[GLOP] remove unused flag; do not recompute prices if we are not going to use them

ortools/glop/lp_solver.cc

@@ -35,10 +35,6 @@
 #include "ortools/util/file_util.h"
 #endif
 
-ABSL_FLAG(bool, lp_solver_enable_fp_exceptions, false,
-          "When true, NaNs and division / zero produce errors. "
-          "This is very useful for debugging, but incompatible with LLVM. "
-          "It is recommended to set this to false for production usage.");
 ABSL_FLAG(bool, lp_dump_to_proto_file, false,
           "Tells whether do dump the problem to a protobuf file.");
 ABSL_FLAG(bool, lp_dump_compressed_file, true,
@@ -172,18 +168,6 @@ ProblemStatus LPSolver::SolveWithTimeLimit(const LinearProgram& lp,
          "\n* compiling with optimizations enabled and by defining NDEBUG.   *"
          "\n******************************************************************";
 
-  // Note that we only activate the floating-point exceptions after we are sure
-  // that the program is valid. This way, if we have input NaNs, we will not
-  // crash.
-  ScopedFloatingPointEnv scoped_fenv;
-  if (absl::GetFlag(FLAGS_lp_solver_enable_fp_exceptions)) {
-#ifdef _MSC_VER
-    scoped_fenv.EnableExceptions(_EM_INVALID | EM_ZERODIVIDE);
-#else
-    scoped_fenv.EnableExceptions(FE_DIVBYZERO | FE_INVALID);
-#endif
-  }
-
   // Setup the logger.
   logger_.EnableLogging(parameters_.log_search_progress());
   logger_.SetLogToStdOut(parameters_.log_to_stdout());

ortools/glop/revised_simplex.cc

@@ -2165,6 +2165,19 @@ void RevisedSimplex::OnDualPriceChange(const DenseColumn& squared_norm,
 void RevisedSimplex::DualPhaseIUpdatePrice(RowIndex leaving_row,
                                            ColIndex entering_col) {
   SCOPED_TIME_STAT(&function_stats_);
+
+  // If the prices are going to be recomputed, there is nothing to do. See the
+  // logic at the beginning of DualPhaseIChooseLeavingVariableRow() which must
+  // be in sync with this one.
+  //
+  // TODO(user): Move the logic in a single class, so it is easier to enforce
+  // invariant.
+  if (reduced_costs_.AreReducedCostsRecomputed() ||
+      dual_edge_norms_.NeedsBasisRefactorization() ||
+      dual_pricing_vector_.empty()) {
+    return;
+  }
+
   const VariableTypeRow& variable_type = variables_info_.GetTypeRow();
   const Fractional threshold = parameters_.ratio_test_zero_threshold();