x86 Translation question 1

[nimrodpar]

Hi again.

Quick question regarding the translation of some x86 command:

This:
'xor esi, esi'
gets translated into:

   22 | t27 = 32Uto64(0x00000000)
   23 | PUT(rsi) = t27
   24 | t29 = GET:I64(rsi)
   25 | t28 = 64to32(t29)
   26 | t3 = t28
   27 | t31 = GET:I64(rsi)
   28 | t30 = 64to32(t31)
   29 | t2 = t30
   30 | t1 = Xor32(t3,t2)
   31 | PUT(cc_op) = 0x0000000000000013
   32 | t32 = 32Uto64(t1)
   33 | PUT(cc_dep1) = t32
   34 | PUT(cc_dep2) = 0x0000000000000000
   35 | t33 = 32Uto64(t1)
   36 | PUT(rsi) = t33
   37 | PUT(rip) = 0x00000000004098ca

Which is fine except for the first 2 commands that set 0 into rsi (i guess that is what happens, but it's modeled in the rest of the block and kinda makes the actual Xoring wrong)

Any insights as to why this happens?

[zardus]

VEX works in mysterious ways... My guess is that it does this to make it easier for later optimization steps, but we'd have to look at the VEX source to make sure.

[rhelmot]

Also, you can turn on IR optimization, which will hopefully make everything cleaner.