On 5/17/2021 1:44 AM, Jonathan Wakely via Gcc-help wrote:
On Mon, 17 May 2021, 08:31 Ezhil P via Gcc-help, <gcc-help@xxxxxxxxxxx>
wrote:
Hi,
can you kindly clarify the unique feature of -Og flag?. It is described as
"optimize the debugging experience". How does it do?
It performs some simple optimizations that improve performance similarly to
-O1. But it avoids transformations that make debugging harder, such as
drastically rearranging the code, or GDB telling you a variable had been
"optimized out".
It's not magic, it's just a selection of optimizations that don't hurt the
debugging experience. The usual -O1, -O2, -O3 options aim for better
performance, not debugging experience, and -Os aims for smaller code size,
not debugging experience. So it's just a different set of trade offs.
-Og is also a good option in circumstances where you're compiling
insanely large code on a resource constrained system. The case we ran
into was auto-generated code that had tons of obvious redundancies. -Og
cleaned things up enough that we didn't explode the memory usage during
the out-of-ssa phase and ultimately allowed compilation to succeed (Jon,
if you're interested, contact me privately and I can give you hints on
finding the right Red Hat BZ).
Jef
