1 files changed, 391 insertions, 0 deletions
diff --git a/contrib/llvm/lib/Transforms/IPO/FunctionAttrs.cpp b/contrib/llvm/lib/Transforms/IPO/FunctionAttrs.cpp
new file mode 100644
index 0000000..9bd7af6
--- /dev/null
+++ b/contrib/llvm/lib/Transforms/IPO/FunctionAttrs.cpp
@@ -0,0 +1,391 @@
+//===- FunctionAttrs.cpp - Pass which marks functions readnone or readonly ===//
+//
+//                     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 interprocedural pass which walks the
+// call-graph, looking for functions which do not access or only read
+// non-local memory, and marking them readnone/readonly.  In addition,
+// it marks function arguments (of pointer type) 'nocapture' if a call
+// to the function does not create any copies of the pointer value that
+// outlive the call.  This more or less means that the pointer is only
+// dereferenced, and not returned from the function or stored in a global.
+// This pass is implemented as a bottom-up traversal of the call-graph.
+//
+//===----------------------------------------------------------------------===//
+
+#define DEBUG_TYPE "functionattrs"
+#include "llvm/Transforms/IPO.h"
+#include "llvm/CallGraphSCCPass.h"
+#include "llvm/GlobalVariable.h"
+#include "llvm/IntrinsicInst.h"
+#include "llvm/Analysis/AliasAnalysis.h"
+#include "llvm/Analysis/CallGraph.h"
+#include "llvm/Analysis/CaptureTracking.h"
+#include "llvm/Analysis/MemoryBuiltins.h"
+#include "llvm/ADT/SmallSet.h"
+#include "llvm/ADT/Statistic.h"
+#include "llvm/ADT/UniqueVector.h"
+#include "llvm/Support/InstIterator.h"
+using namespace llvm;
+
+STATISTIC(NumReadNone, "Number of functions marked readnone");
+STATISTIC(NumReadOnly, "Number of functions marked readonly");
+STATISTIC(NumNoCapture, "Number of arguments marked nocapture");
+STATISTIC(NumNoAlias, "Number of function returns marked noalias");
+
+namespace {
+  struct FunctionAttrs : public CallGraphSCCPass {
+    static char ID; // Pass identification, replacement for typeid
+    FunctionAttrs() : CallGraphSCCPass(&ID) {}
+
+    // runOnSCC - Analyze the SCC, performing the transformation if possible.
+    bool runOnSCC(CallGraphSCC &SCC);
+
+    // AddReadAttrs - Deduce readonly/readnone attributes for the SCC.
+    bool AddReadAttrs(const CallGraphSCC &SCC);
+
+    // AddNoCaptureAttrs - Deduce nocapture attributes for the SCC.
+    bool AddNoCaptureAttrs(const CallGraphSCC &SCC);
+
+    // IsFunctionMallocLike - Does this function allocate new memory?
+    bool IsFunctionMallocLike(Function *F,
+                              SmallPtrSet<Function*, 8> &) const;
+
+    // AddNoAliasAttrs - Deduce noalias attributes for the SCC.
+    bool AddNoAliasAttrs(const CallGraphSCC &SCC);
+
+    virtual void getAnalysisUsage(AnalysisUsage &AU) const {
+      AU.setPreservesCFG();
+      CallGraphSCCPass::getAnalysisUsage(AU);
+    }
+
+    bool PointsToLocalMemory(Value *V);
+  };
+}
+
+char FunctionAttrs::ID = 0;
+static RegisterPass<FunctionAttrs>
+X("functionattrs", "Deduce function attributes");
+
+Pass *llvm::createFunctionAttrsPass() { return new FunctionAttrs(); }
+
+
+/// PointsToLocalMemory - Returns whether the given pointer value points to
+/// memory that is local to the function.  Global constants are considered
+/// local to all functions.
