[LLVMdev] Improving i128 division on x86_64

[Paweł Bylica]

Hi LLVM,

I think the potential of divq instruction is not fully exploited by X86
target.

The following IR can be lowered to one divq instruction:
define i64 @div128by64lo(i128 %d, i64 %n) nounwind readnone {
  %m = zext i64 %n to i128
  %q = udiv i128 %d, %m
  %q.l = trunc i128 %q to i64
  ret i64 %q.l
}

And that one can be 2 divq instructions:
define i128 @div128by64full(i128 %d, i64 %n) nounwind readnone {
  %m = zext i64 %n to i128
  %q = udiv i128 %d, %m
  ret i128 %q
}

In current implementation, everywhere where i128 type shows up codegen
generates a call to  __udivti3 builtin function.

Am I missing something?
- Paweł
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.llvm.org/pipermail/llvm-dev/attachments/20150514/9966e606/attachment.html>