Add -memprofile option to l-tm

[pwaller]

For profiling memory allocations used for producing reproducible
instructions for analysing allocations.

Usage:

This command collects a profile:

l-tm -memprofile=mem.pprof <input llvm>

This one loads pprof in a mode showing all allocations that occurred by
count (rather than by size, which is alloc_space).

go tool pprof -sample_index=alloc_objects mem.pprof

Useful commands thereafter: top10 or web.

[pwaller]

For the record, here's what the output looks like at the moment on master:

~/.local/src/github.com/llir/testdata/sqlite/test$ l-tm -memprofile=shell.pprof shell.ll
=== [ shell.ll ] =======================

asm: parsing into AST took: 7.070239753s
asm: index AST top-level entities took: 470.742966ms
asm: type resolution took: 41.021963ms
asm: create IR top-level entities took: 364.503029ms
asm: translate AST to IR took: 29.626707477s
total time for file "shell.ll": 37.628816642s

~/.local/src/github.com/llir/testdata/sqlite/test$ go tool pprof -sample_index=alloc_objects shell.pprof

File: l-tm
Type: alloc_objects
Time: Dec 9, 2018 at 3:13pm (GMT)
Entering interactive mode (type "help" for commands, "o" for options)

(pprof) top10
Showing nodes accounting for 13835477, 85.07% of 16263763 total
Dropped 374 nodes (cum <= 81318)
Showing top 10 nodes out of 89
      flat  flat%   sum%        cum   cum%
   5987566 36.82% 36.82%    5987566 36.82%  github.com/llir/ll/ast.(*builder).addNode
   4045040 24.87% 61.69%    4045040 24.87%  github.com/llir/ll/ast.ToLlvmNode
   1211043  7.45% 69.13%    1211043  7.45%  github.com/llir/ll/ast.(*Node).Children
    682002  4.19% 73.33%     682002  4.19%  github.com/llir/ll/selector.OneOf
    443999  2.73% 76.06%     443999  2.73%  strconv.syntaxError (inline)
    404527  2.49% 78.54%     404527  2.49%  github.com/llir/llvm/asm.(*generator).astToIRIntType
    375321  2.31% 80.85%    1278388  7.86%  github.com/llir/llvm/asm.(*generator).astToIRPointerType
    231762  1.43% 82.28%     696437  4.28%  github.com/llir/llvm/asm.(*generator).irMetadataAttachment
    231762  1.43% 83.70%     928199  5.71%  github.com/llir/llvm/asm.(*generator).irMetadataAttachments
    222455  1.37% 85.07%     222455  1.37%  github.com/llir/llvm/asm.(*generator).createMetadataDefs

[pwaller]

BTW, my assertion (offline) that it was 50% of allocations was erroneous, it looks like it is only 24% of allocations above - I must have been considering the cumulative number rather than the "individual method" number.

I still believe the ~10% wallclock speedup number, though.

[coveralls]

Coverage remained the same at 62.884% when pulling 3022db4 on memprofile-l-tm into bc6a508 on master.

[mewmew]

LGTM.