[X86 MIR] Get memory address read in PUSH64rmm

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1

Hi there,

I’m working on an MIR transformation for X86, and I need to get all memory addresses accessed by any X86 instruction. I’ve been using MachineInstr::memoperands() to iterate over all MachineMemOperands and using X86II::getMemoryOperandNo() and X86II::getOperandBias() to get the index of the base_reg MachineOperand. This seems to work fine for most instructions, until I saw the following instruction:

X86: pushq 0x20(%rbx)

MIR: PUSH64rmm renamable $rbx, 1, $noreg, 32, $noreg, implicit-def $rsp, implicit $rsp

For the above MachineInstr, MachineInstr::getNumMemOperands() returns 0: there’s no MachineMemOperands. However, this instruction clearly accesses the memory address specified by [%rbx + 0x20]. I wonder how I can get the memory addresses for instructions like this?

Thanks!
Yuanfeng Peng

2

Hello

Well, I'm afraid I had to disappoint you. The memory operands are
always optional, you cannot rely on their presence. And it's perfectly
fine to have instructions that access memory but do not have memory
operands.