Improve resolution and compilation of control flow loops and labels by Islam-Imad · Pull Request #4522 · Rust-GCC/gccrs

Islam-Imad · 2026-04-12T17:33:49Z

This patch fixes and improves the handling of loop expressions, particularly
focusing on break and continue statements within labeled and nested loops.
closes #4521
closes #4530

Islam-Imad · 2026-04-12T17:35:35Z

cc @powerboat9

powerboat9 · 2026-04-12T21:08:53Z

+        res += i;
+        i += 1;
+        if res + i >= 99 {
+            break 'calculation;


Does continue 'calculation work?

i don't think because the label now after the loop.
i will check it then ping u for review

its impossible to create a single label for both continue and break. we have to create two labels one at the start and one at the end. right now i am hacking gcc/go to see how this problem is solved and yeah there is separation.

this will require more work to be done since we need to modify [loop,while,continue,break] and a lot of testing also. once its ready i will make it open again.

Islam-Imad · 2026-04-19T20:27:02Z

@powerboat9 this is the core part of the patch, it still not ready.
i will add more tests, refactor again and remove the debugs.
i will continue explaining the changes in this document also link.
i hope tommorrow to submit the final patch.
also i am not sure about my solution to loop resolve problem.

Islam-Imad · 2026-04-23T10:02:15Z

ping ?

powerboat9 · 2026-04-26T16:03:06Z

Could you squash the commits?

Islam-Imad · 2026-04-26T17:11:32Z

ok i will but i am asking if there something i should i update or not ?

Islam-Imad · 2026-04-26T17:28:05Z

Could you squash the commits?

done :)

Islam-Imad · 2026-04-28T11:51:18Z

ping ?

Islam-Imad · 2026-05-23T05:24:53Z

is there any feedback on this ?

P-E-P · 2026-05-24T14:16:52Z

+    compiled_break_labels[id] = label;
+  }
+
+  bool lookup_break_label (HirId id, tree *label)


Even if the old API uses an out pointer with a bool return value most of the new APIs try to use optional when available.

Even if the old API uses an out pointer with a bool return value most of the new APIs try to use optional when available.

i suggest to open a new PR to refactor the old APIs. what do u think ?

yes that would be a good idea :) do you want to work on that?

yes just mention this comment in an issue and assign it to me.

P-E-P · 2026-05-24T14:20:33Z

+    compiled_continue_labels[id] = label;
+  }
+
+  bool lookup_continue_label (HirId id, tree *label)


Islam-Imad · 2026-07-06T07:13:47Z

CC @P-E-P @powerboat9

dkm · 2026-07-06T09:36:03Z

Drive-by comment on changelog... Looks like the first entry is not correct:

	* backend/rust-compile-context.h: Push, Pop, Peek different labels.

As you're adding a bunch of new functions, I think there should be entries like:

	* backend/rust-compile-context.h (bla): New function.

What do you think?

Islam-Imad · 2026-07-06T11:46:39Z

Drive-by comment on changelog... Looks like the first entry is not correct:
	* backend/rust-compile-context.h: Push, Pop, Peek different labels.
As you're adding a bunch of new functions, I think there should be entries like:
	* backend/rust-compile-context.h (bla): New function.
What do you think?

I have used the mklog script :) , i have added entries for the new functions manually.
also updated the changes log to be more clear.

CohenArthur · 2026-07-08T09:15:17Z

+
+  tree pop_loop_end_label ()
+  {
+    tree pop = loop_end_labels.back ();


This is undefined behavior if the vector is empty. Add an assertion that it isn't like you did in peek_loop_end_label

CohenArthur · 2026-07-08T09:16:14Z

  std::vector<::std::vector<DropCandidate>> block_drop_candidates;
  std::vector<::Bvariable *> loop_value_stack;
  std::vector<tree> loop_begin_labels;
+  std::vector<tree> loop_end_labels;


Would it make sense to use something like the StackedContexts<T> class here?

i think yes but i prefer to open a new refactor PR for compilation-context to make use of it and also update the old APIs.

CohenArthur · 2026-07-08T09:20:26Z

-	loop_label.get_lifetime ().get_mappings ().get_hirid (), label);
-      // Associate the loop's result temporary with the label so that a
-      // `break 'label value` can locate it (see visit (HIR::BreakExpr)).
+      loop_label = tl::optional<HIR::LoopLabel> (expr.get_loop_label ());


You don't need the constructor here

Suggested change

loop_label = tl::optional<HIR::LoopLabel> (expr.get_loop_label ());

loop_label = expr.get_loop_label ();

Islam-Imad · 2026-07-12T08:35:19Z

ci failure ? but its ok on my machine

powerboat9 · 2026-07-12T14:24:07Z

Looks like it's either a gcc5 specific issue, or some undefined behavior is semi-randomly causing problems. Maybe try running with valgrind?

Islam-Imad · 2026-07-13T06:12:39Z

@powerboat9 i just rerun the CI again and its now green.

P-E-P · 2026-07-13T23:19:36Z

+            'high: loop {
+                dump_number(3);
+                break 'mid;
+                dump_number(3);


I would dump another number here to explicitly tell the user were something has gone wrong when the compiler breaks.

