Compiler allocations are sensitive to environment variables
It turns out that GHC's allocations are quite sensitive to environment variables:
$ HI="$(yes | head -n 10000)" ghc -Rghc-timing
ghc: no input files
Usage: For basic information, try the `--help' option.
<<ghc: 17523568 bytes, 17 GCs, 1243182/2375192 avg/max bytes residency (4 samples), 6M in use, 0.001 INIT (0.001 elapsed), 0.010 MUT (0.010 elapsed), 0.053 GC (0.054 elapsed) :ghc>>
$ HI="" ghc -Rghc-timing
ghc: no input files
Usage: For basic information, try the `--help' option.
<<ghc: 16368120 bytes, 16 GCs, 908760/1347632 avg/max bytes residency (3 samples), 5M in use, 0.001 INIT (0.000 elapsed), 0.009 MUT (0.009 elapsed), 0.036 GC (0.037 elapsed) :ghc>>I suspect that the reason is the use of System.Environment.getEnvironment (which decodes all environment variables into Haskell Strings) in GHC.HandleEncoding.configureHandleEncoding. This could easily be changed to rather use getEnv, which is far more surgical.