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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - [ObjC ARC][Objc block][noescape][rvalue] Objects captured by objc blocks get destructed before the block invocation"
href="https://bugs.llvm.org/show_bug.cgi?id=50043">50043</a>
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<th>Summary</th>
<td>[ObjC ARC][Objc block][noescape][rvalue] Objects captured by objc blocks get destructed before the block invocation
</td>
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<th>Product</th>
<td>clang
</td>
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<th>Version</th>
<td>trunk
</td>
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<th>Hardware</th>
<td>Macintosh
</td>
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<th>OS</th>
<td>MacOS X
</td>
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<th>Status</th>
<td>NEW
</td>
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<th>Severity</th>
<td>release blocker
</td>
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<th>Priority</th>
<td>P
</td>
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<th>Component</th>
<td>C++
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<th>Assignee</th>
<td>unassignedclangbugs@nondot.org
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<th>Reporter</th>
<td>xiaoranxu.nju@gmail.com
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<th>CC</th>
<td>blitzrakete@gmail.com, dgregor@apple.com, erik.pilkington@gmail.com, llvm-bugs@lists.llvm.org, richard-llvm@metafoo.co.uk
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<pre>When -fobjc-arc is enabled, if a block is passed as an argument to a function
whose corresponding parameter type is && rvalue and attributed as noescape, the
object captured by the block can get destructed before the block invocation.
The following code example demonstrates the issue.
#import <Foundation/Foundation.h>
template<typename Func>
void callTemplateBlock(__attribute__((noescape)) Func &&func) {
func();
}
static void test(){
NSString* str = @"test";
NSLog(@"before the block: %d", (int)str.length);
return callTemplateBlock( ^void(){
NSLog(@"inside the block:%d", (int)str.length);
});
}
$ clang++ -isysroot path_to_SDK ./main.mm -fobjc-link-runtime -fobjc-arc
# ./a.out
before the block: 4
inside the block:0
It looks the codegen assumes the block doesn't capture any value in this
scenario (noescape + rvalue + ARC). Removing the noescape attribute, or
replacing the Func && type to the concrete block type, or removing -fobjc-arc,
doesn't repro the issue.
This change may be related: <a href="https://reviews.llvm.org/D81624">https://reviews.llvm.org/D81624</a></pre>
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