[Flang] validation failure in 416.gamess@ref

[vzakhari]

Specdiff is reporting the following miscompare:

0397:       EXTRAP=T  DAMP=T  SHIFT=T  RSTRCT=F  DIIS=F  SOSCF=T
            EXTRAP=T  DAMP=F  SHIFT=F  RSTRCT=F  DIIS=F  SOSCF=T
                          ^

Values computed for DAMP is not passed correctly to Fortran runtime:

 4019       SUBROUTINE UHFOP(SZ,S2)
...
 4187       DAMPH  = MOD(MCONV,4)  .GE. 2
 4188       VSHIFT = MOD(MCONV,8)  .GE. 4
...
 4591          IF(SOME) WRITE(IW,9020) EN,MAXIT,MPUNCH,MUL,EXTRAH,DAMPH,
 4592      *                  VSHIFT,RSTRCT,DODIIS,SOSCF

The problem appears after SLPVectorizerPass with -march=native (Icelake), but it is just a trigger.

I believe the following C++ test demonstrates the problem:

1. repro.cpp mimics the Fortran code:

extern void printer(bool x);

__attribute__((noinline)) void test(int x) {
  bool t1 = (x % 4) >= 2;
  bool t2 = (x % 8) >= 4;
  printer(t1);
  printer(t2);
}

int main() {
  test(65);
}

2. report_rt.cpp mimics Fortran runtime code that prints logical values:

#include <cstdint>
#include <cstdio>
__attribute__((noinline)) void printer2(void *x) {
  printf("%s\n", *(std::int8_t *)x ? "T" : "F");
}

__attribute__((noinline)) void printer(bool x) {
  printer2(reinterpret_cast<void *>(&x));
}

Compilation commands to reproduce the issue:

$ clang++ repro.cpp -march=native -O3 -emit-llvm -Xclang -disable-llvm-passes -S -o repro_orig.ll
$ clang++ -march=native -O3 repro_rt.cpp repro_orig.ll
$ ./a.out
F
F

This is the correct result above, but it becomes incorrect (as with Flang generated code) when I remove zeroext attribute from _Z7printerb in repro_orig.ll - see attached repro_error.ll:

$ clang++ -march=native -O3 repro_rt.cpp repro_error.ll
$ ./a.out
T
T

So the problem is that the caller of printer does not zero extends the i1 argument before the calls as required by ABI because of the missing zeroext attribute.

repro_orig.ll.gz
repro_error.ll.gz

[llvmbot]

@llvm/issue-subscribers-flang-ir