[llvm-bugs] [Bug 50043] New: [ObjC ARC][Objc block][noescape][rvalue] Objects captured by objc blocks get destructed before the block invocation

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=50043

            Bug ID: 50043
           Summary: [ObjC ARC][Objc block][noescape][rvalue] Objects
                    captured by objc blocks get destructed before the
                    block invocation
           Product: clang
           Version: trunk
          Hardware: Macintosh
                OS: MacOS X
            Status: NEW
          Severity: release blocker
          Priority: P
         Component: C++
          Assignee: unassignedclangbugs at nondot.org
          Reporter: xiaoranxu.nju at gmail.com
                CC: blitzrakete at gmail.com, dgregor at apple.com,
                    erik.pilkington at gmail.com, llvm-bugs at lists.llvm.org,
                    richard-llvm at metafoo.co.uk

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: https://reviews.llvm.org/D81624

-- 
You are receiving this mail because:
You are on the CC list for the bug.
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.llvm.org/pipermail/llvm-bugs/attachments/20210420/e12b09a3/attachment.html>