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gccrs:fix ICE with continue/break/return in while condition #4270

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@Harishankar14 Harishankar14 commented Nov 6, 2025

Fixes ICE when continue/break/return/loop are used as while conditions. The compiler now emits a proper error message instead of crashing.

Fixes #3977

Thank you for making Rust GCC better!

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@Harishankar14 Harishankar14 changed the title Fix ICE with continue/break/return in while condition,Fixes #3977 gccrs:Fix ICE with continue/break/return in while condition,Fixes #3977 Nov 6, 2025
@Harishankar14 Harishankar14 force-pushed the fold-convert branch 2 times, most recently from 2f08a77 to 6e26f4c Compare November 7, 2025 06:19
@Harishankar14 Harishankar14 changed the title gccrs:Fix ICE with continue/break/return in while condition,Fixes #3977 gccrs:fix ICE with continue/break/return in while condition,fixes #3977 Nov 7, 2025
@Harishankar14 Harishankar14 changed the title gccrs:fix ICE with continue/break/return in while condition,fixes #3977 gccrs:fix ICE with continue/break/return in while condition Nov 7, 2025
@Harishankar14 Harishankar14 force-pushed the fold-convert branch 3 times, most recently from ea6ad41 to bd1e92a Compare November 7, 2025 07:20
@Harishankar14 Harishankar14 marked this pull request as draft November 7, 2025 08:28
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powerboat9 commented Nov 8, 2025

https://play.rust-lang.org/?version=stable&mode=debug&edition=2024&gist=f4db2628116a78ca94e09a3cf1bcfb21

Having a predicate of type ! should work -- it gets coerced into a boolean. See https://doc.rust-lang.org/reference/types/never.html, though don't get confused by the last paragraph

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Harishankar14 commented Nov 9, 2025

@powerboat9 Thanks for the feedback! I dont really know how did i miss this.. I've updated the fix to properly handle never-type coercion. Instead of rejecting continue as a value, the compiler now:

Detects when the while predicate has type ! (never)
Coerces it to bool by treating it as true (infinite loop)
Issues a warning about unreachable code

@Harishankar14 Harishankar14 marked this pull request as ready for review November 9, 2025 21:26
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Harishankar14 commented Nov 9, 2025

@powerboat9, @philberty

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i think this can be simplified a fair bit but good job.

@Harishankar14 Harishankar14 force-pushed the fold-convert branch 2 times, most recently from 58fd25a to 9daabe7 Compare November 10, 2025 08:11
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Harishankar14 commented Nov 11, 2025

@philberty LMK, if any changes required. Applied all the ones which you pointed out. :)

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Harishankar14 commented Nov 13, 2025

https://play.rust-lang.org/?version=stable&mode=debug&edition=2024&gist=f4db2628116a78ca94e09a3cf1bcfb21

Having a predicate of type ! should work -- it gets coerced into a boolean. See https://doc.rust-lang.org/reference/types/never.html, though don't get confused by the last paragraph

@powerboat9 This should do, lmk your thoughts.

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@Harishankar14 Harishankar14 marked this pull request as draft November 15, 2025 11:09
@Harishankar14 Harishankar14 marked this pull request as ready for review November 15, 2025 12:04
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@Harishankar14 Harishankar14 force-pushed the fold-convert branch 2 times, most recently from 0007616 to e14f017 Compare November 17, 2025 19:33
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nearly there

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Harishankar14 commented Nov 20, 2025

nearly there

Yeah completed as per your suggestions,waiting for your review @philberty

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philberty commented Nov 24, 2025

you need to fix the commit format CI is failing for you.

@Harishankar14
Fix ICE with continue/break/return in while condition
c218485 
Fixes Rust-GCC#3977

The predicate expression must be evaluated before type checking
to ensure side effects occur even when the predicate has never type.
This prevents skipping function calls, panics, or other side effects
in diverging predicates.

gcc/rust/ChangeLog:

	* backend/rust-compile-expr.cc (CompileExpr::visit): Always
	evaluate predicate expression before checking for never type
	to preserve side effects in while loop conditions.
	* typecheck/rust-hir-type-check-expr.cc: Update handling of break/continue.

gcc/testsuite/ChangeLog:

	* rust/compile/issue-3977.rs: New test.

Signed-off-by: Harishankar <harishankarpp7@gmail.com>
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Harishankar14 commented Nov 24, 2025 •
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you need to fix the commit format CI is failing for you.

Yep, done @philberty

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yeah that condition isnt correct you still need to make the loop evaluate the expression you should be using -fdump-tree-gimple to verify the logic

gcc/rust/backend/rust-compile-expr.cc
if (predicate_type->get_kind () == TyTy::TypeKind::NEVER)
{
ctx->add_statement (condition);
condition = boolean_true_node;
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i dont think this is right to just override to boolean_true_node it means the never expression will never get evaluated

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I think ctx->add_statement takes care of that

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ICE in fold_convert_loc, at fold-const.cc:2662

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