Am Freitag, dem 28.02.2025 um 21:39 +0300 schrieb Alexander Monakov: > On Fri, 28 Feb 2025, Martin Uecker via Gcc wrote: > > > > > I have one follow-up question: What is the reason > > that we have stronger semantics for stores by default (i.e. > > when not using -fallow-store-data-races) than for reads > > given that the standard would allow more freedom. > > Why would it? On the contrary, it makes an explicit note that > introducing new writes that could create a racing store is > not allowed, see note 13 in C11 5.1.2.4.
My original question was about inventing stores that currently seem to be allowed. Turning if (x != 1) x = 1; into x = 1; should be ok even though it invents a store for x == 1. While this technically introduces a race with another reader, it does so only in a seeminglessly harmless way when overwriting 1 with 1. Are you saying -fallow-store-data-races also introduces other kinds of races not allowed by C11? Martin > > > Only that for reads this is more difficult to have? > > Or other specific reasons why data races for stores > > are problematic? > > Introducing racing loads is generally not harmful, see note 14.
