[llvm-bugs] [Bug 47411] New: False negative of -Winteger-overflow

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=47411

            Bug ID: 47411
           Summary: False negative of -Winteger-overflow
           Product: clang
           Version: trunk
          Hardware: PC
                OS: All
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: Frontend
          Assignee: unassignedclangbugs at nondot.org
          Reporter: mattdr at google.com
                CC: llvm-bugs at lists.llvm.org, neeilans at live.com,
                    richard-llvm at metafoo.co.uk

Repro at https://godbolt.org/z/1rorM4, code also copied below. See the
assignment of `does_not_warn`.

Compiled with default options using clang version 12.0.0
(https://github.com/llvm/llvm-project.git
96ef6998dfcc4d7f2c7fcb87eb9369e94a40e127)

===

#include <cstdint>
#include <iostream>
#include <utility>

struct HasAnInt64 {
    int64_t v;
};

int64_t g(HasAnInt64 s) { return 0; }

template<typename T>
int64_t g2(T s) { return 0; }

int main() {
    // Each of these raises a `-Winteger-overflow` diagnostic...
    int64_t warns1 = 512 * 1024 * 1024 * 1024;
    HasAnInt64 warns2{512 * 1024 * 1024 * 1024};
    int64_t warns3 = g({512 * 1024 * 1024 * 1024});
    int64_t warns4 = g2<HasAnInt64>({512 * 1024 * 1024 * 1024});

    // ... but not this one.
    auto does_not_warn = std::make_pair<int, HasAnInt64>(0, {512 * 1024 * 1024
* 1024});

    // Overflow occurs. This prints `0`.
    std::cout << does_not_warn.second.v << std::endl;

    return 0;
}

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