Add new BreakCriticalEdges pass

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@3903 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 52 insertions, 0 deletions

diff --git a/lib/Transforms/Utils/BreakCriticalEdges.cpp b/lib/Transforms/Utils/BreakCriticalEdges.cpp
new file mode 100644
index 0000000000..2222a04e1d
--- /dev/null
+++ b/lib/Transforms/Utils/BreakCriticalEdges.cpp
@@ -0,0 +1,52 @@
+//===- BreakCriticalEdges.cpp - Critical Edge Elimination Pass ------------===//
+//
+// BreakCriticalEdges pass - Break all of the critical edges in the CFG by
+// inserting a dummy basic block.  This pass may be "required" by passes that
+// cannot deal with critical edges.  For this usage, the structure type is
+// forward declared.  This pass obviously invalidates the CFG, but can update
+// forward dominator (set, immediate dominators, and tree) information.
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/Transforms/Scalar.h"
+#include "llvm/Transforms/Utils/Local.h"
+#include "llvm/Analysis/Dominators.h"
+#include "llvm/Function.h"
+#include "llvm/InstrTypes.h"
+#include "Support/StatisticReporter.h"
+
+static Statistic<> NumBroken("break-crit-edges\t- Number of blocks inserted");
+
+class BreakCriticalEdges : public FunctionPass {
+public:
+  virtual bool runOnFunction(Function &F);
+
+  virtual void getAnalysisUsage(AnalysisUsage &AU) const {
+    AU.addPreserved<DominatorSet>();
+    AU.addPreserved<ImmediateDominators>();
+    AU.addPreserved<DominatorTree>();
+  }
+};
+
+static RegisterOpt<BreakCriticalEdges> X("break-crit-edges",
+                                         "Break critical edges in CFG");
+
+Pass *createBreakCriticalEdgesPass() { return new BreakCriticalEdges(); }
+
+// runOnFunction - Loop over all of the edges in the CFG, breaking critical
+// edges as they are found.
+//
+bool BreakCriticalEdges::runOnFunction(Function &F) {
+  bool Changed = false;
+  for (Function::iterator I = F.begin(), E = F.end(); I != E; ++I) {
+    TerminatorInst *TI = I->getTerminator();
+    for (unsigned i = 0, e = TI->getNumSuccessors(); i != e; ++i)
+      if (isCriticalEdge(TI, i)) {
+        SplitCriticalEdge(TI, i, this);
+        ++NumBroken;
+        Changed = true;
+      }
+  }
+
+  return Changed;
+}