build: improve __builtin_clz* detection #19403
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The way we currently test with AC_CHECK_DECLS do not work with Clang:
```bash
configure:21492: clang++-10 -std=c++11 -c -g -O2 -DHAVE_BUILD_INFO -D__STDC_FORMAT_MACROS conftest.cpp >&5
conftest.cpp:100:10: error: builtin functions must be directly called
(void) __builtin_clz;
^
1 error generated.
```
This also removes the __builtin_clz() check, as we don't actually use
it anywhere, and it's trvial to re-add detection if we do start using
it at some point.
sipa
reviewed
Jun 29, 2020
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ACK 9952242 |
1 similar comment
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ACK 9952242 |
luke-jr
pushed a commit
to bitcoinknots/bitcoin
that referenced
this pull request
Aug 15, 2020
The way we currently test with AC_CHECK_DECLS do not work with Clang:
```bash
configure:21492: clang++-10 -std=c++11 -c -g -O2 -DHAVE_BUILD_INFO -D__STDC_FORMAT_MACROS conftest.cpp >&5
conftest.cpp:100:10: error: builtin functions must be directly called
(void) __builtin_clz;
^
1 error generated.
```
This also removes the __builtin_clz() check, as we don't actually use
it anywhere, and it's trvial to re-add detection if we do start using
it at some point.
Github-Pull: bitcoin#19403
Rebased-From: 9952242 (diff-minimised)
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Fixes #19402.
The way we currently test for
__builtin_clz*support withAC_CHECK_DECLSdoes not work with Clang:This also removes the
__builtin_clz()check, as we don't actually use it anywhere, and it's trvial to re-add detection if we do start using it at some point. If this is controversial then I'll add a test for it as well.