[LLVMdev] Problems expanding fcmp to a libcall

Evan Cheng evan.cheng at apple.com
Tue Jun 24 14:54:39 PDT 2008

On Jun 23, 2008, at 5:35 AM, Richard Osborne wrote:

> I'm trying to write a backend for a target with no hardware floating
> point support. I've added a single i32 register class. I'm wanting all
> floating point operations to be lowered to library function calls. For
> the most part LLVM seems to get this right. For example
> define double @div(double %a, double %b) {
> %result = fdiv double %a, %b
> ret double %result
> }
> is expanded to a ISD::CALL of __divdf3 which is then lowered via the
> LowerOperation hook of my backend.
> However I run into problems with fcmp. With the following code:
> define i1 @fmp(double %a) {
> %result = fcmp uno double %a, 0.000000e+00
> ret i1 %result
> }
> the fcmp is expanded to the a call to __unorddf2 which is then
> lowered via the LowerOperation hook of my backend. However for some  
> reason
> there remains a ISD::CALL node with __unorddf2 in the DAG after
> legalization. This
> then causes selection to fail with
> Cannot yet select: 0x13b7cc0: i32,i32,ch = call 0x13b76e0, 0x13b7800,
> 0x13b7800, 0x13b7800, 0x13b77a0, 0x13b78f0, 0x13b79a0, 0x13b80d0,
> 0x13b7a00, 0x13b78f0, 0x13b79a0, 0x13b80d0, 0x13b7a00
> Are there any additional steps I need to take in my target, or could
> this be a bug in the Legalization phase?

This sounds like a bug in your target. Why not custom lower the f32  
setcc nodes directly to the desired target nodes rather than doing  
this  two stage lowering?


> Regards,
> Richard Osborne
> _______________________________________________
> LLVM Developers mailing list
> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev

More information about the llvm-dev mailing list