"[Autobackout][FunctionalRegression]Revert of change: 8326cad: Allow unconstrained ranges to use RR policy even when other

    variables use FF

Unconstrained variables at bottom of coloring stack cannot spill and are
    guaranteed to get an allocation. So even when rest of the variables use
    first fit, we make unconstrained variables use round robin as that can
    ease reuse, giving more leeway to postRA scheduler and postRA spill
    cleanup.

    Note that we do this only for non sub-reg allocations only. Because
    sub-reg allocations are packed together so they don't necessarily even
    honor first fit."

Author: sys-igc

visa/GraphColor.cpp

@@ -7061,8 +7061,6 @@ void GraphColor::determineColorOrdering() {
   //This will not change the order unless SPGSS is turned on
   builder.getFreqInfoManager().sortBasedOnFreq(sorted);
 
-  bool isStackCall = kernel.fg.getIsStackCallFunc();
-
   for (unsigned i = 0; i < numUnassignedVar; i++) {
     LiveRange *lr = sorted[i];
     unsigned availColor = numColor;
@@ -7071,12 +7069,9 @@ void GraphColor::determineColorOrdering() {
     if (lr->getDegree() + lr->getNumRegNeeded() <= availColor) {
       unconstrainedWorklist.push_back(lr);
       lr->setActive(false);
-      if (!isStackCall &&
-          (lr->getRegKind() & G4_GRF)) {
+      if (lr->getRegKind() == G4_GRF) {
         // Mark current lr as unconstrained, which means RR algorithm can always
-        // be applied to the variable. We should not apply this for stackcall
-        // functions because if we do RR, we may end up using GRFs from callee
-        // saved partition, requiring save/restore.
+        // be applied to the variable.
         lr->setUnconstrained(true);
       }
     } else {
@@ -7330,7 +7325,12 @@ bool GraphColor::assignColors(ColorHeuristic colorHeuristicGRF,
       }
 
       if (kernel.getOption(vISA_GCRRInFF)) {
-        if (heuristic == FIRST_FIT && !lr->getIsUnconstrained()) {
+        if (lr->getRegKind() != G4_GRF) {
+          // None GRF assignment, keep single FF or RR algorithm
+          if (heuristic == FIRST_FIT) {
+            parms.setStartGRF(0);
+          }
+        } else if (heuristic == FIRST_FIT && !lr->getIsUnconstrained()) {
           // GRF assignment, start GRF is always 0 if first fit algorithm is
           // used and the variable is constrainted
           parms.setStartGRF(0);

visa/PhyRegUsage.cpp

@@ -726,6 +726,9 @@ PhyRegUsage::findGRFSubReg(const BitSet *forbidden, bool calleeSaveBias,
                            G4_SubReg_Align subAlign, unsigned nwords) {
   int startReg = 0, endReg = totalGRFNum;
   PhyReg phyReg = {-1, -1};
+  if (builder.getOption(vISA_GCRRInFF)) {
+    startReg = AS.startGRFReg;
+  }
 
   if (calleeSaveBias) {
     startReg = builder.kernel.stackCall.calleeSaveStart();
@@ -775,7 +778,17 @@ PhyRegUsage::findGRFSubReg(const BitSet *forbidden, bool calleeSaveBias,
   }
 
   // Find sub-GRF allocation throughout GRF file
-  phyReg = findSubGRFAlloc(0, totalGRFNum);
+  if (builder.getOption(vISA_GCRRInFF)) {
+    phyReg = findSubGRFAlloc(startReg, totalGRFNum);
+    if (phyReg.subreg == -1) {
+      phyReg = findSubGRFAlloc(0, AS.startGRFReg);
+    }
+    if (phyReg.subreg != -1) {
+      AS.startGRFReg = (phyReg.reg + 1) % totalGRFNum;
+    }
+  } else {
+    phyReg = findSubGRFAlloc(0, totalGRFNum);
+  }
 
   return phyReg;
 }
@@ -958,14 +971,11 @@ bool PhyRegUsage::assignRegs(bool highInternalConflict, LiveRange *varBasis,
 
       bool forceCalleeSaveAlloc = builder.kernel.fg.isPseudoVCEDcl(decl);
       unsigned short occupiedBundles = getOccupiedBundle(decl);
-      int GRFForFF = AS.startGRFReg;
       bool success = findContiguousGRF(
           FPR.availableGregs, forbidden, occupiedBundles,
           getAlignToUse(align, bankAlign), decl->getNumRows(), endGRFReg,
           AS.startGRFReg, i, forceCalleeSaveAlloc, varBasis->getEOTSrc());
       if (!success && occupiedBundles) {
-        if (colorHeuristic == FIRST_FIT && !varBasis->getIsUnconstrained())
-          AS.startGRFReg = GRFForFF;
         success = findContiguousGRF(
             FPR.availableGregs, forbidden, 0,
             getAlignToUse(align, bankAlign), decl->getNumRows(), endGRFReg,

visa/include/VISAOptionsDefs.h

@@ -487,7 +487,7 @@ DEF_VISA_OPTION(vISA_FailSafeRALimit, ET_INT32, "-failSafeRALimit", UNUSED, 3)
 DEF_VISA_OPTION(vISA_DenseMatrixLimit, ET_INT32, "-denseMatrixLimit", UNUSED,
                 0x800)
 DEF_VISA_OPTION(vISA_FillConstOpt, ET_BOOL, "-nofillconstopt", UNUSED, true)
-DEF_VISA_OPTION(vISA_GCRRInFF, ET_BOOL_TRUE, "-GCRRinFF", UNUSED, true)
+DEF_VISA_OPTION(vISA_GCRRInFF, ET_BOOL, "-GCRRinFF", UNUSED, false)
 DEF_VISA_OPTION(vISA_IncrementalRA, ET_INT32, "-incrementalra",
                 "USAGE: -incrementalra <0|1|2> where 0 is disabled, 1 is enabled, 2 is enabled with verification", 0)
 DEF_VISA_OPTION(vISA_SplitAlignedScalarMinDist, ET_INT32,