+bool FunctionAttrs::PointsToLocalMemory(Value *V) {
+  SmallVector<Value*, 16> Worklist;
+  unsigned MaxLookup = 8;
+
+  Worklist.push_back(V);
+
+  do {
+    V = Worklist.pop_back_val()->getUnderlyingObject();
+
+    // An alloca instruction defines local memory.
+    if (isa<AllocaInst>(V))
+      continue;
+
+    // A global constant counts as local memory for our purposes.
+    if (GlobalVariable *GV = dyn_cast<GlobalVariable>(V)) {
+      if (!GV->isConstant())
+        return false;
+      continue;
+    }
+
+    // If both select values point to local memory, then so does the select.
+    if (SelectInst *SI = dyn_cast<SelectInst>(V)) {
+      Worklist.push_back(SI->getTrueValue());
+      Worklist.push_back(SI->getFalseValue());
+      continue;
+    }
+
+    // If all values incoming to a phi node point to local memory, then so does
+    // the phi.
+    if (PHINode *PN = dyn_cast<PHINode>(V)) {
+      // Don't bother inspecting phi nodes with many operands.
+      if (PN->getNumIncomingValues() > MaxLookup)
+        return false;
+      for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
+        Worklist.push_back(PN->getIncomingValue(i));
+      continue;
+    }
+
+    return false;
+  } while (!Worklist.empty() && --MaxLookup);
+
+  return Worklist.empty();
+}
+
+/// AddReadAttrs - Deduce readonly/readnone attributes for the SCC.
+bool FunctionAttrs::AddReadAttrs(const CallGraphSCC &SCC) {
+  SmallPtrSet<Function*, 8> SCCNodes;
+
+  // Fill SCCNodes with the elements of the SCC.  Used for quickly
+  // looking up whether a given CallGraphNode is in this SCC.
+  for (CallGraphSCC::iterator I = SCC.begin(), E = SCC.end(); I != E; ++I)
+    SCCNodes.insert((*I)->getFunction());
+
+  // Check if any of the functions in the SCC read or write memory.  If they
+  // write memory then they can't be marked readnone or readonly.
+  bool ReadsMemory = false;
+  for (CallGraphSCC::iterator I = SCC.begin(), E = SCC.end(); I != E; ++I) {
+    Function *F = (*I)->getFunction();
+
+    if (F == 0)
+      // External node - may write memory.  Just give up.
+      return false;
+
+    if (F->doesNotAccessMemory())
+      // Already perfect!
+      continue;
+
+    // Definitions with weak linkage may be overridden at linktime with
+    // something that writes memory, so treat them like declarations.
+    if (F->isDeclaration() || F->mayBeOverridden()) {
+      if (!F->onlyReadsMemory())
+        // May write memory.  Just give up.
+        return false;
+
+      ReadsMemory = true;
+      continue;
+    }
+
+    // Scan the function body for instructions that may read or write memory.
+    for (inst_iterator II = inst_begin(F), E = inst_end(F); II != E; ++II) {
+      Instruction *I = &*II;
+
+      // Some instructions can be ignored even if they read or write memory.
+      // Detect these now, skipping to the next instruction if one is found.
+      CallSite CS = CallSite::get(I);
+      if (CS.getInstruction() && CS.getCalledFunction()) {
+        // Ignore calls to functions in the same SCC.
+        if (SCCNodes.count(CS.getCalledFunction()))
+          continue;
+        // Ignore intrinsics that only access local memory.
+        if (unsigned id = CS.getCalledFunction()->getIntrinsicID())
+          if (AliasAnalysis::getModRefBehavior(id) ==
+              AliasAnalysis::AccessesArguments) {
+            // Check that all pointer arguments point to local memory.
+            for (CallSite::arg_iterator CI = CS.arg_begin(), CE = CS.arg_end();
+                 CI != CE; ++CI) {
+              Value *Arg = *CI;
+              if (Arg->getType()->isPointerTy() && !PointsToLocalMemory(Arg))
+                // Writes memory.  Just give up.