P-E-P · 2026-07-13T23:19:51Z

+                break 'mid;
+                dump_number(3);
+            }
+            dump_number(2);


This batch fixes and improves the handling of loop expressions, particularly focusing on `break` and `continue` statements within labeled and nested loops. gcc/rust/ChangeLog: * backend/rust-compile-context.h (RUST_COMPILE_CONTEXT): loop labels context functions. - insert_break_label - lookup_break_label - insert_continue_label - lookup_continue_label - push/pop/peek end_label (similar to begin_label). * backend/rust-compile-expr.cc (CompileExpr::visit): handle loop labels construction in WhileExpr, ForExpr, ContinueExpr and BreakExpr. (CompileExpr::construct_block_label): construct break label instead of normal label to unify handling break statement. (CompileExpr::construct_loop_labels): construct while/for loops labels (continue label before loop, break label after loop). * backend/rust-compile-expr.h (RUST_COMPILE_EXPR): construct_loop_labels function header. * resolve/rust-default-resolver.cc (DefaultResolver::visit): Fix labels. * resolve/rust-default-resolver.h: Fix labels. * resolve/rust-name-resolution-context.cc (NameResolutionContext::insert): Fix labels. (NameResolutionContext::insert_shadowable): Fix labels. (NameResolutionContext::insert_globbed): Fix labels. (NameResolutionContext::scoped): Fix labels. gcc/testsuite/ChangeLog: * rust/execute/cf-break-continue.rs: New test. * rust/execute/cf-label-shadowing.rs: New test. * rust/execute/cf-labeled-break-nested.rs: New test. * rust/execute/cf-labeled-continue-nested.rs: New test. * rust/execute/cf-labeled-loops.rs: New test. * rust/execute/cf-loop-break-continue.rs: New test. * rust/execute/cf-mixed-labeled-unlabeled.rs: New test. * rust/execute/cf-nested-loops.rs: New test. Signed-off-by: Islam-Imad <islamimad404@gmail.com>

Islam-Imad · 2026-07-20T08:00:39Z

the test is updated @P-E-P

Islam-Imad · 2026-07-20T08:43:54Z

cc @powerboat9 @P-E-P

powerboat9 reviewed Apr 12, 2026

View reviewed changes

Islam-Imad marked this pull request as draft April 13, 2026 14:46

Islam-Imad force-pushed the fix/while-loop-label-break branch from dfc3c94 to d6e32c3 Compare April 19, 2026 20:22

Islam-Imad force-pushed the fix/while-loop-label-break branch 4 times, most recently from d3de692 to 75570ed Compare April 20, 2026 17:35

Islam-Imad marked this pull request as ready for review April 20, 2026 18:28

Islam-Imad requested a review from powerboat9 April 20, 2026 18:28

Islam-Imad changed the title ~~Fix loop label placement in WhileLoopExpr lowering~~ Improve resolution and compilation of control flow loops and labels Apr 20, 2026

Islam-Imad force-pushed the fix/while-loop-label-break branch from 75570ed to 426f0bb Compare April 26, 2026 17:18

P-E-P requested review from P-E-P and philberty April 30, 2026 14:03

P-E-P reviewed May 24, 2026

View reviewed changes

Islam-Imad force-pushed the fix/while-loop-label-break branch from 426f0bb to 7383411 Compare July 6, 2026 06:43

Islam-Imad force-pushed the fix/while-loop-label-break branch 2 times, most recently from 027469a to 35596f8 Compare July 6, 2026 11:38

Islam-Imad requested a review from P-E-P July 6, 2026 11:48

CohenArthur reviewed Jul 8, 2026

View reviewed changes

Islam-Imad force-pushed the fix/while-loop-label-break branch 2 times, most recently from b73ece7 to 7a55fac Compare July 12, 2026 07:29

Islam-Imad requested a review from CohenArthur July 12, 2026 07:30

Islam-Imad force-pushed the fix/while-loop-label-break branch from 7a55fac to c2a3c97 Compare July 13, 2026 05:32

P-E-P approved these changes Jul 14, 2026

View reviewed changes

Islam-Imad force-pushed the fix/while-loop-label-break branch from c2a3c97 to 886ef77 Compare July 20, 2026 07:42

Islam-Imad force-pushed the fix/while-loop-label-break branch from 886ef77 to 7399903 Compare July 20, 2026 07:47

P-E-P added this pull request to the merge queue Jul 20, 2026

Merged via the queue into Rust-GCC:master with commit bf3ef5f Jul 20, 2026
13 checks passed

	loop_label = tl::optional<HIR::LoopLabel> (expr.get_loop_label ());
	loop_label = expr.get_loop_label ();

Uh oh!

Conversation

Islam-Imad commented Apr 12, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Uh oh!

Islam-Imad commented Apr 12, 2026

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Islam-Imad commented Apr 19, 2026

Uh oh!

Islam-Imad commented Apr 23, 2026

Uh oh!

powerboat9 commented Apr 26, 2026

Uh oh!

Islam-Imad commented Apr 26, 2026

Uh oh!

Islam-Imad commented Apr 26, 2026

Uh oh!

Islam-Imad commented Apr 28, 2026

Uh oh!

Islam-Imad commented May 23, 2026

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Islam-Imad Jul 8, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Islam-Imad commented Jul 6, 2026

Uh oh!

dkm commented Jul 6, 2026

Uh oh!

Islam-Imad commented Jul 6, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Islam-Imad commented Jul 12, 2026

Uh oh!

powerboat9 commented Jul 12, 2026

Uh oh!

Islam-Imad commented Jul 13, 2026

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Islam-Imad commented Jul 20, 2026

Uh oh!

Islam-Imad commented Jul 20, 2026

Uh oh!

Uh oh!

Reviewers

Islam-Imad commented Apr 12, 2026 •

edited

Loading

Islam-Imad Jul 8, 2026 •

edited

Loading

Islam-Imad commented Jul 6, 2026 •

edited

Loading