On 2017.08.26 at 01:39 -0700, Andrew Pinski wrote: > > First let me put into some perspective on -Os usage and some history: > 1) -Os is not useful for non-embedded users > 2) the embedded folks really need the smallest code possible and > usually will be willing to afford the performance hit > 3) -Os was a mistake for Apple to use in the first place; they used it > and then GCC got better for PowerPC to use the string instructions > which is why -Oz was added :) > 4) -Os is used heavily by the arm/thumb2 folks in bare metal applications. > > Comparing -O3 to -Os is not totally fair on x86 due to the many > different instructions and encodings. > Compare it on ARM/Thumb2 or MIPS/MIPS16 (or micromips) where size is a > big issue. > I soon have a need to keep overall (bare-metal) application size down > to just 256k. > Micro-controllers are places where -Os matters the most. > > This comment does not help my application usage. It rather hurts it > and goes against what -Os is really about. It is not about reducing > icache pressure but overall application code size. I really need the > code to fit into a specific size.
For many applications using -flto does reduce code size more than just going from -O2 to -Os. -- Markus
