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Hi Fellows, I’ve recently encountered a problem with X86 segment registers. I created a new calling convention and for some purposes I have to use a segment register for one of the argument passed by the caller. I found out that in X86RegisterInfo.td, SEGMENT_REG was defined there, and I directly grabbed the one I need into my calling convention in X86CallingConv.td. However, I got an error while I was trying to codegen a function with my specific calling convention. The error is "Cannot emit physreg copy instruction” which is in llvm::X86InstrInfo::co...

Hello Matthias, On 28 July 2017 at 04:13, Matthias Braun <mbraun at apple.com> wrote: > It's not that hard in principle: > - A register class is a set of registers. > - Virtual Registers have a register class assigned. > - If you have register constraints (like x86 8bit operations only work on > al,ah,etc.) then you have to create a new register class to express that.