Re: 8086 register allocation

Hans-Peter Diettrich <>
Tue, 11 May 2021 03:35:11 +0200

          From comp.compilers

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From: Hans-Peter Diettrich <>
Newsgroups: comp.compilers
Date: Tue, 11 May 2021 03:35:11 +0200
Organization: Compilers Central
References: 21-05-005 21-05-007
Injection-Info:; posting-host=""; logging-data="73561"; mail-complaints-to=""
Keywords: arithmetic, architecture, comment
Posted-Date: 10 May 2021 22:42:28 EDT
In-Reply-To: 21-05-007
Content-Language: de-DE

On 5/10/21 11:49 PM, gah4 wrote:

> It was also designed to have a virtual stack, which would spill to memory
> on overflow, and back on underflow. That sounds nice, but it seems that
> no-one tried to write the interrupt routine before the hardware was built,
> and that it actually isn't possible. It seems that it isn't possible to get some
> of the state bits set, such that it all works like a seamless virtual stack.

How efficient is a virtual stack? Did anybody try to use ordinary
(integral...) registers with interrupt driven spilling?

A stack machine is convenient for calculations. Before the stack
overflows the compiler can save intermediate results, as with any other
architecture of limited register count.

[Normal stack machines have the top few entries in registers and do the
spilling to memory in hardware. The x87 stack has 8 registers, which is
a lot for a stack machine, but the spilling was broken. You can address
into the stack but you can't really use it as a register machine. -John]

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