Generate compile_commands.json for an MPI project

Run the build under Bear exactly as you would without MPI:

bear -- make

A build that compiles through mpicc, mpicxx, mpifort, or one of the Intel MPI wrappers needs no special configuration: Bear recognizes all of them and records the wrapper invocation itself. See MPI compiler wrappers and Supported compilers for the full name table and the wrapper-is-recorded-as-invoked contract in general. This page covers what that contract means in practice: what actually lands in the recorded entry, and the one place the database can differ from what a reader expects.

Open MPI/MPICH vs. Intel

Open MPI’s and MPICH’s wrappers share one family id, mpi, and parse with the GCC flag table. Intel’s wrappers (mpiicc, mpiifort, and the rest) are recognized too, but as extra names on the intel_cc and intel_fortran families instead of the generic mpi id: mpiicc is icc/icx with MPI’s paths baked in, and Intel’s flag table has arity rules (for example -debug takes a following argument) that the GCC table would mis-parse. See Use Bear with Intel oneAPI compilers for those two families in general.

What actually lands in the entry

Given

mpicc -c main.c -o main.o

where mpicc is a script that execs gcc with -I/opt/mpi/include -L/opt/mpi/lib prepended, the entry Bear writes is

[
  {
    "file": "main.c",
    "arguments": ["mpicc", "-c", "main.c", "-o", "main.o"],
    "directory": "/path/to/project",
    "output": "main.o"
  }
]

arguments holds the command exactly as the build wrote it: no gcc, and none of the wrapper’s baked-in -I/-L flags, since Bear does not run the wrapper to learn them. Clang tooling that needs those flags to resolve MPI headers should point at the wrapper directly; clangd does this with --query-driver. See Set up clangd for a project without CMake for pointing an editor at the database this page produces.

The compiler the wrapper execs is usually not a second entry

In preload mode Bear does intercept the compiler the wrapper execs internally, not just the wrapper itself, but that rarely shows up as a second entry in compile_commands.json: the default duplicate filter (directory and file) treats the two invocations as the same compilation and keeps whichever comes first, the wrapper’s. That lower-level invocation surfaces as its own entry only if you widen duplicates.match_on to include arguments (see Configure Bear); ordinarily that is not useful, since it names an intermediate compiler call rather than the one your build system actually asked for.

MPICH’s compiler-override options, -cc=, -cxx=, and -fc=, are also accepted without the = (-cc gcc); either form is recognized as a driver option that takes a value, so it never gets misread as compiling a source file named gcc.

Related pages

• Use Bear with Intel oneAPI compilers for the intel_cc/intel_fortran families the Intel MPI wrappers reuse.
• Use Bear with ccache, distcc, or icecc for the launcher case this page contrasts with.
• Supported compilers for the full recognized-name table.
• Recipes for the rest of the task pages.