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Thu, 18 Jun 2026 12:20:50 -0700 (PDT) Precedence: bulk X-Mailing-List: llvm@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset=UTF-8 Date: Thu, 18 Jun 2026 12:20:48 -0700 Message-Id: Cc: "Nathan Chancellor" , "Nick Desaulniers" , "Bill Wendling" , "Justin Stitt" , "open list" , "open list:CLANG/LLVM BUILD SUPPORT:Keyword:b(?i:clang|llvm)b" Subject: Re: [PATCH ath-next] ath9k: eeprom: alias vpdTableI onto vpdTableL to shrink stack frame From: "Rosen Penev" To: =?utf-8?q?Toke_H=C3=B8iland-J=C3=B8rgensen?= , "Rosen Penev" , X-Mailer: aerc 0.21.0-0-g5549850facc2 References: <20260617234105.284358-1-rosenp@gmail.com> <87pl1ofa6t.fsf@toke.dk> In-Reply-To: <87pl1ofa6t.fsf@toke.dk> On Thu Jun 18, 2026 at 2:51 AM PDT, Toke H=C3=B8iland-J=C3=B8rgensen wrote: > Rosen Penev writes: > >> vpdTableL, vpdTableR, and vpdTableI are never live simultaneously. >> vpdTableL and vpdTableR are consumed during the frequency-interpolation >> step that writes vpdTableI; after the if/else they are never read >> again. Reuse vpdTableL for the interpolated result (what was >> vpdTableI), reducing the stack frame by one 256-byte array. >> >> The read-via-write in the else branch is safe: ath9k_hw_interpolate() >> receives vpdTableL[i][j] by value as a function argument before the >> return value is written back to vpdTableL[i][j]. >> >> Stack frame size change (x86_64, clang): >> before: 0x440 (1088 B) >> after: 0x330 (816 B) > > Huh? These are static variables, how is this affecting stack usage? > I assume this is against your previous (broken) patch? It's only broken on ARM + GCC. GCC + anything else and Clang + anything else is fine. > > Anyway, adding this kind of aliasing to fix a problem that you > introduced by changing working code with no real benefit is not an > improvement. I'm OK with fixing actual bugs, but this is just mindless > churn... Fixing actual bugs is the goal yes. It makes sense to split up into multiple parts IMO. > > -Toke