[GHC] #9315: Weird change in allocation numbers of T9203

[GHC]

#9315: Weird change in allocation numbers of T9203
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              Reporter:  nomeata     |             Owner:  simonmar
                  Type:  bug         |            Status:  new
              Priority:  normal      |         Milestone:
             Component:  Runtime     |           Version:  7.9
  System                             |          Keywords:
            Resolution:              |  Operating System:  Unknown/Multiple
Differential Revisions:              |   Type of failure:  None/Unknown
          Architecture:              |         Test Case:
  Unknown/Multiple                   |          Blocking:
            Difficulty:  Unknown     |
            Blocked By:              |
       Related Tickets:              |
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Comment (by nomeata):

 > I suspect that adding -O2 to libraries and compiler (we would have to do
 both) would make validate  lower, but I don't know how much; feel free to
 measure it. I do think validate is too slow already,  though, and we
 should be finding ways to speed it up.

 I changed the builder for ghcspeed to set `Validating=YES`, and the time
 to run `make` was reduced by ¼. I didn’t measure the time for a whole
 validate run, I guess I’ll do that separately.

 But setting that changes more than just `GhcLibHcOpts`, e.g. it disables
 split objects (increasing binary sizes by a factor of 3.5).

 Allocation of nofib benchmarks wobble a bit, but significat changes are
 only on the increasing side (fish, +5%), so for nofib, the release
 settings seem to be better than the validate setting. (good!)

 The allocation number of #4801’s test case actually decreases by 4.7%. In
 total, 7 test cases now get *better* allocation numbers, while only
 `haddock.base` degrades by more than 1%.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9315#comment:14>
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