1 files changed, 277 insertions, 0 deletions
diff --git a/lib/Transforms/IPO/IPConstantPropagation.cpp b/lib/Transforms/IPO/IPConstantPropagation.cpp
new file mode 100644
index 000000000000..2dc855824691
--- /dev/null
+++ b/lib/Transforms/IPO/IPConstantPropagation.cpp
@@ -0,0 +1,277 @@
+//===-- IPConstantPropagation.cpp - Propagate constants through calls -----===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This pass implements an _extremely_ simple interprocedural constant
+// propagation pass.  It could certainly be improved in many different ways,
+// like using a worklist.  This pass makes arguments dead, but does not remove
+// them.  The existing dead argument elimination pass should be run after this
+// to clean up the mess.
+//
+//===----------------------------------------------------------------------===//
+
+#define DEBUG_TYPE "ipconstprop"
+#include "llvm/Transforms/IPO.h"
+#include "llvm/Constants.h"
+#include "llvm/Instructions.h"
+#include "llvm/Module.h"
+#include "llvm/Pass.h"
+#include "llvm/Analysis/ValueTracking.h"
+#include "llvm/Support/CallSite.h"
+#include "llvm/Support/Compiler.h"
+#include "llvm/ADT/Statistic.h"
+#include "llvm/ADT/SmallVector.h"
+using namespace llvm;
+
+STATISTIC(NumArgumentsProped, "Number of args turned into constants");
+STATISTIC(NumReturnValProped, "Number of return values turned into constants");
+
+namespace {
+  /// IPCP - The interprocedural constant propagation pass
+  ///
+  struct VISIBILITY_HIDDEN IPCP : public ModulePass {
+    static char ID; // Pass identification, replacement for typeid
+    IPCP() : ModulePass(&ID) {}
+
+    bool runOnModule(Module &M);
+  private:
+    bool PropagateConstantsIntoArguments(Function &F);
+    bool PropagateConstantReturn(Function &F);
+  };
+}
+
+char IPCP::ID = 0;
+static RegisterPass<IPCP>
+X("ipconstprop", "Interprocedural constant propagation");
+
+ModulePass *llvm::createIPConstantPropagationPass() { return new IPCP(); }
+
+bool IPCP::runOnModule(Module &M) {
+  bool Changed = false;
+  bool LocalChange = true;
+
+  // FIXME: instead of using smart algorithms, we just iterate until we stop
+  // making changes.
+  while (LocalChange) {
+    LocalChange = false;
+    for (Module::iterator I = M.begin(), E = M.end(); I != E; ++I)
+      if (!I->isDeclaration()) {
+        // Delete any klingons.
+        I->removeDeadConstantUsers();
+        if (I->hasLocalLinkage())
+          LocalChange |= PropagateConstantsIntoArguments(*I);
+        Changed |= PropagateConstantReturn(*I);
+      }
+    Changed |= LocalChange;
+  }
+  return Changed;
+}
+
+/// PropagateConstantsIntoArguments - Look at all uses of the specified
+/// function.  If all uses are direct call sites, and all pass a particular
+/// constant in for an argument, propagate that constant in as the argument.
+///
+bool IPCP::PropagateConstantsIntoArguments(Function &F) {
+  if (F.arg_empty() || F.use_empty()) return false; // No arguments? Early exit.
+
+  // For each argument, keep track of its constant value and whether it is a
+  // constant or not.  The bool is driven to true when found to be non-constant.
+  SmallVector<std::pair<Constant*, bool>, 16> ArgumentConstants;
+  ArgumentConstants.resize(F.arg_size());
+
+  unsigned NumNonconstant = 0;
+  for (Value::use_iterator UI = F.use_begin(), E = F.use_end(); UI != E; ++UI) {
+    // Used by a non-instruction, or not the callee of a function, do not
+    // transform.
+    if (!isa<CallInst>(*UI) && !isa<InvokeInst>(*UI))
+      return false;
+    
+    CallSite CS = CallSite::get(cast<Instruction>(*UI));
+    if (!CS.isCallee(UI))
+      return false;
+
+    // Check out all of the potentially constant arguments.  Note that we don't
+    // inspect varargs here.
+    CallSite::arg_iterator AI = CS.arg_begin();
+    Function::arg_iterator Arg = F.arg_begin();
+    for (unsigned i = 0, e = ArgumentConstants.size(); i != e;
+         ++i, ++AI, ++Arg) {
+      
+      // If this argument is known non-constant, ignore it.
+      if (ArgumentConstants[i].second)
+        continue;
+      
+      Constant *C = dyn_cast<Constant>(*AI);
+      if (C && ArgumentConstants[i].first == 0) {
+        ArgumentConstants[i].first = C;   // First constant seen.
+      } else if (C && ArgumentConstants[i].first == C) {
+        // Still the constant value we think it is.
+      } else if (*AI == &*Arg) {
+        // Ignore recursive calls passing argument down.
+      } else {
+        // Argument became non-constant.  If all arguments are non-constant now,
+        // give up on this function.
+        if (++NumNonconstant == ArgumentConstants.size())
+          return false;
+        ArgumentConstants[i].second = true;
+      }
+    }
+  }
+
+  // If we got to this point, there is a constant argument!
