This optimization greatly enhances efficiency of creating new instructions by

masking and shifting operands directly into their place in the instruction,
instead of the old-fashioned way of ORing in each bit separately.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@7179 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 106 insertions, 6 deletions

diff --git a/utils/TableGen/CodeEmitterGen.cpp b/utils/TableGen/CodeEmitterGen.cpp
index 9d0d939c9d..8cb7979333 100644
--- a/utils/TableGen/CodeEmitterGen.cpp
+++ b/utils/TableGen/CodeEmitterGen.cpp
@@ -59,6 +59,7 @@ void CodeEmitterGen::createEmitter(std::ostream &o) {
     //
     unsigned op = 0;
     std::map<const std::string,unsigned> OpOrder;
+    std::map<const std::string,bool> OpContinuous;
     for (unsigned i = 0, e = Vals.size(); i != e; ++i) {
       if (Vals[i].getName() != "Inst" && 
           !Vals[i].getValue()->isComplete() &&
@@ -71,6 +72,90 @@ void CodeEmitterGen::createEmitter(std::ostream &o) {
           <<" = getMachineOpValue(MI, MI.getOperand("<<op<<"));\n";
         //<< "      MachineOperand &op" << op <<" = MI.getOperand("<<op<<");\n";
         OpOrder[Vals[i].getName()] = op++;
+
+        // Is the operand continuous? If so, we can just mask and OR it in
+        // instead of doing it bit-by-bit, saving a lot in runtime cost.        
+        const BitsInit *InstInit = BI;
+        int beginBitInVar = -1, endBitInVar = -1,
+          beginBitInInst = -1, endBitInInst = -1;
+        bool continuous = true;
+
+        for (int bit = InstInit->getNumBits()-1; bit >= 0; --bit) {
+          if (VarBitInit *VBI =
+              dynamic_cast<VarBitInit*>(InstInit->getBit(bit))) {
+            TypedInit *TI = VBI->getVariable();
+            if (VarInit *VI = dynamic_cast<VarInit*>(TI)) {
+              // only process the current variable
+              if (VI->getName() != Vals[i].getName())
+                continue;
+
+              if (beginBitInVar == -1)
+                beginBitInVar = VBI->getBitNum();
+
+              if (endBitInVar == -1)
+                endBitInVar = VBI->getBitNum();
+              else {
+                if (endBitInVar == (int)VBI->getBitNum() + 1)
+                  endBitInVar = VBI->getBitNum();
+                else {
+                  continuous = false;
+                  break;
+                }
+              }
+
+              if (beginBitInInst == -1)
+                beginBitInInst = bit;
+              if (endBitInInst == -1)
+                endBitInInst = bit;
+              else {
+                if (endBitInInst == bit + 1)
+                  endBitInInst = bit;
+                else {
+                  continuous = false;
+                  break;
+                }
+              }
+
+              // maintain same distance between bits in field and bits in
+              // instruction. if the relative distances stay the same
+              // throughout,
+              if ((beginBitInVar - (int)VBI->getBitNum()) !=
+                  (beginBitInInst - bit))
+              {
+                continuous = false;
+                break;
+              }
+            }
+          }
+        }
+
+        if (continuous) {
+          o << "      // continuous: op" << OpOrder[Vals[i].getName()] << "\n";
+          
+          // Mask off the right bits
+          // Low mask (ie. shift, if necessary)
+          if (endBitInVar != 0) {
+            o << "      op" << OpOrder[Vals[i].getName()]
+              << " >>= endBitInVar;\n";
+            beginBitInVar -= endBitInVar;
+            endBitInVar = 0;
+          }
+
+          // High mask
+          o << "      op" << OpOrder[Vals[i].getName()]
+            << " &= (1<<" << beginBitInVar+1 << ") - 1;\n";
+
+          // Shift the value to the correct place (according to place in instr)
+          if (endBitInInst != 0)
+            o << "      op" << OpOrder[Vals[i].getName()]
+              << " <<= " << endBitInInst << ";\n";
+
+          // Just OR in the result
+          o << "      Value |= op" << OpOrder[Vals[i].getName()] << ";\n";
+        }
+
+        // otherwise, will be taken care of in the loop below using this value:
+        OpContinuous[Vals[i].getName()] = continuous;
       }
     }
 
@@ -81,18 +166,32 @@ void CodeEmitterGen::createEmitter(std::ostream &o) {
         // Scan through the field looking for bit initializers of the current
         // variable...
         for (int i = FieldInitializer->getNumBits()-1; i >= 0; --i) {
-          if (BitInit *BI=dynamic_cast<BitInit*>(FieldInitializer->getBit(i))){
+          if (BitInit *BI=dynamic_cast<BitInit*>(FieldInitializer->getBit(i)))
+          {
             o << "      // bit init: f: " << f << ", i: " << i << "\n";
-          } else if (UnsetInit *UI = 
+          } else if (UnsetInit *UI =
                      dynamic_cast<UnsetInit*>(FieldInitializer->getBit(i))) {
             o << "      // unset init: f: " << f << ", i: " << i << "\n";
           } else if (VarBitInit *VBI =
                      dynamic_cast<VarBitInit*>(FieldInitializer->getBit(i))) {
             TypedInit *TI = VBI->getVariable();
             if (VarInit *VI = dynamic_cast<VarInit*>(TI)) {
-              o << "      Value |= getValueBit(op" << OpOrder[VI->getName()]
-                << ", " << VBI->getBitNum()
-                << ")" << " << " << i << ";\n";
+              // If the bits of the field are laid out consecutively in the
+              // instruction, then instead of separately ORing in bits, just
+              // mask and shift the entire field for efficiency.
+              if (OpContinuous[VI->getName()]) {
+                // already taken care of in the loop above, thus there is no
+                // need to individually OR in the bits
+
+                // for debugging, output the regular version anyway, commented
+                o << "      // Value |= getValueBit(op"
+                  << OpOrder[VI->getName()] << ", " << VBI->getBitNum()
+                  << ")" << " << " << i << ";\n";
+              } else {
+                o << "      Value |= getValueBit(op" << OpOrder[VI->getName()]
+                  << ", " << VBI->getBitNum()
+                  << ")" << " << " << i << ";\n";
+              }
             } else if (FieldInit *FI = dynamic_cast<FieldInit*>(TI)) {
               // FIXME: implement this!
               o << "FIELD INIT not implemented yet!\n";
@@ -100,7 +199,7 @@ void CodeEmitterGen::createEmitter(std::ostream &o) {
               o << "Error: UNIMPLEMENTED\n";
             }
           }
-        } 
+        }
       } else {
         // ignore annul and predict bits since no one sets them yet
         if (Vals[f].getName() == "annul" || Vals[f].getName() == "predict") {
@@ -112,6 +211,7 @@ void CodeEmitterGen::createEmitter(std::ostream &o) {
     o << "      break;\n"
       << "    }\n";
   }
+
   o << "  default:\n"
     << "    DEBUG(std::cerr << \"Not supported instr: \" << MI << \"\\n\");\n"
     << "    abort();\n"