On 30/12/2021 21:07, Jonas Maebe via fpc-devel wrote:
On 30/12/2021 21:03, Florian Klämpfl via fpc-devel wrote:
Yes, but the question is: if we load a shortint into a register, do we
need to sign extend it to 32/64 bit or not? I tend more and more to
say that we shouldn’t require this.
Neither clang nor gcc seem to expect this for arguments/return values:
https://godbolt.org/z/sv5fPP6GM
This is not related to arguments/return values. We do the same on on
PPC, and afaik on all architectures that don't have 8/16 bit
subregisters. I initially did it on PPC because it simplified code
generation a lot and solved all kinds of small issues I got otherwise
because non-cleared higher parts of registers were used. Maybe with our
current code generators it would work better.
Actually, the main reason may have been register variables: in the code
generator you don't know whether a register is a register variable or
not. So if you don't sign/zero extend values on initialising a register,
then you have to zero/sign extend them every time you read them. And
reading generally happens a lot more often than writing.
Jonas
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