This is a reduced testcase from a large codebase for 32-bit ARM microcontrollers.<\/p>
Yesterday I noticed that GCC 12 generates the exact same code in C++17 and C++20 mode.<\/p>
This morning, a GCC developer guessed the issue and pointed me at the fix that was merged two years ago.<\/p>
I can't update my toolchain right now, but knowing what triggers the bug made it easy to come up with a workaround for GCC 10.<\/p>
#programming<\/a> #cpp<\/a> #embedded<\/a> #gcc<\/a><\/p>","generator":{"id":"tag:bobinas.p4g.club,2026-05-08:notice-source:ActivityPub","objectType":"application","status_net":{"source_code":"ActivityPub"}},"id":"https:\/\/mstdn.io\/users\/codewiz\/statuses\/109814820347523235","object":{"id":"https:\/\/mstdn.io\/users\/codewiz\/statuses\/109814820347523235","objectType":"note","content":" This is a reduced testcase from a large codebase for 32-bit ARM microcontrollers.<\/p> Yesterday I noticed that GCC 12 generates the exact same code in C++17 and C++20 mode.<\/p> This morning, a GCC developer guessed the issue and pointed me at the fix that was merged two years ago.<\/p> I can't update my toolchain right now, but knowing what triggers the bug made it easy to come up with a workaround for GCC 10.<\/p> #programming<\/a> #cpp<\/a> #embedded<\/a> #gcc<\/a><\/p>","url":"https:\/\/mstdn.io\/@codewiz\/109814820347523235","status_net":{"notice_id":null},"inReplyTo":{"objectType":"note","id":"https:\/\/mstdn.io\/users\/codewiz\/statuses\/109814779164581115","url":"https:\/\/mstdn.io\/@codewiz\/109814779164581115"},"tags":[{"objectType":"http:\/\/activityschema.org\/object\/hashtag","displayName":"cpp"},{"objectType":"http:\/\/activityschema.org\/object\/hashtag","displayName":"embedded"},{"objectType":"http:\/\/activityschema.org\/object\/hashtag","displayName":"gcc"}]},"to":[{"objectType":"http:\/\/activitystrea.ms\/schema\/1.0\/collection","id":"http:\/\/activityschema.org\/collection\/public"}],"status_net":{"conversation":"tag:bobinas.p4g.club,2023-02-05:objectType=thread:nonce=4e2733d0cba236f3","notice_info":{"local_id":"1471149","source":"ActivityPub"}},"published":"2023-02-05T23:53:07+00:00","provider":{"objectType":"service","displayName":"Bobinas P4G","url":"https:\/\/bobinas.p4g.club\/"},"verb":"post","url":"https:\/\/mstdn.io\/@codewiz\/109814820347523235"},{"actor":{"id":"https:\/\/mstdn.io\/users\/codewiz","displayName":"Bernie","status_net":{"avatarLinks":[{"url":"https:\/\/bobinas.p4g.club\/avatar\/7840-96-20190817143304.png","rel":"avatar","type":"image\/png","width":96,"height":96},{"url":"https:\/\/bobinas.p4g.club\/avatar\/7840-48-20190817143304.png","rel":"avatar","type":"image\/png","width":48,"height":48},{"url":"https:\/\/bobinas.p4g.club\/avatar\/7840-24-20190817143329.png","rel":"avatar","type":"image\/png","width":24,"height":24}],"profile_info":{"local_id":"7840"}},"image":{"url":"https:\/\/bobinas.p4g.club\/avatar\/7840-96-20190817143304.png","rel":"avatar","type":"image\/png","width":96,"height":96},"objectType":"person","summary":"\ud83c\uddee\ud83c\uddf9 \u2192 \ud83c\uddfa\ud83c\uddf8 \u2192 \ud83c\uddef\ud83c\uddf5 \u2192 \ud83c\uddf9\ud83c\udded \u2192 \ud83d\ude80Nomadic Linux developer, currently in Los Angeles.#linux #rust #anime #spacex #cycling #travel #vegan #retrocomputing #amiga #fedi22\ud835\udc68\ud835\udc74\ud835\udc70\ud835\udc6e\ud835\udc68 :amiga:","url":"https:\/\/mstdn.io\/@codewiz","portablecontacts_net":{"preferredUsername":"codewiz","displayName":"Bernie","note":"\ud83c\uddee\ud83c\uddf9 \u2192 \ud83c\uddfa\ud83c\uddf8 \u2192 \ud83c\uddef\ud83c\uddf5 \u2192 \ud83c\uddf9\ud83c\udded \u2192 \ud83d\ude80Nomadic Linux developer, currently in Los Angeles.#linux #rust #anime #spacex #cycling #travel #vegan #retrocomputing #amiga #fedi22\ud835\udc68\ud835\udc74\ud835\udc70\ud835\udc6e\ud835\udc68 :amiga:"}},"content":" C++ compiler puzzle: can you guess why GCC 10.3 generates slightly worse code when switching from -std=c++17 to -std=c++20?<\/p> https:\/\/godbolt.org\/z\/99z7jxM1c<\/a> C++ compiler puzzle: can you guess why GCC 10.3 generates slightly worse code when switching from -std=c++17 to -std=c++20?<\/p> https:\/\/godbolt.org\/z\/99z7jxM1c<\/a>
#cpp<\/a> #programming<\/a> #cpp20<\/a> #assembly<\/a> #gcc<\/a> #compilers<\/a><\/p>","generator":{"id":"tag:bobinas.p4g.club,2026-05-08:notice-source:ActivityPub","objectType":"application","status_net":{"source_code":"ActivityPub"}},"id":"https:\/\/mstdn.io\/users\/codewiz\/statuses\/109814779164581115","object":{"id":"https:\/\/mstdn.io\/users\/codewiz\/statuses\/109814779164581115","objectType":"note","content":"
#cpp<\/a> #programming<\/a> #cpp20<\/a> #assembly<\/a> #gcc<\/a> #compilers<\/a><\/p>","url":"https:\/\/mstdn.io\/@codewiz\/109814779164581115","status_net":{"notice_id":null},"tags":[{"objectType":"http:\/\/activityschema.org\/object\/hashtag","displayName":"assembly"},{"objectType":"http:\/\/activityschema.org\/object\/hashtag","displayName":"compilers"},{"objectType":"http:\/\/activityschema.org\/object\/hashtag","displayName":"cpp"},{"objectType":"http:\/\/activityschema.org\/object\/hashtag","displayName":"cpp20"},{"objectType":"http:\/\/activityschema.org\/object\/hashtag","displayName":"gcc"},{"objectType":"http:\/\/activityschema.org\/object\/hashtag","displayName":"programming"}]},"to":[{"objectType":"http:\/\/activitystrea.ms\/schema\/1.0\/collection","id":"http:\/\/activityschema.org\/collection\/public"}],"status_net":{"conversation":"tag:bobinas.p4g.club,2023-02-05:objectType=thread:nonce=4e2733d0cba236f3","notice_info":{"local_id":"1471146","source":"ActivityPub"}},"published":"2023-02-05T23:42:40+00:00","provider":{"objectType":"service","displayName":"Bobinas P4G","url":"https:\/\/bobinas.p4g.club\/"},"verb":"post","url":"https:\/\/mstdn.io\/@codewiz\/109814779164581115"}],"links":[{"url":"https:\/\/bobinas.p4g.club\/conversation\/1011096","rel":"alternate","type":"text\/html"}]}