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A comment on On C-optimizing compilers removing code that has undefined behavior. Parent comment

Re:On C-optimizing compilers removing code that has undefine... by GedByrne on Saturday June 17, 2017 @05:49AM (#14575076)
Then why isn't the code being disallowed? Why is it being silently removed in the middle of the night through an optimization back door?
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Re:On C-optimizing compilers removing code that has undefine... by pornel on Saturday June 17, 2017 @07:04AM (#14575305)
It is disallowed by the standard.

It's not disallowed by compilers, because they're deficient. In this case I'd guess compiler front-end doesn't track which values in an array are initialized, and when optimizing back-end sees UB it's too late to emit an error.

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