+                return false;
+            }
+            // Only reads and writes local memory.
+            continue;
+          }
+      } else if (LoadInst *LI = dyn_cast<LoadInst>(I)) {
+        // Ignore loads from local memory.
+        if (PointsToLocalMemory(LI->getPointerOperand()))
+          continue;
+      } else if (StoreInst *SI = dyn_cast<StoreInst>(I)) {
+        // Ignore stores to local memory.
+        if (PointsToLocalMemory(SI->getPointerOperand()))
+          continue;
+      }
+
+      // Any remaining instructions need to be taken seriously!  Check if they
+      // read or write memory.
+      if (I->mayWriteToMemory())
+        // Writes memory.  Just give up.
+        return false;
+
+      if (isMalloc(I))
+        // malloc claims not to write memory!  PR3754.
+        return false;
+
+      // If this instruction may read memory, remember that.
+      ReadsMemory |= I->mayReadFromMemory();
+    }
+  }
+
+  // Success!  Functions in this SCC do not access memory, or only read memory.
+  // Give them the appropriate attribute.
+  bool MadeChange = false;
+  for (CallGraphSCC::iterator I = SCC.begin(), E = SCC.end(); I != E; ++I) {
+    Function *F = (*I)->getFunction();
+
+    if (F->doesNotAccessMemory())
+      // Already perfect!
+      continue;
+
+    if (F->onlyReadsMemory() && ReadsMemory)
+      // No change.
+      continue;
+
+    MadeChange = true;
+
+    // Clear out any existing attributes.
+    F->removeAttribute(~0, Attribute::ReadOnly | Attribute::ReadNone);
+
+    // Add in the new attribute.
+    F->addAttribute(~0, ReadsMemory? Attribute::ReadOnly : Attribute::ReadNone);
+
+    if (ReadsMemory)
+      ++NumReadOnly;
+    else
+      ++NumReadNone;
+  }
+
+  return MadeChange;
+}
+
+/// AddNoCaptureAttrs - Deduce nocapture attributes for the SCC.
+bool FunctionAttrs::AddNoCaptureAttrs(const CallGraphSCC &SCC) {
+  bool Changed = false;
+
+  // Check each function in turn, determining which pointer arguments are not
+  // captured.
+  for (CallGraphSCC::iterator I = SCC.begin(), E = SCC.end(); I != E; ++I) {
+    Function *F = (*I)->getFunction();
+
+    if (F == 0)
+      // External node - skip it;
+      continue;
+
+    // Definitions with weak linkage may be overridden at linktime with
+    // something that writes memory, so treat them like declarations.
+    if (F->isDeclaration() || F->mayBeOverridden())
+      continue;
+
+    for (Function::arg_iterator A = F->arg_begin(), E = F->arg_end(); A!=E; ++A)
+      if (A->getType()->isPointerTy() && !A->hasNoCaptureAttr() &&
+          !PointerMayBeCaptured(A, true, /*StoreCaptures=*/false)) {
+        A->addAttr(Attribute::NoCapture);
+        ++NumNoCapture;
+        Changed = true;
+      }
+  }
+
+  return Changed;
+}
+
+/// IsFunctionMallocLike - A function is malloc-like if it returns either null
+/// or a pointer that doesn't alias any other pointer visible to the caller.
+bool FunctionAttrs::IsFunctionMallocLike(Function *F,
+                              SmallPtrSet<Function*, 8> &SCCNodes) const {
+  UniqueVector<Value *> FlowsToReturn;
+  for (Function::iterator I = F->begin(), E = F->end(); I != E; ++I)
+    if (ReturnInst *Ret = dyn_cast<ReturnInst>(I->getTerminator()))
+      FlowsToReturn.insert(Ret->getReturnValue());
+
+  for (unsigned i = 0; i != FlowsToReturn.size(); ++i) {
+    Value *RetVal = FlowsToReturn[i+1];   // UniqueVector[0] is reserved.
