[LLVMdev] __float128 (f128) calling convention bug on x86_64

[Chih-hung Hsieh]

To be clear, what I plan to change is for the following C code:

  long double foo1(long double x) { return x * x; }
  long double _Complex foo2(long double _Complex x) { return x * x; }

on x86_64, when long double is mapped to f128, current LLVM IR:

   define x86_fp80 @foo1(fp128 %x)
   define { x86_fp80, x86_fp80 } @foo2({ fp128, fp128 }* byval align 16 %x)

to be changed to match gcc, and new LLVM IR:

  define fp128 @foo1(fp128 %x)
  define void @foo2({ fp128, fp128 }* noalias sret %agg.result, { fp128,
fp128 }* byval align 16 %x)

I added a long double _Complex bug at
https://llvm.org/bugs/show_bug.cgi?id=24111



On Wed, Jul 15, 2015 at 9:42 AM, David Majnemer <david.majnemer at gmail.com>
wrote:

>
>
> On Wed, Jul 15, 2015 at 9:01 AM, Reid Kleckner <rnk at google.com> wrote:
>
>> On Mon, Jul 13, 2015 at 12:33 PM, Chih-hung Hsieh <chh at google.com> wrote:
>>>
>>> I found that long double complex (with two f128 values) also have
>>> calling convention compatibility problem with gcc and can be fixed
>>> similarly.
>>> My current patch does change quite a few places in type legalizing pass
>>> and some other optimizations related to f128 or i128 values. A few changes
>>> in the softening of floating point types to keep some f128 typed IR and
>>> convert some f128 opcode to library function calls.
>>>
>>> Has anyone tried this approach or have other solution?
>>>
>>
>> It sounds like you're on the right track for the low-level part of this.
>>
>> The responsibility of matching platform ABI calling conventions is sort
>> of split across clang and LLVM. I think the way to get the calling
>> convention right is to change Clang to use x86_fp80 as the LLVM type for
>> parameter and return types, with some extra coercions inserted before calls
>> and in function prologues.
>>
>> The mangling will need a separate change as it doesn't look at LLVM IR.
>>
>
> I think you'll want to implement "useFloat128ManglingForLongDouble" for
> the mangling change.
>
>
>>
>> _______________________________________________
>> LLVM Developers mailing list
>> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
>> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
>>
>>
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.llvm.org/pipermail/llvm-dev/attachments/20150715/86888d8a/attachment.html>