Andi Kleen wrote:
On Mon, Jan 12, 2009 at 11:02:17AM -0800, Linus Torvalds wrote:
Something at the back of my mind said "aliasing".
$ gcc linus.c -O2 -S ; grep subl linus.s
subl $1624, %esp
$ gcc linus.c -O2 -S -fno-strict-aliasing; grep subl linus.s
subl $824, %esp
That's with 4.3.2.
Interesting.
Nonsensical, but interesting.
What I find nonsensical is that -fno-strict-aliasing generates
better code here. Normally one would expect the compiler seeing
more aliases with that option and then be more conservative
regarding any sharing. But it seems to be the other way round
here.
For this to be convolved with aliasing *AT ALL* indicates this is done
incorrectly.
This is about storage allocation, not aliases. Storage allocation only
depends on lifetime.
-hpa
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