Re: [PATCH] powerpc: POWER7 optimised memcpy using VMX and enhanced prefetch

On Dec 18, 2012, at 10:31 AM, Peter Bergner [off-list ref] =
wrote:

On Tue, 2012-12-18 at 07:28 -0600, Jimi Xenidis wrote:

quoted

On Dec 17, 2012, at 6:26 PM, Peter Bergner [off-list ref] =

wrote:

quoted

quoted

Jimi, are you using an "old" binutils from before my patch that
changed the operand order for these types of instructions?
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  http://sourceware.org/ml/binutils/2009-02/msg00044.html

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Actually, this confused me as well, that embedded has the same =

instruction

quoted

encoding but different mnemonic.

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The mnemonic is the same (ie, dcbtst), and yes, the encoding is the =

same.

All that is different is the accepted operand ordering...and yes, it =

is

very unfortunate the operand ordering is different between embedded =

and

server. :(
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quoted

I was under the impression that the assembler made no instruction =

decisions

quoted

based on CPU.  So your only hint would be that '0b' prefix.
Does AS even see that?

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GAS definitely makes decisions based on CPU (ie, -m<cpu> option).  =

Below is

the GAS code used in recognizing the dcbtst instruction.  This shows =

that

the "server" operand ordering is enabled for POWER4 and later cpus =

while

the "embedded" operand ordering is enabled for pre POWER4 cpus (yes, =

not

exactly a server versus embedded trigger, but that's we agreed on to
mitigate breaking any old asm code out there).
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{"dcbtst",	X(31,246),	X_MASK,      POWER4,	PPCNONE,	=

{RA0, RB, CT}},

{"dcbtst",	X(31,246),	X_MASK,      PPC|PPCVLE, POWER4,	=

{CT, RA0, RB}},

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GAS doesn't look at how the operands are written to try and guess what
operand ordering you are attempting to use.  Rather, it knows what =

ordering

it expects and the values had better match that ordering.
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I agree, but that means it is impossible for the same .S file can be =
compiled but -mcpu=3De500mc and -mcpu=3Dpowerpc?
So either these files have to be Book3S versus Book3E --or-- we use a =
CPP macro to get them right.
FWIW, I prefer the latter which allows more code reuse.

-jx

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Peter
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