llvm dev - Jun 2018 - Why doesn't tail recursion elimination work?

Hello.
     Could you please tell me why is not LLVM performing tail recursion
elimination on the
following function:
       int A[10000];

       int MulRedRec(int N) {
           if (N == 0)
               return A[0];
           return A[N] * MulRedRec(N - 1);
       }

     I ask also because, for example, for the following function LLVM is able to
eliminate
tail recursion:
       int FactRec(int N) {
           if (N == 0)
               return 1;
           return N * FactRec(N - 1);
       }

     Looking on the debug information printed by opt I was able to find some
differences
in behavior when opt runs on each of the functions above - I can detail more on
these
differences.

   Thank you very much,
     Alex

Interesting.

gcc does tail recursion elimination on it.

Clang does if you rewrite it like this:

int A[10000];

int MulRedRec(int N) {
    if (N < 0)
        return 1;
    return  A[N] * MulRedRec(N - 1);
}

That's more or less what gcc does by itself.

On Sat, Jun 2, 2018 at 8:32 PM, Alex Susu via llvm-dev <
llvm-dev at lists.llvm.org> wrote:
>   Hello.
>     Could you please tell me why is not LLVM performing tail recursion
> elimination on the following function:
>       int A[10000];
>
>       int MulRedRec(int N) {
>           if (N == 0)
>               return A[0];
>           return A[N] * MulRedRec(N - 1);
>       }
>
>     I ask also because, for example, for the following function LLVM is
> able to eliminate tail recursion:
>       int FactRec(int N) {
>           if (N == 0)
>               return 1;
>           return N * FactRec(N - 1);
>       }
>
>     Looking on the debug information printed by opt I was able to find
> some differences in behavior when opt runs on each of the functions above -
> I can detail more on these differences.
>
>   Thank you very much,
>     Alex
> _______________________________________________
> LLVM Developers mailing list
> llvm-dev at lists.llvm.org
> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>
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