[tree-ssa] Lazy updating of stmt operands

[Zdenek Dvorak]

Hello,

what is the purpose of having lists of stmt operands updated on demand?
I thought that it is for performance reasons, but this seems not to be
the case as all the statements are anyway scanned in the final dce pass,
so they end up in updated forms and we cannot gain anything elsewhere.

Why I am interested in this is that it prevents us from having also
def-use edges (immediate uses) provided explicitly, which would be
convenient in two cases I have encountered recently.

Zdenek