[LLVMdev] FPU cannot be compatible with -soft-float code on mips by llc

[Daniel Sanders]

The –soft-float option won't be necessary once FP16_TO_FP and FP_TO_FP16 are set to 'Expand' as Tim suggested. This will cause LLVM to replace these nodes with a libcall while everything else continues to use the hardware support.

I believe you need to add these calls to MipsISelLowering.cpp:
setOperationAction(ISD::FP16_TO_FP, MVT::f32, Expand); // Conversion from half -> float
setOperationAction(ISD::FP_TO_FP16, MVT::f32, Expand); // Conversion from float -> half
setOperationAction(ISD::FP16_TO_FP, MVT::f64, Expand); // Conversion from half -> double
setOperationAction(ISD::FP_TO_FP16, MVT::f64, Expand); // Conversion from double -> half

From: llvmdev-bounces at cs.uiuc.edu [mailto:llvmdev-bounces at cs.uiuc.edu] On Behalf Of ???
Sent: 28 July 2014 09:21
To: Jim Grosbach
Cc: llvmdev at cs.uiuc.edu
Subject: Re: [LLVMdev] FPU cannot be compatible with -soft-float code on mips by llc

Hi Jim,
    X86 and ARM have the assembly instruction convert float to half/covert half to float, so they need not to call libcall, but MIPS have not.  So we must add -soft-float option. The terrible thing is all function will be using soft, not FPU (hard).

Cheers,
Robin

________________________________
liuyalong.email at gmail.com<mailto:liuyalong.email at gmail.com>

From: Jim Grosbach<mailto:grosbach at apple.com>
Date: 2014-07-25 10<tel:2014-07-25%C2%A010>:50
To: 刘亚龙<mailto:liuyalong.email at gmail.com>
CC: llvmdev<mailto:llvmdev at cs.uiuc.edu>
Subject: Re: [LLVMdev] FPU cannot be compatible with -soft-float code on mips by llc
Hi Robin,

It sounds like you want to support half (f16 in LLVM terms) as a storage only interchange format. AArch64 and X86 (among others) do the same thing. You shouldn’t need the “-soft-float” option or anything of that nature at all. That, as you’ve found, disables all hard float operations. There’s been some recent cleanup in how this is handled in LLVM that should help guide you in what the Mips backend needs to do. In particular, Tim Northover’s recent patch, r213374.

Regards,
  Jim

On Jul 24, 2014, at 6:32 PM, 刘亚龙 <liuyalong.email at gmail.com<mailto:liuyalong.email at gmail.com>> wrote:

Hi all,
    -soft-float can not be rightly use by llc. All float function operation will call soft float, but not hard.
    My mips device cannot support half float type, so I hack the llvm, and add soft half float and add -soft-float option.
    I add the function define for __gnu_f2h_ieee() and __gnu_h2f_ieee (), and it can call the soft half float.
    However, all the others function about float also call the soft float, how I do make only __gnu_f2h_ieee() use soft float, other use hard float???

    Thank you all !!

Cheers,
    Robin
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