[PATCH] D121556: [randstruct] Add randomize structure layout support

[Bill Wendling via Phabricator via cfe-commits]

void added a comment.

In D121556#3445124 <https://reviews.llvm.org/D121556#3445124>, @aaron.ballman wrote:

> In D121556#3444837 <https://reviews.llvm.org/D121556#3444837>, @void wrote:
>
>> In D121556#3444434 <https://reviews.llvm.org/D121556#3444434>, @MaskRay wrote:
>>
>>> In D121556#3444260 <https://reviews.llvm.org/D121556#3444260>, @void wrote:
>>>
>>>> In D121556#3444221 <https://reviews.llvm.org/D121556#3444221>, @MaskRay wrote:
>>>>
>>>>> In D121556#3444131 <https://reviews.llvm.org/D121556#3444131>, @void wrote:
>>>>>
>>>>>> In D121556#3444021 <https://reviews.llvm.org/D121556#3444021>, @MaskRay wrote:
>>>>>>
>>>>>>> 7aa8c38a9e190aea14116028c38b1d9f54cbb0b3 <https://reviews.llvm.org/rG7aa8c38a9e190aea14116028c38b1d9f54cbb0b3> still uses `std::shuffle`, not incorporating the `llvm::shuffle` fixes I did.
>>>>>>
>>>>>> You said it was still failing after the std::shuffle to llvm::shuffle change.
>>>>>
>>>>> By saying it still failed, I meant there were other Windows vs non-Windows differences, not that std::shuffle=>llvm::shuffle was an unintended change.
>>>>
>>>> So does it work or not? If I change it to `llvm::shuffle`, will the tests fail or will they pass regardless of the platform?
>>>
>>> If you change `std::shuffle` to `llvm::shuffle` and  add back tests like `EXPECT_EQ(Expected, getFieldNamesFromRecord(RD));`, the test will likely fail on Windows.
>>> I recall that @aaron.ballman uses Windows and may help you find the differences.
>>
>> It was also failing on MacOS. And it failed a different way on another Windows version. That's why I removed the test for the deterministic shuffle.
>>
>>> I tend to agree with your `I think it's just a case where Windows' algorithm for std::mt19937 is subtly different than the one for Linux.`
>>
>> The only other option would be to add the `EXPECT_*` stuff on one platform (like Linux). I suppose that would be better than nothing.
>
> Here's what has me confused... You're using `std::mt19937` which is a very specific random number algorithm and you're giving it the same seed. I don't think we *should* be getting different behavior from the random number generator across platforms. The issue is the call to `std::shuffle` (see https://en.cppreference.com/w/cpp/algorithm/random_shuffle#Notes), so I think using `llvm::shuffle` will fix all the tests on all the platforms.

Okay. So I'll make this change and submit it during a time when there isn't a lot of activity so that I can revert it if it fails without annoying too many people.


Repository:
  rG LLVM Github Monorepo

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  https://reviews.llvm.org/D121556/new/

https://reviews.llvm.org/D121556