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Subject: Re: gcc -O3 and register usage
From: Felipe Alfaro Solana <felipe_alfaro@linuxmail.org>
To: "J.A. Magallon" <jamagallon@able.es>
Cc: Lista Linux-Kernel <linux-kernel@vger.kernel.org>
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Date: Tue, 19 Aug 2003 12:17:19 +0200
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On Tue, 2003-08-19 at 02:15, J.A. Magallon wrote:

> Does this mean that since PentiumPro gcc has one other register (%dl)
> available, and it uses it only at -O3 ?

AFAIK, the EDX 32-bit register is splitted in two 16-bit halves, being
the least significant half called DX which, at the sime time, is
splitted in two 8-bit halves of which the most significant is called DH,
while the least significant is called DL.

So, DL is not a new register, but the least significant 8-bits from the
EDX CPU register.