Why qmake passes -Wl,O1 to gcc when linking and will it harm LTO?
I noticed that in the default release configuration, qmake (qmake 3.1, qt 5.9.5 - whatever is installed on my Ubuntu build box) passes -Wl,O1 to g++ when linking. So the linking command line looks like
g++ -Wl,-O1 -flto -O2 -o program program.o lib1.a lib2.a ...
where -flto -O2 are the options that I'm passing via QMAKE_LFLAGS_RELEASE to enable LTO.
Now the question: why qmake has this -Wl,-O1 option and is it going to interfere with LTO?
gcc qmake
asked Nov 20 '18 at 1:30
Alexey B.Alexey B.
663314
add a comment |
I noticed that in the default release configuration, qmake (qmake 3.1, qt 5.9.5 - whatever is installed on my Ubuntu build box) passes -Wl,O1 to g++ when linking. So the linking command line looks like
g++ -Wl,-O1 -flto -O2 -o program program.o lib1.a lib2.a ...
where -flto -O2 are the options that I'm passing via QMAKE_LFLAGS_RELEASE to enable LTO.
Now the question: why qmake has this -Wl,-O1 option and is it going to interfere with LTO?
gcc qmake
asked Nov 20 '18 at 1:30
Alexey B.Alexey B.
663314
add a comment |
I noticed that in the default release configuration, qmake (qmake 3.1, qt 5.9.5 - whatever is installed on my Ubuntu build box) passes -Wl,O1 to g++ when linking. So the linking command line looks like
g++ -Wl,-O1 -flto -O2 -o program program.o lib1.a lib2.a ...
where -flto -O2 are the options that I'm passing via QMAKE_LFLAGS_RELEASE to enable LTO.
Now the question: why qmake has this -Wl,-O1 option and is it going to interfere with LTO?
gcc qmake
asked Nov 20 '18 at 1:30
Alexey B.Alexey B.
663314
I noticed that in the default release configuration, qmake (qmake 3.1, qt 5.9.5 - whatever is installed on my Ubuntu build box) passes -Wl,O1 to g++ when linking. So the linking command line looks like
g++ -Wl,-O1 -flto -O2 -o program program.o lib1.a lib2.a ...
where -flto -O2 are the options that I'm passing via QMAKE_LFLAGS_RELEASE to enable LTO.
Now the question: why qmake has this -Wl,-O1 option and is it going to interfere with LTO?
gcc qmake
gcc qmake
asked Nov 20 '18 at 1:30
Alexey B.Alexey B.
663314
asked Nov 20 '18 at 1:30
Alexey B.Alexey B.
663314
asked Nov 20 '18 at 1:30
Alexey B.Alexey B.
663314
asked Nov 20 '18 at 1:30
Alexey B.Alexey B.
663314
asked Nov 20 '18 at 1:30
Alexey B.Alexey B.
663314
663314
add a comment |
add a comment |
1 Answer
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QMake passes -Wl,O1, because it is meant to be a good default.
It will not harm LTO, because your -O2 option comes later and overrides the -Wl,O1.
From g++'s man page:
If you use multiple -O options, with or without level numbers, the
last such option is the one that is effective.
You can remove the -Wl,-O1 from your Makefile by specifying
QMAKE_LFLAGS_RELEASE -= -Wl,-O1
answered Nov 29 '18 at 8:49
hole-otter-rosyhole-otter-rosy
914
add a comment |
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1 Answer
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1 Answer
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active
oldest
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active
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votes
QMake passes -Wl,O1, because it is meant to be a good default.
It will not harm LTO, because your -O2 option comes later and overrides the -Wl,O1.
From g++'s man page:
If you use multiple -O options, with or without level numbers, the
last such option is the one that is effective.
You can remove the -Wl,-O1 from your Makefile by specifying
QMAKE_LFLAGS_RELEASE -= -Wl,-O1
answered Nov 29 '18 at 8:49
hole-otter-rosyhole-otter-rosy
914
add a comment |
QMake passes -Wl,O1, because it is meant to be a good default.
It will not harm LTO, because your -O2 option comes later and overrides the -Wl,O1.
From g++'s man page:
If you use multiple -O options, with or without level numbers, the
last such option is the one that is effective.
You can remove the -Wl,-O1 from your Makefile by specifying
QMAKE_LFLAGS_RELEASE -= -Wl,-O1
answered Nov 29 '18 at 8:49
hole-otter-rosyhole-otter-rosy
914
add a comment |
QMake passes -Wl,O1, because it is meant to be a good default.
It will not harm LTO, because your -O2 option comes later and overrides the -Wl,O1.
From g++'s man page:
If you use multiple -O options, with or without level numbers, the
last such option is the one that is effective.
You can remove the -Wl,-O1 from your Makefile by specifying
QMAKE_LFLAGS_RELEASE -= -Wl,-O1
answered Nov 29 '18 at 8:49
hole-otter-rosyhole-otter-rosy
914
QMake passes -Wl,O1, because it is meant to be a good default.
It will not harm LTO, because your -O2 option comes later and overrides the -Wl,O1.
From g++'s man page:
If you use multiple -O options, with or without level numbers, the
last such option is the one that is effective.
You can remove the -Wl,-O1 from your Makefile by specifying
QMAKE_LFLAGS_RELEASE -= -Wl,-O1
answered Nov 29 '18 at 8:49
hole-otter-rosyhole-otter-rosy
914
answered Nov 29 '18 at 8:49
hole-otter-rosyhole-otter-rosy
914
answered Nov 29 '18 at 8:49
hole-otter-rosyhole-otter-rosy
914
answered Nov 29 '18 at 8:49
hole-otter-rosyhole-otter-rosy
914
914
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add a comment |
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