vpr: If logic block type can't be identified default to 100% pin util targets

Previously would halt with an assertion error. We now produce warning
messages instead (warning that this may produce a denser packing than
desired) and allow the tool to continue using the relaxed targets.

Closes #556

Author: kmurray

vpr/src/pack/pack.cpp

@@ -320,12 +320,16 @@ static t_ext_pin_util_targets parse_target_external_pin_util(std::vector<std::st
         //For relatively high pin utilizations (e.g. > 70%) this has little-to-no
         //impact on the number of clusters required. As a result we set a default 
         //input pin utilization target which is high, but less than 100%.
-        constexpr float LOGIC_BLOCK_TYPE_AUTO_INPUT_UTIL = 0.8;
-        constexpr float LOGIC_BLOCK_TYPE_AUTO_OUTPUT_UTIL = 1.0;
+        if (logic_block_type != nullptr) {
+            constexpr float LOGIC_BLOCK_TYPE_AUTO_INPUT_UTIL = 0.8;
+            constexpr float LOGIC_BLOCK_TYPE_AUTO_OUTPUT_UTIL = 1.0;
 
-        t_ext_pin_util logic_block_ext_pin_util(LOGIC_BLOCK_TYPE_AUTO_INPUT_UTIL , LOGIC_BLOCK_TYPE_AUTO_OUTPUT_UTIL);
+            t_ext_pin_util logic_block_ext_pin_util(LOGIC_BLOCK_TYPE_AUTO_INPUT_UTIL , LOGIC_BLOCK_TYPE_AUTO_OUTPUT_UTIL);
 
-        targets.set_block_pin_util(logic_block_type->name, logic_block_ext_pin_util);
+            targets.set_block_pin_util(logic_block_type->name, logic_block_ext_pin_util);
+        } else {
+            VTR_LOG_WARN("Unable to identify logic block type to apply default pin utilization targets to; this may result in denser packing than desired\n");
+        }
 
     } else {
         //Process user specified overrides

vpr/src/util/vpr_utils.cpp

@@ -752,7 +752,11 @@ t_type_ptr infer_logic_block_type(const DeviceGrid& grid) {
         return logic_block_candidates.front();
     } else {
         //Otherwise assume it is the most common block type
-        return find_most_common_block_type(grid);
+        auto most_common_type = find_most_common_block_type(grid);
+        if (most_common_type == nullptr) {
+            VTR_LOG_WARN("Unable to infer which block type is a logic block\n");
+        }
+        return most_common_type;
     }
 }
 
@@ -771,7 +775,9 @@ t_type_ptr find_most_common_block_type(const DeviceGrid& grid) {
         }
     }
 
-    VTR_ASSERT(max_type);
+    if (max_type == nullptr) {
+        VTR_LOG_WARN("Unable to determine most common block type (perhaps the device grid was empty?)\n");    
+    }
     return max_type;
 }