[LLVMdev] C as used/implemented in practice: analysis of responses (original) (raw)
Joerg Sonnenberger joerg at britannica.bec.de
Thu Jul 2 09:07:32 PDT 2015
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On Wed, Jul 01, 2015 at 04:06:45PM +0100, Peter Sewell wrote:
- for some, OS developers are already routinely turning off optimisations for the sake of more predictable semantics, e.g. with fno-strict-aliasing.
This one is interesting, because the biggest problem with strict aliasing is that there is no standard compliant way to override it. The most basic issue is how the allocator is supposed to work internally. If you can fully inline malloc/free pairs, it is practically impossible to avoid aliasing conflicts.
Other important use cases are things like vectorizing access, which often means checking for the alignment of the data and casting to a more appropiate type. Not everyone wants to implement strlen in assembler, but writing a standard compliant and still fast implementation in C seems impossible.
Joerg
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