[InstCombine] Improve `foldDeadPhiWeb` compile time (#158057)

The foldDeadPhiWeb function identifies and removes small dead PHI webs,
it bails out if the web size exceeds threshold (16).

In the current implementation, when there is a phi node has large number
of users that most of them are phi nodes, we still push them on the
`Stack` even if the number of phi nodes user exceeds the threshold.

This patch checks the early stop condition when we push an unvisited phi
node on the `Stack`.
With this change, the wall duration of total instcombine pass decreased
from 523,649.276 ms to 208,687.042 ms in an our internal case.

0 files changed, 0 insertions, 0 deletions