detect missing initialization and run it instead of crashing with a non-descript segfault

src/compute_reduce.cpp

@@ -30,8 +30,8 @@
 
 using namespace LAMMPS_NS;
 
-enum{SUM,SUMSQ,MINN,MAXX,AVE,AVESQ};             // also in ReduceRegion
+enum{SUM,SUMSQ,MINN,MAXX,AVE,AVESQ};             // also in ComputeReduceRegion
-enum{X,V,F,COMPUTE,FIX,VARIABLE};
+enum{UNKNOWN=-1,X,V,F,COMPUTE,FIX,VARIABLE};
 enum{PERATOM,LOCAL};
 
 #define INVOKED_VECTOR 2
@@ -92,6 +92,10 @@ ComputeReduce::ComputeReduce(LAMMPS *lmp, int narg, char **arg) :
   flavor = new int[nargnew];
   ids = new char*[nargnew];
   value2index = new int[nargnew];
+  for (int i=0; i < nargnew; ++i) {
+    which[i] = argindex[i] = flavor[i] = value2index[i] = UNKNOWN;
+    ids[i] = NULL;
+  }
   nvalues = 0;
 
   iarg = 0;
@@ -345,7 +349,7 @@ void ComputeReduce::init()
         error->all(FLERR,"Variable name for compute reduce does not exist");
       value2index[m] = ivariable;
 
-    } else value2index[m] = -1;
+    } else value2index[m] = UNKNOWN;
   }
 
   // set index and check validity of region
@@ -468,8 +472,16 @@ double ComputeReduce::compute_one(int m, int flag)
 
   index = -1;
   int vidx = value2index[m];
-  int aidx = argindex[m];
 
+  // initialization in case it has not yet been run, e.g. when
+  // the compute was invoked right after it has been created
+
+  if (vidx == UNKNOWN) {
+    init();
+    vidx = value2index[m];
+  }
+
+  int aidx = argindex[m];
   int *mask = atom->mask;
   int nlocal = atom->nlocal;
 

src/compute_reduce_chunk.cpp

@@ -28,7 +28,7 @@
 using namespace LAMMPS_NS;
 
 enum{SUM,MINN,MAXX};
-enum{COMPUTE,FIX,VARIABLE};
+enum{UNKNOWN=-1,COMPUTE,FIX,VARIABLE};
 
 #define INVOKED_PERATOM 8
 
@@ -74,6 +74,10 @@ ComputeReduceChunk::ComputeReduceChunk(LAMMPS *lmp, int narg, char **arg) :
   argindex = new int[nargnew];
   ids = new char*[nargnew];
   value2index = new int[nargnew];
+  for (int i=0; i < nargnew; ++i) {
+    which[i] = argindex[i] = value2index[i] = UNKNOWN;
+    ids[i] = NULL;
+  }
   nvalues = 0;
 
   iarg = 0;
@@ -354,10 +358,19 @@ void ComputeReduceChunk::compute_one(int m, double *vchunk, int nstride)
   int *mask = atom->mask;
   int nlocal = atom->nlocal;
 
-  int index;
+  int index = -1;
+  int vidx = value2index[m];
+
+  // initialization in case it has not yet been run, e.g. when
+  // the compute was invoked right after it has been created
+
+  if (vidx == UNKNOWN) {
+    init();
+    vidx = value2index[m];
+  }
 
   if (which[m] == COMPUTE) {
-    Compute *compute = modify->compute[value2index[m]];
+    Compute *compute = modify->compute[vidx];
 
     if (!(compute->invoked_flag & INVOKED_PERATOM)) {
       compute->compute_peratom();
@@ -386,7 +399,7 @@ void ComputeReduceChunk::compute_one(int m, double *vchunk, int nstride)
   // access fix fields, check if fix frequency is a match
 
   } else if (which[m] == FIX) {
-    Fix *fix = modify->fix[value2index[m]];
+    Fix *fix = modify->fix[vidx];
     if (update->ntimestep % fix->peratom_freq)
       error->all(FLERR,"Fix used in compute reduce/chunk not "
                  "computed at compatible time");
@@ -419,7 +432,7 @@ void ComputeReduceChunk::compute_one(int m, double *vchunk, int nstride)
       memory->create(varatom,maxatom,"reduce/chunk:varatom");
     }
 
-    input->variable->compute_atom(value2index[m],igroup,varatom,1,0);
+    input->variable->compute_atom(vidx,igroup,varatom,1,0);
     for (int i = 0; i < nlocal; i++) {
       if (!(mask[i] & groupbit)) continue;
       index = ichunk[i]-1;

src/compute_reduce_region.cpp

@@ -29,7 +29,7 @@
 using namespace LAMMPS_NS;
 
 enum{SUM,SUMSQ,MINN,MAXX,AVE,AVESQ};             // also in ComputeReduce
-enum{X,V,F,COMPUTE,FIX,VARIABLE};
+enum{UNKNOWN=-1,X,V,F,COMPUTE,FIX,VARIABLE};
 enum{PERATOM,LOCAL};
 
 #define INVOKED_VECTOR 2
@@ -70,6 +70,15 @@ double ComputeReduceRegion::compute_one(int m, int flag)
   int nlocal = atom->nlocal;
 
   int n = value2index[m];
+
+  // initialization in case it has not yet been run,
+  // e.g. when invoked
+  if (n == UNKNOWN) {
+    init();
+    n = value2index[m];
+  }
+
+  int aidx = argindex[m];
   int j = argindex[m];
 
   double one = 0.0;