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build: add lto configure option #10800

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@theuni @jonasschnelli @fanquake
@theuni
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theuni commented Jul 12, 2017

Addresses #10616. Please see the commit messages and note that AR/RANLIB may need to be set manually!

This is testing the waters for LTO. There are a few unknowns:

  • A boost LTO issue was addressed here, but others may remain for different libs/versions
  • ar/ranlib detection will likely turn out to be annoying
  • Not yet tested with Gitian

I propose adding this as-is (maybe after Gitian testing), and seeking feedback. I suspect that there will be quite a few platforms/toolchains where it's broken, but there's only so much we can do about it.

theuni added some commits Jul 11, 2017

@theuni theuni lto: workaround for boost issue 
I'm not sure what the root cause of the issue is yet, but defining a
boost::filesystem::path at global scope breaks linking with lto. The issue is
either:
- Some non-obvious ODR violation
- A bug or UB in gcc's handling of where to put the symbol for the inlined dtor
- Same as above, but for ld at link time

Presumably this is caused by the fact that boost::filesystem::path contains a
few methods which use static instances of a path object,

The work-around is to use a static string instead.
 1827368
@theuni theuni lto: add --enable-lto option 
Note that for gcc, AR and RANLIB may need to be manually set to gcc-ar and
gcc-ranlib respectively.

Depending on how much trouble this causes, we may need to attempt to set these.
e05d1c2

fanquake added the Build system label Jul 12, 2017

@jonasschnelli
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jonasschnelli commented Jul 12, 2017

Built successfully on my gitian machine (haven't tested the build yes though): https://bitcoin.jonasschnelli.ch/build/213
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