[llvm-dev] Help on understanding assume shape array processing and array descriptors in LLVM IR

[Venkataramanan Kumar via llvm-dev]

Hi Eugene,

On 25 April 2018 at 22:39, Epshteyn, Eugene via llvm-dev <
llvm-dev at lists.llvm.org> wrote:

> Hello,
>
>
>
> I believe these descriptors are specific to flang, not to LLVM.  You
> should probably ask your question on flang-dev list.
>
>
>
> Thank you,
>
>
>
> --Eugene
>

Thanks I will check with flang dev list.

>
>
> *From:* llvm-dev [mailto:llvm-dev-bounces at lists.llvm.org] *On Behalf Of *Venkataramanan
> Kumar via llvm-dev
> *Sent:* Wednesday, April 25, 2018 8:44 AM
> *To:* llvm-dev at lists.llvm.org
> *Subject:* [llvm-dev] Help on understanding assume shape array processing
> and array descriptors in LLVM IR
>
>
>
> Hi,
>
> I am trying to understand how assume shaped arrays are received and
> processed in LLVM IR.  I am using "flang" for my front end.
>
> There seems to be an array descriptor received as implicit argument
> for every assume shaped array.
>
> For my test routine:
>
> ---snip--
>    SUBROUTINE test(a,b,Li,Lj,Istr,Iend,Jstr,Jend)
>      INTEGER, INTENT(IN) :: Li,Lj
>      INTEGER, INTENT(IN) :: Istr, Iend, Jstr,Jend
>      INTEGER :: i, j
>      REAL*8, INTENT(INOUT)   :: a(Li:,Lj:)
>      REAL*8, INTENT(IN)      :: b(Li:,Lj:)
> --snip--
>
> I got the below LLVM IR, the parameters received.
>
> --snip--
> ; Function Attrs: norecurse nounwind
> define void @test_(i64* noalias nocapture %a, i64* noalias nocapture
> readonly %b, i64* noalias nocapture readonly %li, i64* noalias
> nocapture readonly %lj, i64* noalias nocapture readonly %istr, i64*
> noalias nocapture readonly %iend, i64* noalias nocapture readonly
> %jstr, i64* noalias nocapture readonly %jend, i64* noalias nocapture
> readonly %"a$sd", i64* noalias nocapture readonly %"b$sd")
> local_unnamed_addr #0 !dbg !5 {
> --snip--
>
> Here "a$sd" and "b$sd" looks like array descriptors and received as
> implicit parameters.
>
> I found this article which explains how gfortran implements:
> http://thinkingeek.com/2017/01/14/gfortran-array-descriptor/
>
> Can Someone throw some light on LLVM's array descriptors and how they
> are processed ?
>
> regards,
> Venkat.
>
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>
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