[Bug c++/82557] New: Spurious -Wstrict-overflow warning with 32bit GCC

[vindrg at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=82557

            Bug ID: 82557
           Summary: Spurious -Wstrict-overflow warning with 32bit GCC
           Product: gcc
           Version: 6.3.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: vindrg at gmail dot com
  Target Milestone: ---

Created attachment 42370
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=42370&action=edit
Preprocessed settingsserializer.ii

Building qTox [qtox] on Debian 9 (stretch) i686 with GCC (Debian 6.3.0-18)
6.3.0 20170516 using -Wstrict-overflow produces a warning in the place where it
shouldn't.

It *does not* reproduce on amd64 system.

Here's output:

/somewhere/qTox.git/src/persistence/settingsserializer.cpp:267: error: assuming
signed overflow does not occur when simplifying conditional to constant
[-Werror=strict-overflow]
         if (g != -1) {
         ^~

Context [context]:

for (int g = -1; g < groups.size(); ++g) {
    // Save the group name, if any
    if (g != -1) {
         writeStream(stream, RecordTag::GroupStart);
         writeStream(stream, groups[g].toUtf8());
    }

    // ...
}


I could workaround it with:

if (static_cast<volatile int &>(g) != -1) {

Although maybe there is different solution?


[qtox] https://github.com/qTox/qTox
[context]
https://github.com/qTox/qTox/blob/084f3b06262b2ca8272238b2ec450d11840d7551/src/persistence/settingsserializer.cpp#L267