[PATCH] D86844: [LoopDeletion] Allows deletion of possibly infinite side-effect free loops

[Atmn Patel via Phabricator via llvm-commits]

atmnpatel added a comment.

In D86844#2484568 <https://reviews.llvm.org/D86844#2484568>, @fhahn wrote:

> In D86844#2481922 <https://reviews.llvm.org/D86844#2481922>, @xbolva00 wrote:
>
>>   int a, b;
>>   
>>   int f(void) {
>>       while (1) {
>>           if (a != b) return 1;
>>       }
>>       return 0;
>>   }
>>   
>>   int g(int a, int b) {
>>       while (1) {
>>           if (a != b) return 1;
>>       }
>>       return 0;
>>   }
>>
>> LLVM does not catch these cases; gcc does.
>>
>> https://godbolt.org/z/jW7son
>
> Looks like `must progress` does not get added? If it gets added to the IR the loops get removed: https://godbolt.org/z/77v17P

I might be misunderstanding the standard here but since 1 is a non-zero constant expression, it can't be assumed to terminate by the implementation right? The relevant section from C11 at least is "An iteration statement whose controlling expression is not a constant expression that performs [explanation of what it deems as progress] may be assumed by the implementation to terminate" (C11 6.8.5 p6).


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