[LLVMdev] How to disable register allocate optimization?

[Akira Hatanaka]

It looks like you are not using the right overloaded version of function
BuildMI defined in MachineInstrBuilder.h.

The register operand added to instruction sb should be a use, not a def
operand. So this function should be called,

BuildMI(BB, dl, TII->get(Mips::SB)).addReg(tmpReg1)

instead of

BuildMI(BB, dl, TII->get(Mips::SB), tmpReg1)



On Sat, Jul 21, 2012 at 11:41 AM, Yang Yang <geraint0923 at gmail.com> wrote:

> Hi everyone,
>
> I am trying to expand one instruction into multiple instructions on MIPS.
> For example, I try to expand:
>         sh      src, imm(dst)
> into:
> (1)     sb      src, imm(dst)
> (2)     srl     reg0, src, 8
> (3)     sb      reg0, (imm+1)(dst)
> Here, reg0 are created with createVirtualRegister.
>
> However, instr(2) will not be emitted because reg0 is useless before reg0
> is defined in instr(3), it is wrong!
> So how to prevent the expansion from being optimized?
> Is there any method to disable register allocate optimization?
>
> Thanks in advance.
>
> Yang
>
>
>
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