coverage: Avoid overflow when the MC/DC condition limit is exceeded #125700
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r? @nnethercote rustbot has assigned @nnethercote. Use |
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| @@ -217,7 +217,7 @@ impl MCDCInfoBuilder { | |||
| } | |||
| _ => { | |||
| // Do not generate mcdc mappings and statements for decisions with too many conditions. | |||
| let rebase_idx = self.branch_spans.len() - decision.conditions_num + 1; | |||
| let rebase_idx = self.branch_spans.len() + 1 - decision.conditions_num; | |||
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A comment about the ordering here seems warranted.
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After considering what to write for the comment, I noticed that in context this would be better off subtracting 1 from the RHS instead.
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r=me with the comments added. @bors delegate=Zalathar |
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✌️ @Zalathar, you can now approve this pull request! If @nnethercote told you to " |
If we perform this subtraction and then add 1, the subtraction can sometimes overflow to -1 before the addition can bring its value back to 0. That behaviour seems to be benign, but it nevertheless causes test failures in compiler configurations that check for overflow. We can avoid the overflow by instead subtracting (N - 1), which is algebraically equivalent, and more closely matches what the code is actually trying to do.
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@nnethercote I ended up changing the code in a small but significant way (diff), which is a bit of a grey area for the delegated approval, so I'm going to err on the side of caution and not just enqueue it immediately. |
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👍 @bors r+ |
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…cote coverage: Avoid overflow when the MC/DC condition limit is exceeded Fix for the test failure seen in rust-lang#124571 (comment). If we perform this subtraction first, it can sometimes overflow to -1 before the addition can bring its value back to 0. That behaviour seems to be benign, but it nevertheless causes test failures in compiler configurations that check for overflow. `@rustbot` label +A-code-coverage
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…iaskrgr Rollup of 6 pull requests Successful merges: - rust-lang#107099 (rustdoc: Add support for --remap-path-prefix) - rust-lang#125693 (Format all source files in `tests/coverage/`) - rust-lang#125700 (coverage: Avoid overflow when the MC/DC condition limit is exceeded) - rust-lang#125705 (Reintroduce name resolution check for trying to access locals from an inline const) - rust-lang#125708 (tier 3 target policy: clarify the point about producing assembly) - rust-lang#125715 (remove unneeded extern crate in rmake test) r? `@ghost` `@rustbot` modify labels: rollup
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…iaskrgr Rollup of 7 pull requests Successful merges: - rust-lang#124655 (Add `-Zfixed-x18`) - rust-lang#125693 (Format all source files in `tests/coverage/`) - rust-lang#125700 (coverage: Avoid overflow when the MC/DC condition limit is exceeded) - rust-lang#125705 (Reintroduce name resolution check for trying to access locals from an inline const) - rust-lang#125708 (tier 3 target policy: clarify the point about producing assembly) - rust-lang#125715 (remove unneeded extern crate in rmake test) - rust-lang#125719 (Extract coverage-specific code out of `compiletest::runtest`) r? `@ghost` `@rustbot` modify labels: rollup
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Rollup merge of rust-lang#125700 - Zalathar:limit-overflow, r=nnethercote coverage: Avoid overflow when the MC/DC condition limit is exceeded Fix for the test failure seen in rust-lang#124571 (comment). If we perform this subtraction first, it can sometimes overflow to -1 before the addition can bring its value back to 0. That behaviour seems to be benign, but it nevertheless causes test failures in compiler configurations that check for overflow. ``@rustbot`` label +A-code-coverage
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coverage: Rename MC/DC `conditions_num` to `num_conditions` Updated version of rust-lang#124571, without the other changes that were split out into rust-lang#125108 and rust-lang#125700. This value represents a quantity of conditions, not an ID, so the new spelling is more appropriate. Some of the code touched by this PR could perhaps use some other changes, but I would prefer to keep this PR as a simple renaming and avoid scope creep. `@rustbot` label +A-code-coverage
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Rollup merge of rust-lang#125754 - Zalathar:conditions-num, r=lqd coverage: Rename MC/DC `conditions_num` to `num_conditions` Updated version of rust-lang#124571, without the other changes that were split out into rust-lang#125108 and rust-lang#125700. This value represents a quantity of conditions, not an ID, so the new spelling is more appropriate. Some of the code touched by this PR could perhaps use some other changes, but I would prefer to keep this PR as a simple renaming and avoid scope creep. `@rustbot` label +A-code-coverage
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Fix for the test failure seen in #124571 (comment).
If we perform this subtraction first, it can sometimes overflow to -1 before the addition can bring its value back to 0.
That behaviour seems to be benign, but it nevertheless causes test failures in compiler configurations that check for overflow.
@rustbot label +A-code-coverage