Do you want to make LDC2 recognize core.checkedint functions and implement them efficiently reading the overflow/carry flags of the CPU?

Bye,
bearophile

On 1 Nov 2014, at 1:58, bearophile via digitalmars-d-ldc wrote:
> Do you want to make LDC2 recognize core.checkedint functions and implement them efficiently reading the overflow/carry flags of the CPU?

Sure, it maps very directly to the corresponding LLVM intrinsics (conditionally setting the by-ref parameter has to be done in a small wrapper, though). Pull request are very welcome. ;)

David

I'm not terribly interested in preparing a PR for this, but I believe the code should be something like this (untested):

ldc/src/core/checkedint.d:

uint mulu(uint x, uint y, ref bool overflow)
{
+ version (LDC)
+ {
+     auto res = llvm_umul_with_overflow(x, y);
+     overflow |= res.overflow;
+     return res.result;
+ }
+ else
+ {
      ulong r = ulong(x) * ulong(y);
      if (r > uint.max)
          overflow = true;
      return cast(uint)r;
+ }
}

Rinse and repeat with:
llvm_uadd_with_overflow, llvm_sadd_with_overflow, llvm_usub_with_overflow, llvm_ssub_with_overflow, llvm_smul_with_overflow.

safety0ff:

> Rinse and repeat with:
> llvm_uadd_with_overflow, llvm_sadd_with_overflow, llvm_usub_with_overflow, llvm_ssub_with_overflow, llvm_smul_with_overflow.

Good.
Is it 100% guaranteed ldc2 will inline this function?

Bye,
bearophile

On Saturday, 1 November 2014 at 18:06:41 UTC, bearophile wrote:
> safety0ff:
>
>> Rinse and repeat with:
>> llvm_uadd_with_overflow, llvm_sadd_with_overflow, llvm_usub_with_overflow, llvm_ssub_with_overflow, llvm_smul_with_overflow.
>
> Good.
> Is it 100% guaranteed ldc2 will inline this function?
>
> Bye,
> bearophile

They're intrinsics:
https://github.com/ldc-developers/druntime/blob/ldc/src/ldc/intrinsics.di#L462

safety0ff:

> They're intrinsics:
> https://github.com/ldc-developers/druntime/blob/ldc/src/ldc/intrinsics.di#L462

Sorry, I meant the functions like mulu, etc.

Bye,
bearophile

On Saturday, 1 November 2014 at 04:04:48 UTC, David Nadlinger via digitalmars-d-ldc wrote:
> On 1 Nov 2014, at 1:58, bearophile via digitalmars-d-ldc wrote:
>> Do you want to make LDC2 recognize core.checkedint functions and implement them efficiently reading the overflow/carry flags of the CPU?
>
> Sure, it maps very directly to the corresponding LLVM intrinsics (conditionally setting the by-ref parameter has to be done in a small wrapper, though). Pull request are very welcome. ;)
>
> David

See https://github.com/ldc-developers/ldc/pull/772

Regards,
Kai