[SYSTEMDS-2949] Function return on same calls

• Type: Bug
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Affects Version/s: SystemDS 2.0, SystemDS 2.1
• Fix Version/s: SystemDS 2.1
• Component/s: Compiler
• Labels: Compiler
• Assignee: Matthias Boehm
• Reporter: Sebastian Baunsgaard
• Created: 26/Apr/21 10:05
• Updated: 12/May/21 21:11
• Resolved: 12/May/21 21:11

Description

Currently the builtin functions express wired null pointer behaviour if one execute a builtin function more than once with the same arguments, and use the output in side an operation directly

example:

```R
x = func(a,b) - c
y = func(a,b) - d
```
here the secound execution of func crash with a null pointer

currently the workaround is to do:

```R
r = func(a,b)
x = r - c
y = r - d
```

But our compiler should learn how to do this itself.

Note that if the function is called purely then there is no issues:

```R
x = func(a,b)
y = func(a,b)
x = x - c
x = y - d
```

Bug Found in https://github.com/apache/systemds/pull/1240

use that as code base for example:
https://raw.githubusercontent.com/apache/systemds/988d8ef06f0e29ed8490b68f6ad60e00cc1a654e/scripts/builtin/garch.dml