[llvm-dev] MIR instruction size
Matthias Braun via llvm-dev
llvm-dev at lists.llvm.org
Thu Apr 20 14:55:28 PDT 2017
X86 instructions are variable size. Depending on which registers are allocated or what sized immediate an instruction variant takes you may need additional rex/rex.w prefixes immediate bytes etc.
There is no API today that would answer that question, and even if there were it would be a dangerous API as later passes could change the size just by swapping some registers.
> On Apr 20, 2017, at 11:28 AM, Ilya Skapenko via llvm-dev <llvm-dev at lists.llvm.org> wrote:
> Is there any common way to determine a size of MIR instruction? I've tried both: MachineInstr::getDesc().getSize() and TargetInstrInfo::getInstSizeInBytes(I), and unfortunately, both interfaces can't determine instruction sizes for x86_64, though they could do it for arm architecture.
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