* Implement dominator based loop identification

* Implement cleaner induction variable identification


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@1359 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 81 insertions, 0 deletions

diff --git a/lib/Analysis/LoopInfo.cpp b/lib/Analysis/LoopInfo.cpp
new file mode 100644
index 0000000000..a240ec8b8b
--- /dev/null
+++ b/lib/Analysis/LoopInfo.cpp
@@ -0,0 +1,81 @@
+//===- LoopInfo.cpp - Natural Loop Calculator -------------------------------=//
+//
+// This file defines the LoopInfo class that is used to identify natural loops
+// and determine the loop depth of various nodes of the CFG.  Note that the
+// loops identified may actually be several natural loops that share the same
+// header node... not just a single natural loop.
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/Analysis/LoopInfo.h"
+#include "llvm/Analysis/Dominators.h"
+#include "llvm/Support/DepthFirstIterator.h"
+#include "llvm/BasicBlock.h"
+#include <algorithm>
+
+bool cfg::Loop::contains(const BasicBlock *BB) const {
+  return find(Blocks.begin(), Blocks.end(), BB) != Blocks.end();
+}
+
+cfg::LoopInfo::LoopInfo(const DominatorSet &DS) {
+  const BasicBlock *RootNode = DS.getRoot();
+
+  for (df_iterator<const BasicBlock*> NI = df_begin(RootNode),
+	 NE = df_end(RootNode); NI != NE; ++NI)
+    if (Loop *L = ConsiderForLoop(*NI, DS))
+      TopLevelLoops.push_back(L);
+
+  for (unsigned i = 0; i < TopLevelLoops.size(); ++i)
+    TopLevelLoops[i]->setLoopDepth(1);
+}
+
+cfg::Loop *cfg::LoopInfo::ConsiderForLoop(const BasicBlock *BB,
+					  const DominatorSet &DS) {
+  if (BBMap.find(BB) != BBMap.end()) return 0;   // Havn't processed this node?
+
+  vector<const BasicBlock *> TodoStack;
+
+  // Scan the predecessors of BB, checking to see if BB dominates any of
+  // them.
+  for (BasicBlock::pred_const_iterator I = BB->pred_begin(),
+	 E = BB->pred_end(); I != E; ++I)
+    if (DS.dominates(BB, *I))   // If BB dominates it's predecessor...
+      TodoStack.push_back(*I);
+
+  if (TodoStack.empty()) return 0;  // Doesn't dominate any predecessors...
+
+  // Create a new loop to represent this basic block...
+  Loop *L = new Loop(BB);
+  BBMap[BB] = L;
+
+  while (!TodoStack.empty()) {  // Process all the nodes in the loop
+    const BasicBlock *X = TodoStack.back();
+    TodoStack.pop_back();
+
+    if (!L->contains(X)) {                  // As of yet unprocessed??
+      L->Blocks.push_back(X);
+
+      // Add all of the predecessors of X to the end of the work stack...
+      TodoStack.insert(TodoStack.end(), X->pred_begin(), X->pred_end());
+    }
+  }
+
+  // Add the basic blocks that comprise this loop to the BBMap so that this
+  // loop can be found for them.  Also check subsidary basic blocks to see if
+  // they start subloops of their own.
+  //
+  for (vector<const BasicBlock*>::reverse_iterator I = L->Blocks.rbegin(),
+	 E = L->Blocks.rend(); I != E; ++I) {
+
+    // Check to see if this block starts a new loop
+    if (Loop *NewLoop = ConsiderForLoop(*I, DS)) {
+      L->SubLoops.push_back(NewLoop);
+      NewLoop->ParentLoop = L;
+    }
+  
+    if (BBMap.find(*I) == BBMap.end())
+      BBMap.insert(make_pair(*I, L));
+  }
+
+  return L;
+}