Enhanced max slew fixing to resolve large unfixed violations

1) Added extra step to fix slew violations at load pins
2) Used actual slews from STA if possible, not just lumped RC estimates
3) Fixed a bug that led to overfixing due to wrong driver selection after buffering

Signed-off-by: Cho Moon <cmoon@precisioninno.com>

Author: precisionmoon

src/rsz/src/BufferedNet.cc

@@ -80,6 +80,7 @@ BufferedNet::BufferedNet(const BufferedNetType type,
   type_ = BufferedNetType::load;
   location_ = location;
   load_pin_ = load_pin;
+  corner_ = corner;
 
   LibertyPort* load_port = resizer->network()->libertyPort(load_pin);
   if (load_port) {
@@ -105,6 +106,7 @@ BufferedNet::BufferedNet(const BufferedNetType type,
   layer_ = null_layer;
   ref_ = ref;
   ref2_ = ref2;
+  corner_ = ref->corner();
 
   cap_ = ref->cap() + ref2->cap();
   fanout_ = ref->fanout() + ref2->fanout();
@@ -130,6 +132,7 @@ BufferedNet::BufferedNet(const BufferedNetType type,
   location_ = location;
   layer_ = layer;
   ref_ = ref;
+  corner_ = corner;
 
   double wire_res, wire_cap;
   wireRC(corner, resizer, estimate_parasitics, wire_res, wire_cap);
@@ -158,6 +161,7 @@ BufferedNet::BufferedNet(const BufferedNetType type,
   buffer_cell_ = buffer_cell;
   layer_ = null_layer;
   ref_ = ref;
+  corner_ = corner;
 
   LibertyPort *input, *output;
   buffer_cell->bufferPorts(input, output);

src/rsz/src/BufferedNet.hh

@@ -247,6 +247,7 @@ class BufferedNet
   }
 
   bool fitsEnvelope(Metrics target);
+  const Corner* corner() { return corner_; }
 
  private:
   BufferedNetType type_;
@@ -283,6 +284,8 @@ class BufferedNet
 
   // Delay from driver pin to here
   FixedDelay arrival_delay_ = FixedDelay::ZERO;
+
+  const Corner* corner_ = nullptr;
 };
 
 }  // namespace rsz