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startup time is quadratic in argc

From: Ambrose Feinstein
Subject: startup time is quadratic in argc
Date: Sat, 3 Feb 2018 17:47:45 -0800

I was surprised to discover this:

$ time ./bash -c : $(seq 1000)
0.01s wall 0.00s user 0.00s system
$ time ./bash -c : $(seq 10000)
0.40s wall 0.39s user 0.00s system
$ time ./bash -c : $(seq 20000)
1.32s wall 1.31s user 0.01s system
$ time ./bash -c : $(seq 40000)
4.57s wall 4.54s user 0.02s system

That's a fresh build of bash 4.4.18.  None of the other shells I have
handy exhibit this (zsh, ksh, dash).

The trouble seems to be that bind_args() reverses argv, which means
that push_args() has to insert each element from the left.

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