Initial support for edge profiling

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@12225 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Transforms/Instrumentation/EdgeProfiling.cpp

@@ -0,0 +1,94 @@
+//===- EdgeProfiling.cpp - Insert counters for edge profiling -------------===//
+// 
+//                      The LLVM Compiler Infrastructure
+//
+// This file was developed by the LLVM research group and is distributed under
+// the University of Illinois Open Source License. See LICENSE.TXT for details.
+// 
+//===----------------------------------------------------------------------===//
+//
+// This pass instruments the specified program with counters for edge profiling.
+// Edge profiling can give a reasonable approximation of the hot paths through a
+// program, and is used for a wide variety of program transformations.
+//
+// Note that this implementation is very naive.  We insert a counter for *every*
+// edge in the program, instead of using control flow information to prune the
+// number of counters inserted.
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/Constants.h"
+#include "llvm/DerivedTypes.h"
+#include "llvm/Module.h"
+#include "llvm/Pass.h"
+#include "llvm/Transforms/Utils/BasicBlockUtils.h"
+#include "ProfilingUtils.h"
+#include <set>
+using namespace llvm;
+
+namespace {
+  class EdgeProfiler : public Pass {
+    bool run(Module &M);
+  };
+
+  RegisterOpt<EdgeProfiler> X("insert-edge-profiling",
+                              "Insert instrumentation for edge profiling");
+}
+
+bool EdgeProfiler::run(Module &M) {
+  Function *Main = M.getMainFunction();
+  if (Main == 0) {
+    std::cerr << "WARNING: cannot insert edge profiling into a module"
+              << " with no main function!\n";
+    return false;  // No main, no instrumentation!
+  }
+
+  std::set<BasicBlock*> BlocksToInstrument;
+  unsigned NumEdges = 0;
+  for (Module::iterator F = M.begin(), E = M.end(); F != E; ++F)
+    for (Function::iterator BB = F->begin(), E = F->end(); BB != E; ++BB) {
+      // Keep track of which blocks need to be instrumented.  We don't want to
+      // instrument blocks that are added as the result of breaking critical
+      // edges!
+      BlocksToInstrument.insert(BB);
+      NumEdges += BB->getTerminator()->getNumSuccessors();
+    }
+
+  const Type *ATy = ArrayType::get(Type::UIntTy, NumEdges);
+  GlobalVariable *Counters =
+    new GlobalVariable(ATy, false, GlobalValue::InternalLinkage,
+                       Constant::getNullValue(ATy), "EdgeProfCounters", &M);
+
+  ConstantPointerRef *CounterCPR = ConstantPointerRef::get(Counters);
+
+  // Instrument all of the edges...
+  unsigned i = 0;
+  for (Module::iterator F = M.begin(), E = M.end(); F != E; ++F)
+    for (Function::iterator BB = F->begin(), E = F->end(); BB != E; ++BB)
+      if (BlocksToInstrument.count(BB)) {  // Don't instrument inserted blocks
+        // Okay, we have to add a counter of each outgoing edge.  If the
+        // outgoing edge is not critical don't split it, just insert the counter
+        // in the source or destination of the edge.
+        TerminatorInst *TI = BB->getTerminator();
+        for (unsigned s = 0, e = TI->getNumSuccessors(); s != e; ++s) {
+          // If the edge is critical, split it.
+          SplitCriticalEdge(TI, s, this);
+
+          // Okay, we are guaranteed that the edge is no longer critical.  If we
+          // only have a single successor, insert the counter in this block,
+          // otherwise insert it in the successor block.
+          if (TI->getNumSuccessors() == 0) {
+            // Insert counter at the start of the block
+            IncrementCounterInBlock(BB, i++, CounterCPR);
+          } else {
+            // Insert counter at the start of the block
+            IncrementCounterInBlock(TI->getSuccessor(s), i++, CounterCPR);
+          }
+        }
+      }
+
+  // Add the initialization call to main.
+  InsertProfilingInitCall(Main, "llvm_start_edge_profiling", Counters);
+  return true;
+}
+