[Flang] [OpenMP] Geometric proliferation of error message lines for each unterminated OpenMP block construct in a Fortran scoping unit.

[thtsikas]

I noticed that multiple OpenMP errors of this kind cause substantial slowdown and excessive error message output.

#!/bin/bash

constructs=(parallel sections workshare paralleldo task master single critical)
for z in $(seq 0 31)
do
    (
        for i in $(seq 0 "${z}")
        do
            echo "!\$omp " "${constructs[$(( i % 8 ))]}"
        done
        echo end
    ) > src.f90
    srcs=$(wc -l src.f90 | cut -d " " -f 1)
#   cat src.f90
    flang-new -c -fopenmp src.f90 |& wc -l > errs.txt
    errs=$(cat errs.txt)
    echo "$srcs" "$errs"
done

[kiranchandramohan]

Hello Themos, Are you requesting for better error messages from the compiler for unterminated block constructs?

[thtsikas]

Yes. At the moment, a 20 line source, can take 20 seconds to produce 835,000+ lines of error messages.

[llvmbot]

@llvm/issue-subscribers-flang-frontend

Author: None (thtsikas)

I noticed that multiple OpenMP errors of this kind cause substantial slowdown and excessive error message output. ``` #!/bin/bash constructs=(parallel sections workshare paralleldo task master single critical) for z in $(seq 0 31) do ( for i in $(seq 0 "${z}") do echo "!\$omp " "${constructs[$(( i % 8 ))]}" done echo end ) > src.f90 srcs=$(wc -l src.f90 | cut -d " " -f 1) # cat src.f90 flang-new -c -fopenmp src.f90 |& wc -l > errs.txt errs=$(cat errs.txt) echo "$srcs" "$errs" done ```

[kiranchandramohan]

Does https://github.com/llvm/llvm-project/pull/90480 make it better?

[thtsikas]

Sadly, no. It's not the quality of the messages that is the problem in this Issue. It is the quantity of them and the cpu time expended.

[kiranchandramohan]

The parser is reporting the scope of the error. As the nesting of the scope increases there are more messages in the error message for the nested scopes. This can be reproduced without OpenMP in the following example.

block
block
block
block
block
block
block
block
block
block
end

[kiranchandramohan]

Reopened since the patch does not fix this issue. I missed removing the fixes tag before submitting.