Re: Why Plan 9 C compilers don't have asm("")

From: Richard Henderson (
Date: Sat Jul 21 2001 - 17:10:55 EST

On Wed, Jul 04, 2001 at 05:22:44PM +0000, Linus Torvalds wrote:
> [ And yes, I know there are optimizing linkers for the alpha around that
> improve this and notice when they don't need to change GP and can do a
> straight branch etc. I don't think GNU ld _still_ does that, but who
> knows.

GNU ld does it with the "-relax" flag.

> Even the "good" Digital compilers tended to nop out unnecessary
> instructions rather than remove them, causing more icache pressure on
> a CPU that was already famous for needing tons of icache ]

But you're absolutely right about the nopping -- removing the nops would
require debug info and EH info to be re-coded. The later being a matter
of correctness. This is a bit nastier than I ever cared to deal with.

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