[llvm-bugs] [Bug 39285] New: Structured binding confuses -Wfor-loop-analysis

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=39285

            Bug ID: 39285
           Summary: Structured binding confuses -Wfor-loop-analysis
           Product: new-bugs
           Version: 7.0
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: new bugs
          Assignee: unassignedbugs at nondot.org
          Reporter: namark at disroot.org
                CC: llvm-bugs at lists.llvm.org

This code

#include <cstdio>
#include <tuple>

int main() 
{
    const int n = 10;
    for
    (
        auto [i, j] = std::tuple(0, 1);
        i < n;
        ++i, ++j
    )
    {}
}

compiled with "-std=c++17 -Wfor-loop-analysis" options produces a warning:
<source>:9:13: warning: variable 'n' used in loop condition not modified in
loop body [-Wfor-loop-analysis]
        i < n; 
            ^

The problem seems to be caused by the use of structured binding in the for
loop.

I'm using clang version 7.0.0-svn341916-1~exp1~20180911120702.28
(branches/release_70), 
but it also reproduces with clang 5/6/7/trunk on godbolt.org.

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