[PATCH] D75326: [entry values] X86: Describe effects of MOV{8,16}ri (PR45053)

[Djordje Todorovic via Phabricator via llvm-commits]

djtodoro added inline comments.


================
Comment at: llvm/lib/Target/X86/X86InstrInfo.cpp:7795
     // 64-bit parameters, so we need to consider super-registers.
     if (!TRI->isSuperRegisterEq(MI.getOperand(0).getReg(), Reg))
       return None;
----------------
dstenb wrote:
> At least when I tried this out on a 8th generation i7, it seems that MOV8ri and MOV16ri do not modify the upper bits in super-registers.
> 
> ```
>         movl    $287454020, %edi        # imm = 0x11223344                                                                                                                                                                                                                                                                     
>         mov     $21862, %di             # imm = 0x5566
>         movb    $119, %dil              # imm = 0x77
>         callq   call
> ```
> 
> That produces the value 0x11225577.
> 
> In this test case we try to describe:
> 
> ```
>     renamable $rsi = LEA64r $rip, 1, $noreg, @.str, $noreg, debug-location !51
>     renamable $si = MOV16ri 2112
> ```
> 
> As `Reg` is a 32-bit register, I think we want to return something like this for the MOV16ri instruction:
> 
> ```
> ParamLoadedValue(Reg, (DW_OP_constu, 0xFFFF0000, DW_OP_and, DW_OP_constu, MI.getOperand(1).getImm(), DW_OP_or))
> ```
> 
> 
>At least when I tried this out on a 8th generation i7, it seems that MOV8ri and MOV16ri do not modify the upper bits in super-registers.
I have not tried debugging it, but I guess this would result a wrong value printed within debugger, and we need this:

>As Reg is a 32-bit register, I think we want to return something like this for the MOV16ri instruction:
>ParamLoadedValue(Reg, (DW_OP_constu, 0xFFFF0000, DW_OP_and, DW_OP_constu, MI.getOperand(1).getImm(), DW_OP_or))

If that is the case, I agree with that. So the `X86::MOV8ri` and `X86::MOV16ri`should be handled as a special case here.


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