[flang][debug] Avoid redundant debug data generation for derived types. (#124473)
Since https://github.com/llvm/llvm-project/pull/122770, we have seen
that compile time have become extremely slow for cyclic derived types.
In #122770, we made the criteria to cache a derived type very strict. As
a result, some types which are safe to cache were also being
re-generated every type they were required. This increased the compile
time and also the size of the debug info.
Please see the description of PR# 122770. We decided that when
processing `t1`, the type generated for `t2` and `t3` were not safe to
cached. But our algorithm also denied caching to `t1` which as top level
type was safe.
```
type t1
type(t2), pointer :: p1
end type
type t2
type(t3), pointer :: p2
end type
type t3
type(t1), pointer :: p3
end type
```
I have tinkered the check a bit so that top level type is always cached.
To detect a top level type, we use a depth counter that get incremented
before call to `convertRecordType` and decremented after it returns.
After this change, the following
[file](https://github.com/fujitsu/compiler-test-suite/blob/main/Fortran/0394/0394_0031.f90)
from Fujitsu get compiled around 40s which is same as it was before
#122770.
The smaller testcase present in issue #124049 takes less than half a
second. I also added check to make sure that duplicate entries of the
`DICompositeType` are not present in the IR.
Fixes #124049 and #123960.
llvm-project
2e5a5237 - [flang][debug] Avoid redundant debug data generation for derived types. (#124473)
