The patch you described would modify the altivec.md file in the rs6000 directory of the GCC 9.2.0 compiler's configuration. This configuration file defines the instruction patterns used by the compiler for AltiVec instructions on IBM RS/6000 and PowerPC processors.

The change you mentioned would add an extra condition to the TARGET_ALTIVEC macro that checks whether it is non-zero. Specifically, the new condition && 0 would always evaluate to false, effectively disabling the TARGET_ALTIVEC feature.

It's hard to say what the practical effect of this change would be without knowing more about the context, but it may be used to selectively disable AltiVec support for certain code paths or to work around a particular issue or bug.