compile-time performance regression compiling genprimcode

compiling utils/genprimopcode (where compiling the Alex-generated Lexer takes up the most amount of time) with GHC 7.8.4:

$ time /opt/ghc/7.8.4/bin/ghc  -Rghc-timing --make -O Main.hs 
[1 of 5] Compiling ParserM          ( ParserM.hs, ParserM.o )
[2 of 5] Compiling Lexer            ( Lexer.hs, Lexer.o )
[3 of 5] Compiling Syntax           ( Syntax.hs, Syntax.o )
[4 of 5] Compiling Parser           ( Parser.hs, Parser.o )
[5 of 5] Compiling Main             ( Main.hs, Main.o )
Linking Main ...
<<ghc: 20742311240 bytes, 2092 GCs, 60174814/140258264 avg/max bytes residency (33 samples), 332M in use, 0.00 INIT (0.00 elapsed), 7.84 MUT (8.35 elapsed), 6.93 GC (6.93 elapsed) :ghc>>

real	0m15.331s
user	0m15.173s
sys	0m0.172s

(btw, is it ok that GC takes up so much?)

the same with a GHC 7.10 snapshot takes *alot* longer:

$ time /opt/ghc/7.10.1/bin/ghc  -Rghc-timing --make -O Main.hs 
[1 of 5] Compiling ParserM          ( ParserM.hs, ParserM.o )
[2 of 5] Compiling Lexer            ( Lexer.hs, Lexer.o )
[3 of 5] Compiling Syntax           ( Syntax.hs, Syntax.o )
[4 of 5] Compiling Parser           ( Parser.hs, Parser.o )
[5 of 5] Compiling Main             ( Main.hs, Main.o )
Linking Main ...
<<ghc: 147681534568 bytes, 37824 GCs, 203338614/375314176 avg/max bytes residency (538 samples), 876M in use, 0.001 INIT (0.001 elapsed), 81.374 MUT (81.888 elapsed), 235.240 GC (235.136 elapsed) :ghc>>

real	5m17.061s
user	5m16.702s
sys	0m0.499s

1. ..and here the GC/MUT ratio is even more off.