http://llvm.org/bugs/show_bug.cgi?id=13474
Bug #: 13474
Summary: Feature request: warning for unnecessary __block
keywords
Product: clang
Version: 3.1
Platform: Macintosh
OS/Version: MacOS X
Status: NEW
Severity: enhancement
Priority: P
Component: -New Bugs
AssignedTo: [email protected]
ReportedBy: [email protected]
CC: [email protected]
Classification: Unclassified
Since clang can detect variables that need to be annotated with the __block
keyword but are not, I was hoping the converse might be possible.
Specifically, consider:
#include <stdio.h>
int main(int argc, char **argv) {
__block int i;
for (i = 0; i < argc; i++) {
printf("argv[%d] is %s\n", i, argv[i]);
}
return 0;
}
Clang will happily compile this with -Wall -Wextra without a peep and will
generate code that allows 'i' to be used from a block (set-up extra state on
the stack and call Block_object_dispose()). Since there is a performance cost
in the emitted code, it would be nice if the compile could detect when __block
variables are not referenced from within a block and warn about it. Or,
alternatively, just optimize away the code for handling the block-ness.
I am using:
Apple clang version 3.1 (tags/Apple/clang-318.0.61) (based on LLVM 3.1svn)
Target: x86_64-apple-darwin11.4.0
Thread model: posix
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