math/big: test aliasing of Int.GCD's three results - #81239
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checkAliasingTwoResults spells out by hand the ways in which a method's two results can alias its arguments. That does not extend to GCD, which writes three results, z, x and y: two of them can alias two different arguments at the same time, and the combinations are no longer practical to enumerate by hand. Add checkAliasingResults, which takes the number of results and tries every assignment of results to arguments, and register GCD under GCD-ZXY. The new subtest has teeth. Changing GCD's zero fast path to read b.abs after z may already have overwritten it, instead of using the lenB snapshot, fails GCD-ZXY while the existing GCD, GCD-X and GCD-Y subtests all still pass.
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This PR (HEAD: 3b0db6e) has been imported to Gerrit for code review. Please visit Gerrit at https://go-review.googlesource.com/c/go/+/824585. Important tips:
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Message from Gopher Robot: Patch Set 1: (1 comment) Please don’t reply on this GitHub thread. Visit golang.org/cl/824585. |
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checkAliasingTwoResults spells out by hand the ways in which a method's two
results can alias its arguments. That does not extend to GCD, which writes
three results, z, x and y: two of them can alias two different arguments at
the same time, and the combinations are no longer practical to enumerate by
hand.
Add checkAliasingResults, which takes the number of results and tries every
assignment of results to arguments, and register GCD under GCD-ZXY.
The new subtest has teeth. Changing GCD's zero fast path to read b.abs after
z may already have overwritten it, instead of using the lenB snapshot, fails
GCD-ZXY while the existing GCD, GCD-X and GCD-Y subtests all still pass.