On Wednesday, 28 November 2018 at 21:58:16 UTC, kinke wrote:
You're not using naked asm; this entails a prologue (spilling
the params to stack etc.). Additionally, LDC doesn't really
like accessing params and locals in DMD-style inline asm, see
https://github.com/ldc-developers/ldc/issues/2854.
You can check the final asm trivially online, e.g.,
https://run.dlang.io/is/e0c2Ly (click the ASM button). You'll
see that your params are in R8, RDX and RCX (reversed order as
mentioned earlier).
Hi again.
I just tried a new debugger: x64dbg. I really like it, it is not
the bloatware I got used to nowadays.
It turns out that LDC2's parameter/register handling is really
clever:
- Register saving/restoring: fully automatic. It analyzes my asm
and saves/restores only those regs I overwrite.
- Parameters: Reversed Microsoft x64 calling convention, just as
you said. Parameters in the registers will be 'spilled' onto the
stack no matter if I'm using them by their names or by the
register. Maybe this is not too clever but as I can use the
params by their name from anywhere, it can make my code nicer.
- Must not use the "ret" instruction because it will take it
literally and will skip the auto-generated exit code.
In conclusion: Maybe LDC2 generates a lot of extra code, but I
always make longer asm routines, so it's not a problem for me at
all while it helps me a lot.
