RE: [gentoo-amd64] CFLAGS for Core2?

[Nadav Horesh]

If the machine has the 965 chipset, there is a fair chance that you'll
not be able to boot a 2006.1 CD (I least I couldn't). Please report you
experience.

   Nadav.

-----Original Message-----
From: Jack Lloyd [mailto:lloyd@×××××××××.net] 
Sent: Wednesday, September 20, 2006 22:25
To: gentoo-amd64@l.g.o
Subject: [gentoo-amd64] CFLAGS for Core2?


Tomorrow my new Core 2 workstation should be arriving, and reading
through the 2006.1 amd64 install notes and so forth, the recomended
CFLAGS for EM64T CPUs is -march=nocona. However as that is tuned for
64-bit enabled Netburst rather than Conroe, I'm wondering if anyone
had thoughts on good flags. In particular as (to the extent that I
know anything about microarchitecture), Conroe seems closer to a K8
than a P4, especially with regards to pipeline length and execution
resources, I'm not sure that P4/Netburst tuning is the right thing to
do. But the GCC docs say that -march=k8 enables 3dnow, which Intel
chips don't have. So, right now the "seems likely" options would
be:

-march=k8 -mno-3dnow -msse3
-march=nocona
-march=pentium-m -m64 [saw this suggested in the forums, seems like a
bad idea]

Or can I get away with just something like

-mtune=k8 -msse3   (will this get me 64-bit code?)

To be clear, my main goals here are a) enable generation of all
instructions the CPU has, b) keep GCC from generating 3dnow,etc
instructions, and c) get instruction scheduling that is at least
moderately decent for the uarch I'm using.

Since SSE/SSE2, -mfpmath=sse, and argument passing via registers are
default in 64-bit mode, I suspect the only other options I might try
are -momit-leaf-frame-pointer, -frename-registers, and
-finline-functions.

Ideas?

-Jack
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