Improper return register selection for x86 xmm0

[whitequark]

Version and Platform (required):

• Binary Ninja Version: 4.2.6039-dev Personal (d2968e13)

Bug Description:
This basic block seems to be decompiled wrong, with temp[0] being introduced and going nowhere:

Steps To Reproduce:
Please provide all steps required to reproduce the behavior:

1. Open libDly_DelayCalculator.so
2. Go to 0x00074ed2
3. Rotate through views

Expected Behavior:
An arithmetic expression is assembled from LLIL fragments and returned.

Binary:
libDly_DelayCalculator.so.zip

[whitequark]

For context, the function should be computing something like this:

(with added fluff around it)

[xusheng6]

I have renamed the issue title because it seems to be happening during MLIL->HLIL translation. Though I do not yet know what is causing it. Will need someone else to look into it

[whitequark]

Ah, I've made some invalid assumptions then. Thanks for triaging this!

[emesare]

This is an issue with return register selection. The function returns with zmm0 but the selected return register was rax.

Until this is fixed, setting the return type to a double, or adjusting the return register in "Edit Function Properties" will fix the HLIL.

[whitequark]

Thanks!

[plafosse]

In many cases is almost impossible to tell if the return value should be in rax or xmm0 however in this case as there are no uses of rax the correct choice should be obvious.