From: yeom <yeom>
Date: Sat, 18 Jun 2011 02:04:30 +0000 (+0000)
Subject: start implementing loop termination analysis: for the initial version, checking wheth... 
X-Git-Url: http://demsky.eecs.uci.edu/git/?a=commitdiff_plain;h=55cd80c7978ca9305e3bb1ccd2b7854a921a46de;p=IRC.git

start implementing loop termination analysis: for the initial version, checking whether induction variable is getting bigger and loop guard condition is composed only with induction variables and loop invariant.
---

diff --git a/Robust/src/Analysis/Loops/LoopTerminate.java b/Robust/src/Analysis/Loops/LoopTerminate.java
new file mode 100644
index 00000000..62ab5f64
--- /dev/null
+++ b/Robust/src/Analysis/Loops/LoopTerminate.java
@@ -0,0 +1,201 @@
+package Analysis.Loops;
+
+import java.util.HashSet;
+import java.util.Iterator;
+import java.util.Set;
+
+import IR.FieldDescriptor;
+import IR.Operation;
+import IR.TypeDescriptor;
+import IR.Flat.FKind;
+import IR.Flat.FlatCondBranch;
+import IR.Flat.FlatLiteralNode;
+import IR.Flat.FlatMethod;
+import IR.Flat.FlatNode;
+import IR.Flat.FlatOpNode;
+import IR.Flat.TempDescriptor;
+
+public class LoopTerminate {
+
+  LoopInvariant loopInv;
+  Set<TempDescriptor> inductionSet;
+
+  public void terminateAnalysis(FlatMethod fm, LoopInvariant loopInv) {
+    this.loopInv = loopInv;
+    this.inductionSet = new HashSet<TempDescriptor>();
+    Loops loopFinder = loopInv.root;
+    if (loopFinder.nestedLoops().size() > 0) {
+      for (Iterator lpit = loopFinder.nestedLoops().iterator(); lpit.hasNext();) {
+        Loops loop = (Loops) lpit.next();
+        Set entrances = loop.loopEntrances();
+        processLoop(loop, loopInv);
+      }
+    }
+  }
+
+  public void processLoop(Loops l, LoopInvariant loopInv) {
+
+    boolean changed = true;
+
+    Set elements = l.loopIncElements();
+    Set toprocess = l.loopIncElements();
+    Set entrances = l.loopEntrances();
+    assert entrances.size() == 1;
+    FlatNode entrance = (FlatNode) entrances.iterator().next();
+
+    // find out basic induction variable
+    // variable i is a basic induction variable in loop if the only definitions
+    // of i within L are of the form i=i+c or i=i-c where c is loop invariant
+    for (Iterator elit = elements.iterator(); elit.hasNext();) {
+      FlatNode fn = (FlatNode) elit.next();
+      if (fn.kind() == FKind.FlatOpNode) {
+        FlatOpNode fon = (FlatOpNode) fn;
+        int op = fon.getOp().getOp();
+        if (op == Operation.ADD || op == Operation.SUB) {
+          TempDescriptor tdLeft = fon.getLeft();
+          TempDescriptor tdRight = fon.getRight();
+
+          boolean isLeftLoopInvariant = isLoopInvariant(l, fn, tdLeft);
+          boolean isRightLoopInvariant = isLoopInvariant(l, fn, tdRight);
+
+          if (isLeftLoopInvariant ^ isRightLoopInvariant) {
+
+            TempDescriptor candidateTemp;
+
+            if (isLeftLoopInvariant) {
+              candidateTemp = tdRight;
+            } else {
+              candidateTemp = tdLeft;
+            }
+
+            Set<FlatNode> defSet = loopInv.usedef.defMap(fn, candidateTemp);
+            Set<FlatNode> defSetOfLoop = new HashSet<FlatNode>();
+            for (Iterator iterator = defSet.iterator(); iterator.hasNext();) {
+              FlatNode defFlatNode = (FlatNode) iterator.next();
+              if (elements.contains(defFlatNode)) {
+                defSetOfLoop.add(defFlatNode);
+              }
+            }
+
+            if (defSetOfLoop.size() == 1) {
+              FlatNode defFn = defSet.iterator().next();
