reduce 1.5x memory usage on large repos on repeated runs

[jirfag]

Get rid of AST cache: load AST when needed. Optimize memory allocations
for go/analysis actions.

Relates: #337

[ernado]

LGTM.

BTW still getting OOM'ed on kubernetes codebase :(

Showing nodes accounting for 4195.99MB, 72.50% of 5787.34MB total
Dropped 328 nodes (cum <= 28.94MB)
Showing top 10 nodes out of 150
      flat  flat%   sum%        cum   cum%
 2838.82MB 49.05% 49.05%  2911.32MB 50.31%  honnef.co/go/tools/ssa.memberFromObject
  260.05MB  4.49% 53.55%   958.12MB 16.56%  honnef.co/go/tools/ssa.makeWrapper
  254.66MB  4.40% 57.95%   275.16MB  4.75%  go/types.methodSet.add
  156.67MB  2.71% 60.65%   485.84MB  8.39%  go/types.NewMethodSet
  134.01MB  2.32% 62.97%   134.01MB  2.32%  go/types.(*Selection).Type
  119.79MB  2.07% 65.04%   119.79MB  2.07%  golang.org/x/tools/go/types/typeutil.Hasher.Hash
  118.60MB  2.05% 67.09%   118.60MB  2.05%  go/types.(*Checker).recordTypeAndValue
  109.15MB  1.89% 68.97%  1071.27MB 18.51%  honnef.co/go/tools/ssa.(*Program).addMethod
  105.71MB  1.83% 70.80%   105.71MB  1.83%  bytes.makeSlice
   98.52MB  1.70% 72.50%    98.52MB  1.70%  honnef.co/go/tools/ssa.(*Function).newBasicBlock

inuse:

 1582.61MB 51.06% 51.06%  1634.11MB 52.72%  honnef.co/go/tools/ssa.memberFromObject
  199.08MB  6.42% 57.48%   199.08MB  6.42%  bytes.makeSlice
   87.07MB  2.81% 60.29%    87.07MB  2.81%  go/types.(*Checker).recordTypeAndValue
   80.52MB  2.60% 62.89%   306.54MB  9.89%  honnef.co/go/tools/ssa.makeWrapper
   63.03MB  2.03% 64.92%    69.03MB  2.23%  go/types.methodSet.add
   53.50MB  1.73% 66.65%    53.50MB  1.73%  honnef.co/go/tools/ssa.NewConst
   49.60MB  1.60% 68.25%    49.60MB  1.60%  golang.org/x/tools/go/types/typeutil.Hasher.Hash
   44.50MB  1.44% 69.68%    44.50MB  1.44%  go/types.NewParam
   42.72MB  1.38% 71.06%    42.72MB  1.38%  go/scanner.(*Scanner).scanString
   40.03MB  1.29% 72.35%   122.06MB  3.94%  go/types.NewMethodSet

pprof.golangci-lint.alloc_objects.alloc_space.inuse_objects.inuse_space.004.pb.gz

[jirfag]

@ernado did you try disabling unused?

[ernado]

@jirfag I've tried right now, and it is much better:

172.86user 3.05system 0:28.17elapsed 624%CPU (0avgtext+0avgdata 1581020maxresident)k
226720inputs+42408outputs (5major+594733minor)pagefaults 0swaps

So just 1.5Gb RSS, very cool.

[jirfag]

It's good. We need to add information about unused and GOMAXPROCS into README into the memory section. I will look at it at the weekend