llvm dev - Jan 2012 - [LLVMdev] Best way to interface with MSVC _ftol2 runtime function for fptoui?

2012/1/18 Jakob Stoklund Olesen <stoklund at
2pi.dk>:
> This should work:
> %1 = call i64 asm "call __ftol2",
"=A,{st},~{dirflag},~{fpsr},~{flags},~{st}" (double %x) nounwind
Thanks Jakob, the ~{st} constraint does the trick. It wasn't clear to
me that "clobbers" means "pops" for x87 registers.

-Joe

2012/1/18 Jakob Stoklund Olesen <stoklund at
2pi.dk>:
> This should work:
> %1 = call i64 asm "call __ftol2",
"=A,{st},~{dirflag},~{fpsr},~{flags},~{st}" (double %x) nounwind
Forgive me for being slow, but what would be the best way to implement
the equivalent of that inline asm as a custom lowering for an
instruction? Can I just create a CallInst and tell it to lower that
instead, or do I need to replicate the functionality manually as DAG
nodes?

-Joe

On Jan 18, 2012, at 8:56 PM, Joe Groff wrote:
> 2012/1/18 Jakob Stoklund Olesen <stoklund at 2pi.dk>:
>> This should work:
>> %1 = call i64 asm "call __ftol2",
"=A,{st},~{dirflag},~{fpsr},~{flags},~{st}" (double %x) nounwind
> 
> Forgive me for being slow, but what would be the best way to implement
> the equivalent of that inline asm as a custom lowering for an
> instruction? Can I just create a CallInst and tell it to lower that
> instead, or do I need to replicate the functionality manually as DAG
> nodes?
On second thought, it might not be the best approach to prodice inline asm
during lowering.

How many of these libcalls do you need to implement? What exactly is the calling
convention? Which registers are clobbered etc.

/jakob