[cfe-dev] About option `-flax-vector-conversions`

[Zeson Wu via cfe-dev]

Hi, all.

I am considering that why the default value of -flax-vector-conversions is
open. I am supposed to turn off this option as default, which is forbidding
implicit vector conversions between different vector type. If you really
need conversion, use explicit conversion operator.

I think this option would cover potential bugs. I am developing in PPC
platform about altivec. With `-fno-lax-vector-conversions` option, I can
find some bugs in altivec.h easily in compile-time. There is also a related
bug report about this option.https://llvm.org/bugs/show_bug.cgi?id=17164

Anyway, it's better to forbid implicit vector conversions between different
vector type. Instead, use explicit conversion operation as needed. Now, the
altivec.h can not compiled successfully with
`-fno-lax-vector-conversions`since a lot of explicit conversion operators
are needed add.

-- 
Zeson
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