[llvm-dev] Non-determinism in LLVM codegen

[Hans Wennborg via llvm-dev]

On Tue, Dec 13, 2016 at 6:39 PM, Hans Wennborg <hans at chromium.org> wrote:
> On Tue, Dec 13, 2016 at 4:57 PM, Grang, Mandeep Singh via llvm-dev
> <llvm-dev at lists.llvm.org> wrote:
>> Everyone,
>>
>> The following patch to reverse iterate SmallPtrSet's has now been merged:
>> https://reviews.llvm.org/D26718
>>
>> This is how LLVM behavior will change due to this patch:
>> - In LLVM builds with assertions enabled, SmallPtrSet's would always be
>> reverse iterated by default.
>>   This default behavior can be overridden via the flag "-mllvm
>> -reverse-iterate=<true/false>".
>>
>> - In LLVM builds with assertions disabled, SmallPtrSet's would continue to
>> be always forward iterated.
>>   This behavior cannot be overridden as the above flag is available only in
>> builds with assertions enabled.
>>
>> Currently, the following unit tests are failing in Release+Asserts mode due
>> to the difference in SmallPtrSet iteration order:
>>     Clang :: Analysis/keychainAPI.m
>>     Clang :: Analysis/malloc.c
>>     Clang :: Rewriter/objc-modern-metadata-visibility.mm
>>     Clang :: SemaCXX/warn-loop-analysis.cpp
>>     LLVM :: Transforms/SimplifyCFG/bug-25299.ll
>
> Wait, so you committed a patch that breaks these tests? Should you fix
> them first?
>
> IIUC, LLVM_ABI_BREAKING_CHECKS is WITH_ASSERTS by default, so your
> change, which is known to break things, is enabled for those of us
> enabling asserts?
>
> Or am I misunderstanding?

Looks like Mehdi reverted already.