This merges two separate Call terminators and uses a separate CallKind sub-enum instead. A little bit unrelatedly, copying into destination value for a certain kind of invoke, is also implemented here. See the associated comment in code for various details that arise with this implementation.

Not any more beautiful.

This considerably simplifies code around calling functions and translation of Resume itself. This removes requirement that a block containing Resume terminator is always translated after something which creates a landing pad, thus allowing us to actually translate some valid MIRs we could not translate before. However, an assumption is added that translator is correct (in regards to landing pad generation) and code will never reach the Resume terminator without going through a landing pad first. Breaking these assumptions would pass an `undef` value into the personality functions.

Manishearth · 2016-01-06T11:59:00Z

@bors r=nikomatsakis

bors · 2016-01-06T11:59:01Z

📌 Commit 36b3951 has been approved by nikomatsakis

bors · 2016-01-06T13:11:19Z

⌛ Testing commit 36b3951 with merge d5ac1a1...

@nikomatsakis

r? @nikomatsakis This is a pretty big PR conflating changes to a few different block terminators (Call, DivergingCall, Panic, Resume, Diverge), because they are somewhat closely related. Each commit has a pretty good description on what is being changed in each commit. The end result is greatly simplified CFG and translation for calls (no success branch if the function is diverging, no cleanup branch if there’s nothing to cleanup etc). Fixes #30480 Fixes #29767 Partialy solves #29575 Fixes #29573

bors · 2016-01-06T15:00:15Z

☀️ Test successful - auto-linux-32-nopt-t, auto-linux-32-opt, auto-linux-64-debug-opt, auto-linux-64-nopt-t, auto-linux-64-opt, auto-linux-64-x-android-t, auto-linux-cross-opt, auto-linux-musl-64-opt, auto-mac-32-opt, auto-mac-64-nopt-t, auto-mac-64-opt, auto-win-gnu-32-nopt-t, auto-win-gnu-32-opt, auto-win-gnu-64-nopt-t, auto-win-gnu-64-opt, auto-win-msvc-32-opt, auto-win-msvc-64-opt

solson · 2016-01-07T02:27:52Z

src/librustc/mir/repr.rs

+    pub fn destination(&self) -> Option<Lvalue<'tcx>> {
+        match *self {
+            CallKind::Converging { ref destination, .. } |
+            CallKind::ConvergingCleanup { ref destination, .. } => Some(destination.clone()),


Why clone here instead of returning Option<&Lvalue<'tcx>> and letting the caller decide if it needs to clone?

There’s two reasons, mostly, I had in mind:

Cloning Lvalue is very cheap most of the time (i.e. when Lvalue is not a Projection);

There’s users who want &mut lvalue and there’s users who want &lvalue. Returning a value allows to make either one easier when pattern matching (ref vs ref mut).

On the hindsight, I think this might actually be a bug to return destination by value in some cases which I didn’t think about before, thus I’ll submit a patch in a moment making these return a mutable reference instead.

@nagisa

This just removes the `Some()` that appeared around terminators in MIR text output after #30481 (cc @nagisa). The graphviz is already fixed. r? @eddyb

@nagisa

This just removes the `Some()` that appeared around terminators in MIR text output after rust-lang#30481 (cc @nagisa). The graphviz is already fixed. r? @eddyb

@nagisa

This just removes the `Some()` that appeared around terminators in MIR text output after rust-lang#30481 (cc @nagisa). The graphviz is already fixed. r? @eddyb

rust-highfive assigned nikomatsakis Dec 19, 2015

nagisa reviewed Dec 19, 2015
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nagisa force-pushed the mir-calls-2 branch from ffebbf1 to acc49ad Compare December 19, 2015 15:43

nagisa changed the title ~~Refine representation and translation of MIR calls~~ [MIR] Refine representation and translation of calls Dec 19, 2015

nagisa force-pushed the mir-calls-2 branch 3 times, most recently from 0f066dc to fdaa56a Compare December 21, 2015 19:58

nagisa force-pushed the mir-calls-2 branch from b245183 to fdaa56a Compare December 21, 2015 22:16

luqmana reviewed Dec 22, 2015
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luqmana mentioned this pull request Dec 22, 2015

