build: Use Link Time Optimization in Qt code for Darwin hosts #25744

pull hebasto wants to merge 1 commits into bitcoin:master from hebasto:220729-qt-darwin-lto changing 2 files +4 −0

hebasto commented at 9:46 PM on July 29, 2022: member
While building the qt package in depends succeeds, the following configure script fails with:
```
...
LLVM ERROR: Unexistent dir: '/tmp/cc-dea72a.o'
clang: error: linker command failed with exit code 1 (use -v to see invocation)
...
```
when checking for QMinimalIntegrationPlugin.
build: Use Link Time Optimization in Qt code for Darwin hosts e00910f41b
DrahtBot added the label Build system on Jul 29, 2022
fanquake commented at 8:23 AM on July 30, 2022: member

the following configure

what configure?
hebasto commented at 10:17 AM on July 30, 2022: member
the following configure

what configure?
```
./configure CONFIG_SITE=$PWD/depends/x86_64-apple-darwin/share/config.site
```
fanquake commented at 10:24 AM on July 30, 2022: member

I'm confused, because that works for master. I assume it's only started failing after you've introduced the additional changes in this PR?
hebasto commented at 10:45 AM on July 30, 2022: member
I'm confused

So do I :)

because that works for master.

LTO does not work in Qt code for Darwin hosts on the master branch:
```
$ make -C depends qt_configured HOST=x86_64-apple-darwin LTO=1
...
Build options:
...
  Using LTCG ............................. no
...
```
Just adding (package)_config_opts_darwin += -ltcg makes building of the qt package fail.

I assume it's only started failing after you've introduced the additional changes in this PR?

After current changes building of the qt package with LTO=1 succeeds.
fanquake commented at 10:52 AM on July 30, 2022: member

LTO does not work in Qt code for Darwin hosts on the master branch:

It does. It just doesn't use Qts special ltcg mode. That isn't actually required to build binaries with LTO.
in depends/patches/qt/mac-qmake.conf:21 in e00910f41b
```
  17 | @@ -18,5 +18,6 @@ QMAKE_MAC_SDK.macosx.PlatformPath = /phony
  18 |  !host_build: QMAKE_CXXFLAGS += -target $${MAC_TARGET}
  19 |  !host_build: QMAKE_LFLAGS += -target $${MAC_TARGET}
  20 |  QMAKE_AR = $${CROSS_COMPILE}ar cq
  21 | +QMAKE_AR_LTCG = llvm-ar cqs
```
fanquake commented at 10:56 AM on July 30, 2022:

Shouldn't this be an ar from our binutils? Otherwise isn't this requiring llvm to be installed?
fanquake commented at 2:53 PM on August 4, 2022:

Tested this branch, without llvm (which shouldn't become a dependency), this will fail with:

make[4]: llvm-ar: No such file or directory

Any reason we can't do?

QMAKE_AR_LTCG = $${CROSS_COMPILE}ar cqs
hebasto commented at 11:15 AM on August 6, 2022:

It does not work.
hebasto closed this on Aug 6, 2022
bitcoin locked this on Aug 6, 2023

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