+  assert(NumNonconstant != ArgumentConstants.size());
+  bool MadeChange = false;
+  Function::arg_iterator AI = F.arg_begin();
+  for (unsigned i = 0, e = ArgumentConstants.size(); i != e; ++i, ++AI) {
+    // Do we have a constant argument?
+    if (ArgumentConstants[i].second || AI->use_empty())
+      continue;
+  
+    Value *V = ArgumentConstants[i].first;
+    if (V == 0) V = UndefValue::get(AI->getType());
+    AI->replaceAllUsesWith(V);
+    ++NumArgumentsProped;
+    MadeChange = true;
+  }
+  return MadeChange;
+}
+
+
+// Check to see if this function returns one or more constants. If so, replace
+// all callers that use those return values with the constant value. This will
+// leave in the actual return values and instructions, but deadargelim will
+// clean that up.
+//
+// Additionally if a function always returns one of its arguments directly,
+// callers will be updated to use the value they pass in directly instead of
+// using the return value.
+bool IPCP::PropagateConstantReturn(Function &F) {
+  if (F.getReturnType() == Type::VoidTy)
+    return false; // No return value.
+
+  // If this function could be overridden later in the link stage, we can't
+  // propagate information about its results into callers.
+  if (F.mayBeOverridden())
+    return false;
+  
+  // Check to see if this function returns a constant.
+  SmallVector<Value *,4> RetVals;
+  const StructType *STy = dyn_cast<StructType>(F.getReturnType());
+  if (STy)
+    for (unsigned i = 0, e = STy->getNumElements(); i < e; ++i) 
+      RetVals.push_back(UndefValue::get(STy->getElementType(i)));
+  else
+    RetVals.push_back(UndefValue::get(F.getReturnType()));
+
+  unsigned NumNonConstant = 0;
+  for (Function::iterator BB = F.begin(), E = F.end(); BB != E; ++BB)
+    if (ReturnInst *RI = dyn_cast<ReturnInst>(BB->getTerminator())) {
+      for (unsigned i = 0, e = RetVals.size(); i != e; ++i) {
+        // Already found conflicting return values?
+        Value *RV = RetVals[i];
+        if (!RV)
+          continue;
+
+        // Find the returned value
+        Value *V;
+        if (!STy)
+          V = RI->getOperand(i);
+        else
+          V = FindInsertedValue(RI->getOperand(0), i);
+
+        if (V) {
+          // Ignore undefs, we can change them into anything
+          if (isa<UndefValue>(V))
+            continue;
+          
+          // Try to see if all the rets return the same constant or argument.
+          if (isa<Constant>(V) || isa<Argument>(V)) {
+            if (isa<UndefValue>(RV)) {
+              // No value found yet? Try the current one.
+              RetVals[i] = V;
+              continue;
+            }
+            // Returning the same value? Good.
+            if (RV == V)
+              continue;
+          }
+        }
+        // Different or no known return value? Don't propagate this return
+        // value.
+        RetVals[i] = 0;
+        // All values non constant? Stop looking.
+        if (++NumNonConstant == RetVals.size())
+          return false;
+      }
+    }
+
+  // If we got here, the function returns at least one constant value.  Loop
+  // over all users, replacing any uses of the return value with the returned
+  // constant.
+  bool MadeChange = false;
+  for (Value::use_iterator UI = F.use_begin(), E = F.use_end(); UI != E; ++UI) {
+    CallSite CS = CallSite::get(*UI);
+    Instruction* Call = CS.getInstruction();
+
+    // Not a call instruction or a call instruction that's not calling F
+    // directly?
+    if (!Call || !CS.isCallee(UI))
+      continue;
+    
+    // Call result not used?
+    if (Call->use_empty())
+      continue;
+
+    MadeChange = true;
+
+    if (STy == 0) {
+      Value* New = RetVals[0];
+      if (Argument *A = dyn_cast<Argument>(New))
+        // Was an argument returned? Then find the corresponding argument in
+        // the call instruction and use that.
+        New = CS.getArgument(A->getArgNo());
+      Call->replaceAllUsesWith(New);
+      continue;
+    }
+   
+    for (Value::use_iterator I = Call->use_begin(), E = Call->use_end();
+         I != E;) {
+      Instruction *Ins = dyn_cast<Instruction>(*I);
+
+      // Increment now, so we can remove the use
+      ++I;
+
+      // Not an instruction? Ignore
+      if (!Ins)
+        continue;
+
+      // Find the index of the retval to replace with
+      int index = -1;
+      if (ExtractValueInst *EV = dyn_cast<ExtractValueInst>(Ins))
+        if (EV->hasIndices())
+          index = *EV->idx_begin();
+
+      // If this use uses a specific return value, and we have a replacement,
+      // replace it.
+      if (index != -1) {
+        Value *New = RetVals[index];
+        if (New) {
+          if (Argument *A = dyn_cast<Argument>(New))
+            // Was an argument returned? Then find the corresponding argument in
+            // the call instruction and use that.
+            New = CS.getArgument(A->getArgNo());
+          Ins->replaceAllUsesWith(New);
+          Ins->eraseFromParent();
+        }
+      }
+    }
+  }
+
+  if (MadeChange) ++NumReturnValProped;
+  return MadeChange;
+}