On Wed, 21 Mar 2012, Tijl Coosemans wrote:
On Tuesday 20 March 2012 19:56:14 John Baldwin wrote:
On Tuesday, March 20, 2012 10:19:07 am Tijl Coosemans wrote:
...
No, on i386 bswap64 with a variable argument currently expands to two
bswap instructions. With your change it would be many shifts and logical
operations. The _gen variants are more like fallback implementations.
If bswapNN cannot be implemented directly it is split up. If those
smaller problems can be implemented directly, good, if not split it up
again and so on.
Oh, I now parse the comment in __bswap64_var() correctly. That's fugly.
Still, it seems that if I keep the patch to port this to ia64 (so it
can do constants as constants), then it will need to use this approach
since it won't have the i386 problem (in its case the _gen variants
are only used for constants).
Maybe name them _const then as on other architectures.
But we hoped to to use the "generic" version on all arches, with only
1 definition for it, and nothing MD except possibly the "var" version.
The "constant" version was renamed because it isn't limited to
constants. I think it was changed to call the general version (above
the "generic" version) after that, since it would have made no sense for
the "constant" version to call a non-"constant" version. The "generic"
version isn't really generic, since it only works for parameters without
side effects. This is arranged by the "var" versions copying the parameters
to non-volatile variables and then applying either the "generic" version or
asm.
Bruce
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