LDC2 win64 calling convention

[kinke]

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).