+
+    if (Constant *C = dyn_cast<Constant>(RetVal)) {
+      if (!C->isNullValue() && !isa<UndefValue>(C))
+        return false;
+
+      continue;
+    }
+
+    if (isa<Argument>(RetVal))
+      return false;
+
+    if (Instruction *RVI = dyn_cast<Instruction>(RetVal))
+      switch (RVI->getOpcode()) {
+        // Extend the analysis by looking upwards.
+        case Instruction::BitCast:
+        case Instruction::GetElementPtr:
+          FlowsToReturn.insert(RVI->getOperand(0));
+          continue;
+        case Instruction::Select: {
+          SelectInst *SI = cast<SelectInst>(RVI);
+          FlowsToReturn.insert(SI->getTrueValue());
+          FlowsToReturn.insert(SI->getFalseValue());
+          continue;
+        }
+        case Instruction::PHI: {
+          PHINode *PN = cast<PHINode>(RVI);
+          for (int i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
+            FlowsToReturn.insert(PN->getIncomingValue(i));
+          continue;
+        }
+
+        // Check whether the pointer came from an allocation.
+        case Instruction::Alloca:
+          break;
+        case Instruction::Call:
+        case Instruction::Invoke: {
+          CallSite CS(RVI);
+          if (CS.paramHasAttr(0, Attribute::NoAlias))
+            break;
+          if (CS.getCalledFunction() &&
+              SCCNodes.count(CS.getCalledFunction()))
+            break;
+        } // fall-through
+        default:
+          return false;  // Did not come from an allocation.
+      }
+
+    if (PointerMayBeCaptured(RetVal, false, /*StoreCaptures=*/false))
+      return false;
+  }
+
+  return true;
+}
+
+/// AddNoAliasAttrs - Deduce noalias attributes for the SCC.
+bool FunctionAttrs::AddNoAliasAttrs(const CallGraphSCC &SCC) {
+  SmallPtrSet<Function*, 8> SCCNodes;
+
+  // Fill SCCNodes with the elements of the SCC.  Used for quickly
+  // looking up whether a given CallGraphNode is in this SCC.
+  for (CallGraphSCC::iterator I = SCC.begin(), E = SCC.end(); I != E; ++I)
+    SCCNodes.insert((*I)->getFunction());
+
+  // Check each function in turn, determining which functions return noalias
+  // pointers.
+  for (CallGraphSCC::iterator I = SCC.begin(), E = SCC.end(); I != E; ++I) {
+    Function *F = (*I)->getFunction();
+
+    if (F == 0)
+      // External node - skip it;
+      return false;
+
+    // Already noalias.
+    if (F->doesNotAlias(0))
+      continue;
+
+    // Definitions with weak linkage may be overridden at linktime, so
+    // treat them like declarations.
+    if (F->isDeclaration() || F->mayBeOverridden())
+      return false;
+
+    // We annotate noalias return values, which are only applicable to 
+    // pointer types.
+    if (!F->getReturnType()->isPointerTy())
+      continue;
+
+    if (!IsFunctionMallocLike(F, SCCNodes))
+      return false;
+  }
+
+  bool MadeChange = false;
+  for (CallGraphSCC::iterator I = SCC.begin(), E = SCC.end(); I != E; ++I) {
+    Function *F = (*I)->getFunction();
+    if (F->doesNotAlias(0) || !F->getReturnType()->isPointerTy())
+      continue;
+
+    F->setDoesNotAlias(0);
+    ++NumNoAlias;
+    MadeChange = true;
+  }
+
+  return MadeChange;
+}
+
+bool FunctionAttrs::runOnSCC(CallGraphSCC &SCC) {
+  bool Changed = AddReadAttrs(SCC);
+  Changed |= AddNoCaptureAttrs(SCC);
+  Changed |= AddNoAliasAttrs(SCC);
+  return Changed;
+}