Extremely slow macro expansion

[mikebenfield]

See this gist.

Here is a chart giving real time output from time rustc main.rs -o out with n of the lines of the form [0xDD, 0xCB, d, 0x00 ] uncommented.

n	sec
100	0.561
200	1.457
300	3.042
400	5.474
500	8.061
600	12.364
700	17.520
800	25.105
900	37.410
1000	48.006
1100	72.33

With this gist I've tried to create a fairly minimal example. It's not as minimal as maybe it could be because it's a little tricky to figure out what's causing the slow compiles and I've spent as much time as I can on this right now. It's very sensitive to seemingly irrelevant changes in the code. If I remove the unused count variable, compile times dramatically improve. If I remove the empty for loop, compile times dramatically improve.

On my actual project, I am getting compile times in excess of 20 minutes. To compile a few thousand lines of code.

[arielb1]

cc @jseyfried

[arielb1]

Umm this is not an expansion problem but rather a borrowck problem - dataflow somehow takes O(n) iterations to converge.