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[209.85.218.42]) by smtp.gmail.com with ESMTPSA id a640c23a62f3a-ab384f87cedsm397706166b.141.2025.01.18.13.28.04 for (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Sat, 18 Jan 2025 13:28:04 -0800 (PST) Received: by mail-ej1-f42.google.com with SMTP id a640c23a62f3a-aaec61d0f65so699954666b.1 for ; Sat, 18 Jan 2025 13:28:04 -0800 (PST) X-Forwarded-Encrypted: i=1; AJvYcCVeB/9ro434ogNFpWAmKR93yz3+JIOJ/o1mLfWFgHMJnGKxKHfV8jfr+2WIMmJKtVNO39F44sUUuw==@kvack.org X-Received: by 2002:a17:907:7e93:b0:aa6:6ea7:e5a7 with SMTP id a640c23a62f3a-ab38b190f6dmr725958666b.28.1737235315191; Sat, 18 Jan 2025 13:21:55 -0800 (PST) MIME-Version: 1.0 References: <34d53778977747f19cce2abb287bb3e6@AcuMS.aculab.com> <20250118170959.3aa56f4d@pumpkin> <29ef57a1-e4dd-4d5d-8726-f1f79c698b66@roeck-us.net> In-Reply-To: <29ef57a1-e4dd-4d5d-8726-f1f79c698b66@roeck-us.net> From: Linus Torvalds Date: Sat, 18 Jan 2025 13:21:39 -0800 X-Gmail-Original-Message-ID: X-Gm-Features: AbW1kvYv-hMWPkhbpIj1M-_2IHkjo_-SJWP7s5FFXlSWPKQ3TuGFR5sriOZzFKI Message-ID: Subject: Re: Buiild error in i915/xe (was: [PATCH next 4/7] minmax.h: Use BUILD_BUG_ON_MSG() for the lo < hi test in clamp()) To: Guenter Roeck Cc: David Laight , David Laight , Arnd Bergmann , "linux-kernel@vger.kernel.org" , Jens Axboe , Matthew Wilcox , Christoph Hellwig , Andrew Morton , Andy Shevchenko , Dan Carpenter , "Jason A . Donenfeld" , "pedro.falcato@gmail.com" , Mateusz Guzik , "linux-mm@kvack.org" , Lorenzo Stoakes , intel-xe@lists.freedesktop.org, intel-gfx@lists.freedesktop.org, David Airlie , Simona Vetter , Jani Nikula , Rodrigo Vivi Content-Type: text/plain; charset="UTF-8" X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: 6129A40006 X-Stat-Signature: kb6hdku3z3de4qngzqyswtgeejt55ick X-Rspam-User: X-HE-Tag: 1737235691-15004 X-HE-Meta: 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 csyqu1L3 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.006498, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Sat, 18 Jan 2025 at 09:49, Guenter Roeck wrote: > > No idea why the compiler would know that the values are invalid. It's not that the compiler knows tat they are invalid, but I bet what happens is in scale() (and possibly other places that do similar checks), which does this: WARN_ON(source_min > source_max); ... source_val = clamp(source_val, source_min, source_max); and the compiler notices that the ordering comparison in the first WARN_ON() is the same as the one in clamp(), so it basically converts the logic to if (source_min > source_max) { WARN(..); /* Do the clamp() knowing that source_min > source_max */ source_val = clamp(source_val, source_min, source_max); } else { /* Do the clamp knowing that source_min <= source_max */ source_val = clamp(source_val, source_min, source_max); } (obviously I dropped the other WARN_ON in the conversion, it wasn't relevant for this case). And now that first clamp() case is done with source_min > source_max, and it triggers that build error because that's invalid. So the condition is not statically true in the *source* code, but in the "I have moved code around to combine tests" case it now *is* statically true as far as the compiler is concerned. Linus