Avoid O(n^2) iteration over kernel declares.

Author: pratikashar

visa/GraphColor.cpp

@@ -1782,6 +1782,45 @@ void Interference::addCalleeSaveBias(const BitSet& live)
     }
 }
 
+void Interference::buildInterferenceAmongLiveOuts()
+{
+    // Mark interference between dcls marked as Output.
+    //
+    // Interference computation marks interference for a
+    // variable only when definition for that variable is
+    // seen, not otherwise.
+    //
+    // This method is useful when definition of such
+    // "Output" variables are emitted to program post RA.
+    //
+    // It is safe to mark interference between all "Output"
+    // dcls even when their definition is present in the program.
+
+    // First gather all Output dcls in a vector to avoid an O(N^2)
+    // lookup. Number of OutputDcls should be small.
+    std::vector<G4_Declare*> OutputDcls;
+    for (auto dcl : kernel.Declares)
+    {
+        if (!dcl->getRegVar()->isRegAllocPartaker() ||
+            !dcl->isOutput())
+            continue;
+
+        OutputDcls.push_back(dcl);
+    }
+
+    for (auto dcl1 : OutputDcls)
+    {
+        // dcl1 is RA partaker iter and is marked as Output
+        for (auto dcl2 : OutputDcls)
+        {
+            if (dcl1 == dcl2)
+                continue;
+
+            checkAndSetIntf(dcl1->getRegVar()->getId(), dcl2->getRegVar()->getId());
+        }
+    }
+}
+
 void Interference::buildInterferenceAmongLiveIns()
 {
     //
@@ -2448,6 +2487,8 @@ void Interference::computeInterference()
     //
     BitSet live(maxId, false);
 
+    buildInterferenceAmongLiveOuts();
+
     for (G4_BB *bb : kernel.fg)
     {
         //

visa/GraphColor.h

@@ -446,6 +446,7 @@ namespace vISA
 
         void buildInterferenceWithLocalRA(G4_BB* bb);
 
+        void buildInterferenceAmongLiveOuts();
         void buildInterferenceAmongLiveIns();
 
         void markInterferenceToAvoidDstSrcOverlap(G4_BB* bb, G4_INST* inst);

visa/SpillManagerGMRF.cpp

@@ -4710,6 +4710,7 @@ void GlobalRA::expandFillStackcall(uint32_t numRows, uint32_t offset, short rowO
     }
 }
 
+
 void GlobalRA::expandFillIntrinsic(G4_BB* bb)
 {
     // fill (1) fill_var:ud     bitmask:ud     offset:ud