On 4/12/2016 4:29 PM, Marco Leise wrote:
Am Tue, 12 Apr 2016 13:22:12 -0700
schrieb Walter Bright <newshou...@digitalmars.com>:
On 4/12/2016 9:53 AM, Marco Leise wrote:
LDC implements InlineAsm_X86_Any (DMD style asm), so
core.cpuid works. GDC is the only compiler that does not
implement it. We agree that core.cpuid should provide this
information, but what we have now - core.cpuid in a mix with
GDC's lack of DMD style asm - does not work in practice for
the years to come.
Years? Anyone who needs core.cpuid could translate it to GDC's inline asm style
in an hour or so. It could even be simply written separately in GAS and linked
in. Since this has not been done, I can only conclude that core.cpuid has not
been an actual blocker.
You mean it is ok, if I duplicated most of the asm in there
and created a pull request ?
It's Boost licensed, and Boost licensed code can be shipped with GPL'd code as
far as I know.
"mulq %[y]"
: "=a" tmp.lo, "=d" tmp.hi : "a" x, [y] "rm" y;
I don't see anything elegant about those lines, starting with "mulq" is not in
any of the AMD or Intel CPU manuals. The assembler should notice that 'y' is a
ulong and select the 64 bit version of the MUL opcode automatically.
I can see nothing to recommend the:
"=a" tmp.lo
syntax. How about something comprehensible like "tmp.lo = EAX"? I bet people
could even figure that out without consulting stackoverflow! :-)
I have no idea what:
"a" x
and:
[y] "rm" y
mean, nor why the ":" appears sometimes and the "," other times. It does look
like it was designed by the same guy who invented TECO macros:
https://www.reddit.com/r/programming/comments/4e07lo/last_night_in_a_fit_of_boredom_far_away_from_my/d1xlbh7
but that's not much of a compliment.
In practice GDC will just replace the invokation with a single
'mul' instruction while DMD will emit a call to this 18
instructions long function. Now you keep telling me extended
assembly is a step backwards. :)
DMD version:
DblWord bigMul(ulong x, ulong y) {
naked asm {
mov RAX,RDI;
mul RSI;
ret;
}
}
GCC's inline assembler apparently has no knowledge of what
the opcodes actually do.
Agreed.
This is the basis of my assertion it is a step backwards. Granted, it has some
nice capability as you've demonstrated. But it sure makes you suffer to get it.
