Add option to set maximum GRF number that vISA can select

New vISA option ``-maxGRFNum`` restrics the maximum GRF number to be
selected by vISA.

Author: jfuentes

visa/G4_Kernel.cpp

@@ -2082,21 +2082,30 @@ GRFMode::GRFMode(const TARGET_PLATFORM platform, Options *op) : options(op) {
     defaultMode = 0;
   }
   currentMode = defaultMode;
+
+  // Set upper bound GRF
+  unsigned maxGRF = op->getuInt32Option(vISA_MaxGRFNum);
+  upperBoundGRF = maxGRF > 0 ? maxGRF : configs.back().numGRF;
+  vISA_ASSERT(isValidNumGRFs(upperBoundGRF), "Invalid upper bound for GRF number");
 }
 
-unsigned GRFMode::setModeByRegPressure(unsigned maxRP, unsigned largestInputReg) {
+unsigned GRFMode::setModeByRegPressure(unsigned maxRP,
+                                       unsigned largestInputReg) {
   unsigned size = configs.size(), i = 0;
   // find appropiate GRF based on reg pressure
   for (; i < size; i++) {
-    if (configs[i].VRTEnable && maxRP <= configs[i].numGRF &&
-        // Check that we've at least 8 GRFs over and above
-        // those blocked for kernel input. This helps cases
-        // where an 8 GRF variable shows up in entry BB.
-        (largestInputReg + 8) <= configs[i].numGRF) {
+    if (configs[i].VRTEnable && configs[i].numGRF <= upperBoundGRF) {
       currentMode = i;
-      break;
+      if (maxRP <= configs[i].numGRF &&
+          // Check that we've at least 8 GRFs over and above
+          // those blocked for kernel input. This helps cases
+          // where an 8 GRF variable shows up in entry BB.
+          (largestInputReg + 8) <= configs[i].numGRF)
+        return configs[currentMode].numGRF;
     }
   }
+  // RP is greater than the maximum GRF available, so set the largest GRF
+  // available
   return configs[currentMode].numGRF;
 }
 

visa/G4_Kernel.hpp

@@ -178,16 +178,18 @@ class GRFMode {
   }
 
   unsigned getMaxGRF() const {
-    auto found = std::find_if(configs.rbegin(), configs.rend(),
-                              [](const Config &c) { return c.VRTEnable; });
+    auto found =
+        std::find_if(configs.rbegin(), configs.rend(), [this](const Config &c) {
+          return c.VRTEnable && c.numGRF <= upperBoundGRF;
+        });
     return found->numGRF;
   }
 
   // Get the next larger GRF available
   unsigned getLargerGRF() const {
     // find the first larger mode that's available for VRT
     for (auto i = currentMode + 1; i < configs.size(); ++i) {
-      if (configs[i].VRTEnable)
+      if (configs[i].VRTEnable && configs[i].numGRF <= upperBoundGRF)
         return configs[i].numGRF;
     }
     return configs[currentMode].numGRF;
@@ -205,7 +207,7 @@ class GRFMode {
   // Move GRF mode to the larger GRF available and return the number
   unsigned moveToLargerGRF() {
     for (auto i = currentMode + 1; i < configs.size(); ++i) {
-      if (configs[i].VRTEnable) {
+      if (configs[i].VRTEnable && configs[i].numGRF <= upperBoundGRF) {
         currentMode = i;
         break;
       }
@@ -248,6 +250,7 @@ class GRFMode {
   std::vector<Config> configs;
   unsigned defaultMode;
   unsigned currentMode;
+  unsigned upperBoundGRF;
   Options *options;
 };
 

visa/include/VISAOptionsDefs.h

@@ -281,6 +281,9 @@ DEF_VISA_OPTION(vISA_ReservedGRFNum, ET_INT32, "-reservedGRFNum",
                 "USAGE: -reservedGRFNum <regNum>\n", 0)
 DEF_VISA_OPTION(vISA_TotalGRFNum, ET_INT32, "-TotalGRFNum",
                 "USAGE: -TotalGRFNum <regNum>\n", 128)
+DEF_VISA_OPTION(vISA_MaxGRFNum, ET_INT32, "-maxGRFNum",
+                "Set the upper bound GRF for auto GRF selection."
+                "USAGE: -maxGRFNum <regNum>. 0 means no maximum number.\n", 0)
 DEF_VISA_OPTION(vISA_RATrace, ET_BOOL, "-ratrace", UNUSED, false)
 DEF_VISA_OPTION(vISA_FastSpill, ET_BOOL, "-fasterRA", UNUSED, false)
 DEF_VISA_OPTION(vISA_AbortOnSpillThreshold, ET_INT32, "-abortOnSpill", UNUSED,