Compilation time regression in 1.73 when building the fundsp crate

[irh]

1.73 introduced a regression in compilation time when building the fundsp crate.

Previously, I could expect a clean build of the crate to take ~22s. Now, compilation hangs for several minutes, I haven't left it running longer than that.

I bisected to #114611, and 8378487 appears to be the commit that introduces the slowdown. Reverting the commit on the latest master brings fundsp build times back to normal.

[saethlin]

I think this is the same root cause as #116624 and #116780.

[Noratrieb]

@nnethercote

[nnethercote]

I think this is the same root cause as #116624 and #116780.

It is the same as #116780. It is not the same as #116624, which is slow even in 1.72.

[nnethercote]

Good news: #116826 will fix the regression.

Even better news: on my machine this crate took 3m13s to compile. After removing the 3rd and 4th commits from #114611, it dropped to 22s. After reinstating the 4th commit (because the 3rd commit was the problem) it dropped to 9s :)