Port to flang and F90 compliance of madgraph fortran codebase

[valassi]

Hi @oliviermattelaer , as part of PR #801 for porting to LUMI with AMD GPUs, I am experimenting with flang as a fortran compiler.

(I am using flang because I get several issues with gfortran... linking c++, fortran and hip code seems rather complex, see for instance #802).

I managed to use the /opt/rocm/llvm/bin/flang compiler for the standalone code, where there is very limited fortran. But the moment I try building madevent, it's just a catastrophe (see below*).

I guess that this flang does not support F77, or at least all the legacy f77 stuff in madevent. This is not a blocker per se, but something to keep in mind. I think flang looks like the future of fortran compilers. Maybe more features will be added, maybe not.

In my understanding (I may be wrong), the flang I am testing is the "new flang" aka f18, a rewrite from the grounds up of the flang compiler in c++. See https://github.com/llvm/llvm-project/blob/main/flang/README.md#getting-started. The features supported are here I think https://github.com/llvm/llvm-project/blob/main/flang/docs/Extensions.md. (For comparison, the "old flang" or "classic flang" is here https://github.com/flang-compiler/flang).

I am trying to check if I can do anything with it, but I guess on LUMI we need to go back to gfortran and massage all link issues. (@Jooorgen in case you read this, any suggestion on what combination to use? thanks)

Andrea

PS *One example, for myamp

ccache /opt/rocm-5.2.3/llvm/bin/flang -w -fPIC -O3 -ffast-math -fbounds-check -ffixed-line-length-132 -w -cpp -c myamp.f -I../../Source/ -I../../Source/PDF/g\
ammaUPC
F90-S-0023-Syntax error - unbalanced parentheses (../../Source/genps.inc: 9)
F90-S-0087-Non-constant expression where constant expression required (../../Source/genps.inc: 25)
F90-S-0087-Non-constant expression where constant expression required (../../Source/genps.inc: 27)
F90-S-0034-Syntax error at or near end of line (../../Source/run.inc: 10)
F90-S-0023-Syntax error - unbalanced parentheses (../../Source/run.inc: 55)
F90-S-0023-Syntax error - unbalanced parentheses (../../Source/run.inc: 56)
F90-S-0023-Syntax error - unbalanced parentheses (myamp.f: 83)
F90-S-0023-Syntax error - unbalanced parentheses (myamp.f: 117)
F90-S-0023-Syntax error - unbalanced parentheses (myamp.f: 132)
F90-S-0023-Syntax error - unbalanced parentheses (myamp.f: 152)
F90-S-0038-Symbol, mue_over_fixed_ren_scale, has not been explicitly declared (myamp.f)
F90-S-0038-Symbol, fixed_fac_scale2fixed_couplings, has not been explicitly declared (myamp.f)
F90-S-0038-Symbol, hmdynamical_scale_choice, has not been explicitly declared (myamp.f)
F90-S-0038-Symbol, ievo_eva, has not been explicitly declared (myamp.f)
F90-S-0038-Symbol, n_pdfrw, has not been explicitly declared (myamp.f)
F90-S-0038-Symbol, i_pdgpdf, has not been explicitly declared (myamp.f)
F90-S-0038-Symbol, s_xpdf, has not been explicitly declared (myamp.f)
F90-S-0038-Symbol, s_qpdf, has not been explicitly declared (myamp.f)
  0 inform,   0 warnings,  18 severes, 0 fatal for cut_bw
F90-S-0023-Syntax error - unbalanced parentheses (../../Source/genps.inc: 9)
F90-S-0087-Non-constant expression where constant expression required (../../Source/genps.inc: 25)
F90-S-0087-Non-constant expression where constant expression required (../../Source/genps.inc: 27)
F90-S-0034-Syntax error at or near end of line (../../Source/run.inc: 10)
F90-S-0023-Syntax error - unbalanced parentheses (../../Source/run.inc: 55)
F90-S-0023-Syntax error - unbalanced parentheses (../../Source/run.inc: 56)
F90-S-0023-Syntax error - unbalanced parentheses (myamp.f: 273)
F90-S-0023-Syntax error - unbalanced parentheses (myamp.f: 275)
F90-S-0050-Assumed size array, spole, is not a dummy argument (myamp.f: 283)
F90-S-0050-Assumed size array, swidth, is not a dummy argument (myamp.f: 283)
F90-S-0023-Syntax error - unbalanced parentheses (myamp.f: 298)
F90-S-0023-Syntax error - unbalanced parentheses (myamp.f: 323)
F90-S-0034-Syntax error at or near end of line (myamp.f: 370)
F90-S-0023-Syntax error - unbalanced parentheses (myamp.f: 396)
F90-S-0023-Syntax error - unbalanced parentheses (myamp.f: 399)
F90-S-0023-Syntax error - unbalanced parentheses (myamp.f: 410)
F90-S-0034-Syntax error at or near end of line (myamp.f: 422)
F90-S-0034-Syntax error at or near . (myamp.f: 429)
F90-S-0023-Syntax error - unbalanced parentheses (myamp.f: 436)