Failure to optimize strcpy+strchr of 0 to stpcpy

[GabrielRavier]

Bugzilla Link	47144
Version	trunk
OS	Linux
CC	@davidbolvansky,@efriedma-quic

Extended Description

char *f(char *a, const char *b)
{
strcpy(a, b);
return strchr(a, '\0');
}

This can be optimized to return stpcpy(a, b);. This transformation is done by GCC, but not by LLVM.

[davidbolvansky]

Eli, where should we handle case like this (and many similar ones)?

In SLC/InstCombine we dont have MemoryDepAnalysis to know that strcpy(a, b) is last call which touches a.

[efriedma-quic]

I think doing this sort of thing well requires some sort of string equivalent to memcpyopt. I'm not sure it's really worth the effort, though.