Am 15.03.19 um 11:32 schrieb J. Gareth Moreton:
Hi everyone,
Sorry for the slightly long-winded title. This was something I've been
working on for the past few weeks to allow the use of "inline" with
certain x86 assembler routines, subject to restrictions for safety
reasons. I have successfully written code that implements this support
while ensuring it doesn't affect platforms with a different assembly
languages. Regression tests have passed, as have some new tests, some
of which test modified RTL assembler functions that have had "inline"
added to their list of directives.
As said before, I have a lot of concerns against this as it opens a can
of worms hard to handle:
* using inline assembler is always the worst solution to do something,
it normally means either:
- the compiler misses a certain feature
- the compiler is generating bad code
* intrinsics provide a much better way to achieve exactly what this
approach aims at:
- they enable the use of all registers as the compiler does register
allocation
- constraints on instructions (like a certain operand needs to be a
constant) can be easily forced
Is there any advantage over intrinsics, I missed so far?
There was a previous concern about it breaking too much and it being
impossible to implement on all platforms - the latter point may be true,
but through the careful use of virtual methods within the compiler, it
should be possible to extend the inline support one platform at a time
without breaking the others.
All the details, including a PDF specification that explains the design
and implementation choices, a couple of existing tests that touch on the
functionality, along with any new tests, limitations or problems found,
can be found here: https://bugs.freepascal.org/view.php?id=35232
I hope it proves to be insightful and useful.
Gareth aka. Kit
P.S. Though this feature can be used for implementing intrinsics, it is
not a direct replacement for them because instructions like SHUFPS
cannot be flexibly encoded due to its immediate operand (i.e. it has to
be a raw number... it can't take its value from a parameter).
Well, with intrinsics, this can be easily done.
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