d2cca846

By: Tom Sydney Kerckhove <syd@cs-syd.eu>

Mutation: skip the GRE lookup in headNameMatches when no names configured

The ignore filter runs headNameMatches on every expression in every
instrumented module.  With a non-empty name list it peels the head and
looks the name up in the GlobalRdrEnv; with an empty list (the common
case — no `ignore` configured) that work is wasted, since the candidates
are matched against `[]`.  Short-circuit the empty-list case so the
default config pays nothing per expression.  Behaviour is unchanged
(`any (`elem` []) ...` was already False).

Timeline