[LLVMbugs] [Bug 15046] New: incorrect signature for soft float routines

[bugzilla-daemon at llvm.org]

http://llvm.org/bugs/show_bug.cgi?id=15046

             Bug #: 15046
           Summary: incorrect signature for soft float routines
           Product: tools
           Version: trunk
          Platform: PC
        OS/Version: Linux
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: llc
        AssignedTo: unassignedbugs at nondot.org
        ReportedBy: rkotler at mips.com
                CC: llvmbugs at cs.uiuc.edu
    Classification: Unclassified


hat happens here is that the code that is doing the "softening", generates a
libcall

On closer inspection, llvm is doing half of this correctly.

The signature for the soft float function for extending a float to double is of
the form:

i64 xxx_extendsfdf2(float);

But it should be

i64 xxx_extendsfdf2(i32)

This particular paradigm is duplicated many times in the the float type
lowering.

I'm not sure exactly how to change this and what effect if any that it might
have.

thoughts?

In my case for mips16, it's important that I know the proper function
signature, otherwise I'll generate an unnecessary helper function call.

tia.

Reed

On 01/20/2013 06:28 AM, Reed Kotler wrote:
> I'm implementing this unusual gcc form of mips16 hard float.
>
> I ran into one unexpected wrinkle. It effects efficiency as opposed to
> correctness but I'd like to figure out the best way to resolve it.
>
> The signatures for the libcall routines have floating point arguments
> in  at least some situations. I have not fully examined
> if it's all of them. So in callinfo while I'm lowering the call, the
> first argument for example will appear to be a float.
>
> For sure in the following situation:
>
> float f;
> ...
> printf("%f \n", f);
>
> So it generates a libcall to widen f to double.
>
> long int XXX_extendsfdf2(float);
>
> The problem for me is that the parameter should be int since this is a
> soft float routine. Probably nobody ever looks at this argument type in
> this situation.
>
> So I think this should look like:
> long int XXX_extendsfdf2(int);
>
> In my case the routine is called __mips16_extendsfdf2 .
>
> When I see the first parameter as float, I think that I need to generate
> a mips16 helper function. This is because in the abi that parameter
> would be passed in a floating point argument register but this is not
> possible in mips16 mode since there are no floating point instructions.
>
> For interoperability between mips16 and mips32, when I see an external
> call, I don't know if it's mips16 or mips32, so I automatically must
> generate a helper function so that the call works correctly whether the
> extern is in a module compiled as mips16 or mips32.
>
> What I was not expecting is to see such a signature from a routine which
> is already a routine generated for soft float.
>
> So I'm generating an unneeded call to a helper function.
>
> I could try and filter it out based on the name of the routine being
> called but it seems that this is just the result of a mistake in target
> independent code.

-- 
Configure bugmail: http://llvm.org/bugs/userprefs.cgi?tab=email
------- You are receiving this mail because: -------
You are on the CC list for the bug.