[Bug 1279128] [NEW] change dpkg-buildflags to default to -O3, not -O2, on ppc64el

[Steve Langasek]

Public bug reported:

Per Debian policy, dpkg currently defaults to -O2 for optimization flags
on all architectures.  According to people more familiar with the
architecture than I, -O3 is a better default for ppc64el; because while
-O2 includes only those optimizations that *always* improve performance,
whereas -O3 includes optimizations that will sometimes *decrease*
performance, the architecture-specific trade-offs on POWER mean that -O3
is better for the vast majority of real software, and far outweighs any
downsides.

So for ppc64/ppc64el, dpkg should default to -O3 in dpkg-buildflags, not
-O2.

It may be the case that we should make this same change for other
architectures as well, but not before proving that there's a benefit.
The change should also be forwarded to Debian, but that will mean
discussing first whether and with what evidence to change Debian policy.

** Affects: dpkg (Ubuntu)
     Importance: Undecided
     Assignee: Matthias Klose (doko)
         Status: New

** Changed in: dpkg (Ubuntu)
     Assignee: (unassigned) => Matthias Klose (doko)

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https://bugs.launchpad.net/bugs/1279128

Title:
  change dpkg-buildflags to default to -O3, not -O2, on ppc64el

Status in “dpkg” package in Ubuntu:
  New

Bug description:
  Per Debian policy, dpkg currently defaults to -O2 for optimization
  flags on all architectures.  According to people more familiar with
  the architecture than I, -O3 is a better default for ppc64el; because
  while -O2 includes only those optimizations that *always* improve
  performance, whereas -O3 includes optimizations that will sometimes
  *decrease* performance, the architecture-specific trade-offs on POWER
  mean that -O3 is better for the vast majority of real software, and
  far outweighs any downsides.

  So for ppc64/ppc64el, dpkg should default to -O3 in dpkg-buildflags,
  not -O2.

  It may be the case that we should make this same change for other
  architectures as well, but not before proving that there's a benefit.
  The change should also be forwarded to Debian, but that will mean
  discussing first whether and with what evidence to change Debian
  policy.

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