[MIR] Calling extern functions. #30517

Closed

nagisa force-pushed the mir-calls-2 branch from 6227ccc to b0832b8 Compare December 22, 2015 15:27

nagisa force-pushed the mir-calls-2 branch from 1c2f0d8 to 3c05a45 Compare January 1, 2016 22:54

nagisa force-pushed the mir-calls-2 branch from 3c05a45 to f6d2faf Compare January 4, 2016 16:11

nagisa force-pushed the mir-calls-2 branch 3 times, most recently from e482e81 to d468ec9 Compare January 5, 2016 00:42

nagisa force-pushed the mir-calls-2 branch 2 times, most recently from 2e9e015 to 9e7ffb6 Compare January 5, 2016 15:18

nagisa force-pushed the mir-calls-2 branch from 9e7ffb6 to 559c9c5 Compare January 5, 2016 18:58

nagisa added 13 commits January 6, 2016 13:40

Generate DivergingCall terminator

6f18b55

This simplifies CFG greatly for some cases :)

Add Resume Terminator which corresponds to resume

ecf4d0e

Diverge should eventually go away

Remove the Panic block terminator

5b34690

Remove diverge terminator

4e86dcd

Unreachable terminator can be contained all within the trans.

Have a cached unreachable block inside MIR state

a1e1398

It is useful for various cases where direct unreachable cannot be translated and a separate block is necessary.

Refine call terminator translation

924bb1e

* Implement landing pads; and * Implement DivergingCall translation; and * Modernise previous implementation of Call somewhat.

Fix ReturnPointer generation for void return types

20ec53a

Fixes rust-lang#30480

Don’t generate landing-pads if -Z no-landing-pads

cef6aee

Add tests

5010703

panic/panic_bounds_check to destructure tys

f981424

Not any more beautiful.

nagisa force-pushed the mir-calls-2 branch from 559c9c5 to 36b3951 Compare January 6, 2016 11:58

bors merged commit 36b3951 into rust-lang:master Jan 6, 2016

This was referenced Jan 6, 2016

[MIR] Enhance the SimplifyCfg pass to merge consecutive blocks #30238

Closed

[MIR] Generalize the depth first search logic and use it in all of SimplifyCfg. #30239

Closed

Implement unwinding for i686 MSVC #30448

Merged

solson reviewed Jan 7, 2016
View reviewed changes

solson mentioned this pull request Jan 7, 2016

Fix MIR text output for terminators since they were wrapped in Option. #30771

Merged

bors added a commit that referenced this pull request Jan 8, 2016

Auto merge of #30771 - tsion:mir-text-terminator-fix, r=eddyb

01c86ea

This just removes the `Some()` that appeared around terminators in MIR text output after #30481 (cc @nagisa). The graphviz is already fixed. r? @eddyb

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[MIR] Refine representation and translation of calls #30481

[MIR] Refine representation and translation of calls #30481

nagisa commented Dec 19, 2015

nagisa Dec 19, 2015

nagisa commented Dec 21, 2015

luqmana Dec 22, 2015

nagisa Dec 22, 2015

nikomatsakis commented Dec 22, 2015

nagisa commented Dec 22, 2015

nagisa commented Dec 22, 2015

bors commented Jan 4, 2016

nikomatsakis commented Jan 4, 2016

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nagisa commented Jan 5, 2016

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bors commented Jan 6, 2016

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Manishearth commented Jan 6, 2016

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solson Jan 7, 2016

nagisa Jan 7, 2016

[MIR] Refine representation and translation of calls #30481

[MIR] Refine representation and translation of calls #30481

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