Fix the fmax calculation for mulitple combinational paths

Signed-off-by: Matt Liberty <mliberty@precisioninno.com>

Author: maliberty

src/Metrics.tcl

@@ -87,17 +87,25 @@ proc report_fmax_metric { args } {
   if { $fmax_metric == 0 } {
     # attempt to compute based on combinatorial path
     set fmax_valid true
-    set max_path [find_timing_paths -unconstrained -path_delay max]
-    if { $max_path == "" } {
+    set max_paths [find_timing_paths -unconstrained -path_delay max]
+    if { $max_paths == "" } {
       set fmax_valid false
     } else {
-      set max_path_delay [$max_path data_arrival_time]
+      set max_path_delay -1
+      foreach path $max_paths {
+        set path_delay [$path data_arrival_time]
+        set max_path_delay [expr { max($max_path_delay, $path_delay) }]
+      }
     }
-    set min_path [find_timing_paths -unconstrained -path_delay min]
-    if { $min_path == "" } {
+    set min_paths [find_timing_paths -unconstrained -path_delay min]
+    if { $min_paths == "" } {
       set fmax_valid false
     } else {
-      set min_path_delay [$min_path data_arrival_time]
+      set min_path_delay 1e12
+      foreach path $min_paths {
+        set path_delay [$path data_arrival_time]
+        set min_path_delay [expr { min($min_path_delay, $path_delay) }]
+      }
     }
     if { $fmax_valid } {
       set path_delay [expr { $max_path_delay - min(0, $min_path_delay) }]