About option `-flax-vector-conversions`

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-conversionssince a lot of explicit conversion operators are needed add.