Messages in this thread | | | Date | Mon, 12 Jan 2009 11:22:56 -0800 | From | "H. Peter Anvin" <> | Subject | Re: gcc inlining heuristics was Re: [PATCH -v7][RFC]: mutex: implement adaptive spinning |
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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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