[ClusterLegalizer] Fixed Memory Leak

A memory leak was able to occur if the external pin utilization string was
set to an invalid number. This was caught by the CI, which inexplicably
came back to life today.

vpr/src/pack/cluster_legalizer.cpp

@@ -1637,6 +1637,19 @@ ClusterLegalizer::ClusterLegalizer(const AtomNetlist& atom_netlist,
     // Verify that the inputs are valid.
     VTR_ASSERT_SAFE(lb_type_rr_graphs != nullptr);
 
+    // Get the target external pin utilization
+    // NOTE: This has to be initialized first due to the fact that VPR_FATA_ERROR
+    //       may be called within the constructor of t_ext_pin_util_targets. If
+    //       this occurs, the destructor may or may not be called (honestly I have
+    //       no idea why it does or does not, but it changes based on how VPR
+    //       is compiled...). If the destructor is not called, it is important
+    //       that nothing was allocated before this line is called. If the
+    //       destructor is called, we just need to be careful of double freeing
+    //       (check if the allocated member variables are nullptr).
+    // FIXME: This can be fixed by removing all allocations from the constructor
+    //        (see cluster_placement_stats_).
+    target_external_pin_util_ = t_ext_pin_util_targets(target_external_pin_util_str);
+
     // Resize the atom_cluster lookup to make the accesses much cheaper.
     atom_cluster_.resize(atom_netlist.blocks().size(), LegalizationClusterId::INVALID());
     // Allocate the cluster_placement_stats
@@ -1662,15 +1675,6 @@ ClusterLegalizer::ClusterLegalizer(const AtomNetlist& atom_netlist,
     enable_pin_feasibility_filter_ = enable_pin_feasibility_filter;
     feasible_block_array_size_ = feasible_block_array_size;
     log_verbosity_ = log_verbosity;
-    // Get the target external pin utilization
-    // NOTE: This has to be initialized last due to the fact that VPR_FATA_ERROR
-    //       may be called within the constructor of t_ext_pin_util_targets. If
-    //       this occurs, an excpetion is thrown which will drain the stack. If
-    //       the cluster legalizer object is stored on the stack, this can call
-    //       the destructor prematurely (before certain structures are allocated).
-    //       Therefore, this is created at the end, when the class is in a state
-    //       where it can be destroyed.
-    target_external_pin_util_ = t_ext_pin_util_targets(target_external_pin_util_str);
 }
 
 void ClusterLegalizer::reset() {
@@ -1776,6 +1780,7 @@ ClusterLegalizer::~ClusterLegalizer() {
         destroy_cluster(cluster_id);
     }
     // Free the cluster_placement_stats
-    free_cluster_placement_stats(cluster_placement_stats_);
+    if (cluster_placement_stats_ != nullptr)
+        free_cluster_placement_stats(cluster_placement_stats_);
 }