Edits a hard-coded string in an unrolled loop
I was told in the IRC channel that the non optimized LLVM code I was getting of
the attached C++ code was related to this issue.
It becomes optimized when the string 's' becomes small, like "this".

Bug 1309 is also related to this.

example with poor memcpy optimization
In the last line
return r + x.A;
the value of x.A is zero, but LLVM doesn't understand this.
Presumably this is because it thinks memcpy has modified x,
even though it copies from x and not to it.

Bug 1952 is one specific optimization that we can do, relating it.

This has gotten a lot better recently, with work Chris and I have done which is now in the MemCpyOpt pass. There's still a lot to do, though.

I'm closing this open-ended bug, as we'll never catch EVERY case. If you still have specific cases that you'd like to see addressed, please file individual PRs for them.