+              inductionSet.add(candidateTemp);
+            }
+
+          }
+
+        }
+      }
+    }
+
+    for (Iterator elit = elements.iterator(); elit.hasNext();) {
+      FlatNode fn = (FlatNode) elit.next();
+      if (fn.kind() == FKind.FlatCondBranch) {
+        FlatCondBranch fcb = (FlatCondBranch) fn;
+        if (fcb.isLoopBranch()) {
+
+          Set<FlatNode> condSet = getDefinitionInsideLoop(fn, fcb.getTest(), elements);
+          assert condSet.size() == 1;
+          FlatNode condFn = condSet.iterator().next();
+          if (condFn instanceof FlatOpNode) {
+            FlatOpNode condOp = (FlatOpNode) condFn;
+            // check if guard condition is composed only with induction
+            // variables
+            checkConditionNode(condOp, elements);
+          }
+
+        }
+      }
+
+    }
+
+  }
+
+  private boolean checkConditionNode(FlatOpNode fon, Set loopElements) {
+    // check flatOpNode that computes loop guard condition
+    // currently we assume that induction variable is always getting bigger
+    // and guard variable is constant
+    // so need to check (1) left operand should be induction variable
+    // (2) right operand should be constant or loop invariant
+
+    TempDescriptor left = fon.getLeft();
+    TempDescriptor right = fon.getRight();
+
+    // if (inductionSet.contains(left)) {
+    // induction = left;
+    // guard=right;
+    // } else if (inductionSet.contains(right)) {
+    // induction = right;
+    // guard=left;
+    // }
+
+    TempDescriptor induction = null;
+    TempDescriptor guard = null;
+
+    if (inductionSet.contains(left)) {
+      induction = left;
+      guard = right;
+    } else {
+      // TODO
+      // throw new Error("Loop termination error.");
+    }
+
+    if (guard != null) {
+      Set guardDefSet = getDefinitionInsideLoop(fon, guard, loopElements);
+      for (Iterator iterator = guardDefSet.iterator(); iterator.hasNext();) {
+        FlatNode guardDef = (FlatNode) iterator.next();
+        if (!(guardDef instanceof FlatLiteralNode) && !loopInv.hoisted.contains(guardDef)) {
+          // TODO
+          // throw new Error("Loop termination error.");
+        }
+      }
+    }
+
+    return true;
+  }
+
+  private boolean isLoopInvariant(Loops l, FlatNode fn, TempDescriptor td) {
+
+    Set elements = l.loopIncElements();
+    Set<FlatNode> defset = loopInv.usedef.defMap(fn, td);
+
+    Set<FlatNode> defSetOfLoop = new HashSet<FlatNode>();
+    for (Iterator<FlatNode> defit = defset.iterator(); defit.hasNext();) {
+      FlatNode def = defit.next();
+      if (elements.contains(def)) {
+        defSetOfLoop.add(def);
+      }
+    }
+
+    if (defSetOfLoop.size() == 0) {
+      // all definition comes from outside the loop
+      return true;
+    } else if (defSetOfLoop.size() == 1) {
+      // check if def is 1) constant node or 2) loop invariant
+      FlatNode defFlatNode = defSetOfLoop.iterator().next();
+      if (defFlatNode instanceof FlatLiteralNode || loopInv.hoisted.contains(defFlatNode)) {
+        return true;
+      }
+    }
+
+    return false;
+
+  }
+
+  private Set<FlatNode> getDefinitionInsideLoop(FlatNode fn, TempDescriptor td, Set loopElements) {
+
+    Set<FlatNode> defSetOfLoop = new HashSet<FlatNode>();
+
+    Set defSet = loopInv.usedef.defMap(fn, td);
+    for (Iterator iterator = defSet.iterator(); iterator.hasNext();) {
+      FlatNode defFlatNode = (FlatNode) iterator.next();
+      if (loopElements.contains(defFlatNode)) {
+        defSetOfLoop.add(defFlatNode);
+      }
+    }
+
+    return defSetOfLoop;
+
+  }
+
+}