This is not what "C users" want. It's what stubborn old timers unwilling to fix/replace their buggy code want. https://twitter.com/hashbreaker/status/668711545157853184 …
@CopperheadSec @dotstdy Inconsistent value quickly turns in to runaway UB. Almost impossible to stop that.
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@RichFelker@dotstdy True, it's not really what people want... but it can be useful to have those more permissive semantics. -
@RichFelker@dotstdy Could have a way to force a consistent but unspecified value from undefined reads but it could hurt performance a lot. -
@CopperheadSec@dotstdy Yes, any potentially UB read would have to be performed as if it were volatile. -
@RichFelker@dotstdy Well, it would need to reserve registers for uninitialized data and actually spill/restore them. -
@RichFelker@dotstdy So the main cost would probably be increased register pressure. It could get quite bad in some cases. -
@RichFelker@dotstdy http://llvm.org/docs/LangRef.html#undefined-values … and http://llvm.org/docs/LangRef.html#poison-values … are essentially what compilers actually want (basically lazy UB). -
@RichFelker@dotstdy Those aren't much more useful than outright UB, but it's at least a bit friendlier with no performance cost. -
@RichFelker@dotstdy Compilers don't actually like strict UB semantics because it means signed addition, etc. can have a side effect. - 3 more replies
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