Add source-level dominators analysis. Patch by Guoping Long!

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@142885 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 160 insertions, 0 deletions

diff --git a/lib/Analysis/Dominators.cpp b/lib/Analysis/Dominators.cpp
new file mode 100644
index 0000000000..62b72287f9
--- /dev/null
+++ b/lib/Analysis/Dominators.cpp
@@ -0,0 +1,160 @@
+//==- Dominators.cpp - Construct the Dominance Tree Given CFG ----*- C++ --*-==//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This file implements a simple, fast dominance algorithm for source-level CFGs.
+//
+//===----------------------------------------------------------------------===//
+
+#include "clang/Analysis/Analyses/Dominators.h"
+#include "clang/Analysis/CFG.h"
+#include "clang/Analysis/AnalysisContext.h"
+#include "clang/Analysis/Analyses/PostOrderCFGView.h"
+
+using namespace clang;
+
+DominatorTree::~DominatorTree() {
+  IDoms.clear();
+  RootNode = 0;
+}
+
+CFGBlock * DominatorTree::getNode(const CFGBlock *B) const {
+  CFGBlockMapTy::const_iterator I = IDoms.find(B);
+  return I != IDoms.end() ? I->second : 0; 
+}
+
+bool DominatorTree::properlyDominates(const CFGBlock *A, 
+                                      const CFGBlock *B) const {
+  if (0 == A || 0 == B || A == B)
+    return false;
+
+  // The EntryBlock dominates every other block.
+  if (A == RootNode)
+    return true;
+
+  // Note: The dominator of the EntryBlock is itself.
+  CFGBlock *IDom = getNode(B);
+  while (IDom != A && IDom != RootNode)
+    IDom = getNode(IDom);
+
+  return IDom != RootNode;
+}
+
+bool DominatorTree::dominates(const CFGBlock *A,
+                              const CFGBlock *B) const {
+  if (A == B)
+    return true;
+
+  return properlyDominates(A, B);
+}
+
+const CFGBlock * DominatorTree::findNearestCommonDominator
+      (const CFGBlock *A, const CFGBlock *B) const {
+  //If A dominates B, then A is the nearest common dominator
+  if (dominates(A, B))
+    return A;
+
+  //If B dominates A, then B is the nearest common dominator
+  if (dominates(B, A))
+    return B;
+
+  //Collect all A's dominators
+  llvm::SmallPtrSet<CFGBlock *, 16> ADoms;
+  ADoms.insert(RootNode);
+  CFGBlock *ADom = getNode(A);
+  while (ADom != RootNode) {
+    ADoms.insert(ADom);
+    ADom = getNode(ADom);
+  }  
+
+  //Check all B's dominators against ADoms
+  CFGBlock *BDom = getNode(B);
+  while (BDom != RootNode){
+    if (ADoms.count(BDom) != 0)
+      return BDom;
+
+    BDom = getNode(BDom);
+  }
+
+  //The RootNode dominates every other node
+  return RootNode;
+}
+
+/// Constructs immediate dominator tree for a given CFG based on the algorithm
+/// described in this paper:
+///
+///  A Simple, Fast Dominance Algorithm
+///  Keith D. Cooper, Timothy J. Harvey and Ken Kennedy
+///  Software-Practice and Expreience, 2001;4:1-10.
+///
+/// This implementation is simple and runs faster in practice than the classis
+/// Lengauer-Tarjan algorithm. For detailed discussions, refer to the paper. 
+void DominatorTree::BuildDominatorTree() {
+  CFG *cfg = AC.getCFG();
+  CFGBlock *EntryBlk = &cfg->getEntry();
+
+  //Sort all CFGBlocks in reverse order
+  PostOrderCFGView *rpocfg = AC.getAnalysis<PostOrderCFGView>();
+
+  //Set the root of the dominance tree
+  RootNode = EntryBlk;
+  
+  //Compute the immediate dominator for each CFGBlock
+  IDoms[EntryBlk] = EntryBlk;
+  bool changed = true;
+  while (changed){
+    changed = false;
+
+    for (PostOrderCFGView::iterator I = rpocfg->begin(),
+        E = rpocfg->end(); I != E; ++I){
+      if (EntryBlk == *I)
+        continue;
+      if (const CFGBlock *B = *I) {
+        //Compute immediate dominance information for CFGBlock B
+        CFGBlock *IDom = 0;
+        for (CFGBlock::const_pred_iterator J = B->pred_begin(),
+            K = B->pred_end(); J != K; ++J)
+          if( CFGBlock *P = *J) {
+            if (IDoms.find(P) == IDoms.end())
+              continue;
+            if (!IDom)
+              IDom = P;
+            else {
+              //intersect IDom and P
+              CFGBlock *B1 = IDom, *B2 = P;
+              while (B1 != B2) {
+                while ((rpocfg->getComparator())(B2,B1))
+                  B1 = IDoms[B1];
+                while ((rpocfg->getComparator())(B1,B2))
+                  B2 = IDoms[B2];
+              }
+              IDom = B1;
+            }
+          }
+        if (IDoms[B] != IDom) {
+          IDoms[B] = IDom;
+          changed = true;
+        } 
+      }
+    }
+  }//while
+}
+
+void DominatorTree::dump() {
+  CFG *cfg = AC.getCFG();
+
+  llvm::errs() << "Immediate dominance tree (Node#,IDom#):\n";
+  for (CFG::const_iterator I = cfg->begin(),
+      E = cfg->end(); I != E; ++I) {
+    assert(IDoms[(*I)] && 
+       "Failed to find the immediate dominator for all CFG blocks.");
+    llvm::errs() << "(" << (*I)->getBlockID()
+                 << "," << IDoms[(*I)]->getBlockID() << ")\n";
+  }
+}
+