X-Git-Url: http://demsky.eecs.uci.edu/git/?a=blobdiff_plain;f=lib%2FAnalysis%2FValueTracking.cpp;h=e7e291fb928c0312eedadd47bf2bbc50c4b34866;hb=a3ec5d6eccb0fa3746050a3d3c739bd9718b6bd0;hp=78a9c77c3fa6f989c565640dde6eb426747261d5;hpb=32a9e7a2654c4aab2e617fbe53140492b3d38066;p=oota-llvm.git

diff --git a/lib/Analysis/ValueTracking.cpp b/lib/Analysis/ValueTracking.cpp
index 78a9c77c3fa..e7e291fb928 100644
--- a/lib/Analysis/ValueTracking.cpp
+++ b/lib/Analysis/ValueTracking.cpp
@@ -15,6 +15,7 @@
 #include "llvm/Analysis/ValueTracking.h"
 #include "llvm/Constants.h"
 #include "llvm/Instructions.h"
+#include "llvm/GlobalVariable.h"
 #include "llvm/IntrinsicInst.h"
 #include "llvm/Target/TargetData.h"
 #include "llvm/Support/GetElementPtrTypeIterator.h"
@@ -755,3 +756,277 @@ bool llvm::CannotBeNegativeZero(const Value *V, unsigned Depth) {
   return false;
 }
 
+// This is the recursive version of BuildSubAggregate. It takes a few different
+// arguments. Idxs is the index within the nested struct From that we are
+// looking at now (which is of type IndexedType). IdxSkip is the number of
+// indices from Idxs that should be left out when inserting into the resulting
+// struct. To is the result struct built so far, new insertvalue instructions
+// build on that.
+Value *BuildSubAggregate(Value *From, Value* To, const Type *IndexedType,
+                                 SmallVector<unsigned, 10> &Idxs,
+                                 unsigned IdxSkip,
+                                 Instruction *InsertBefore) {
+  const llvm::StructType *STy = llvm::dyn_cast<llvm::StructType>(IndexedType);
+  if (STy) {
+    // Save the original To argument so we can modify it
+    Value *OrigTo = To;
+    // General case, the type indexed by Idxs is a struct
+    for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i) {
+      // Process each struct element recursively
+      Idxs.push_back(i);
+      Value *PrevTo = To;
+      To = BuildSubAggregate(From, To, STy->getElementType(i), Idxs, IdxSkip,
+                             InsertBefore);
+      Idxs.pop_back();
+      if (!To) {
+        // Couldn't find any inserted value for this index? Cleanup
+        while (PrevTo != OrigTo) {
+          InsertValueInst* Del = cast<InsertValueInst>(PrevTo);
+          PrevTo = Del->getAggregateOperand();
+          Del->eraseFromParent();
+        }
+        // Stop processing elements
+        break;
+      }
+    }
+    // If we succesfully found a value for each of our subaggregates 
+    if (To)
+      return To;
+  }
+  // Base case, the type indexed by SourceIdxs is not a struct, or not all of
+  // the struct's elements had a value that was inserted directly. In the latter
+  // case, perhaps we can't determine each of the subelements individually, but
+  // we might be able to find the complete struct somewhere.
+  
+  // Find the value that is at that particular spot
+  Value *V = FindInsertedValue(From, Idxs.begin(), Idxs.end());
+
+  if (!V)
+    return NULL;
+
+  // Insert the value in the new (sub) aggregrate
+  return llvm::InsertValueInst::Create(To, V, Idxs.begin() + IdxSkip,
+                                       Idxs.end(), "tmp", InsertBefore);
+}
+
+// This helper takes a nested struct and extracts a part of it (which is again a
+// struct) into a new value. For example, given the struct:
+// { a, { b, { c, d }, e } }
+// and the indices "1, 1" this returns
+// { c, d }.
+//
+// It does this by inserting an insertvalue for each element in the resulting
+// struct, as opposed to just inserting a single struct. This will only work if
+// each of the elements of the substruct are known (ie, inserted into From by an
+// insertvalue instruction somewhere).
+//
+// All inserted insertvalue instructions are inserted before InsertBefore
+Value *BuildSubAggregate(Value *From, const unsigned *idx_begin,
+                         const unsigned *idx_end, Instruction *InsertBefore) {
+  assert(InsertBefore && "Must have someplace to insert!");
+  const Type *IndexedType = ExtractValueInst::getIndexedType(From->getType(),
+                                                             idx_begin,
+                                                             idx_end);
+  Value *To = UndefValue::get(IndexedType);
+  SmallVector<unsigned, 10> Idxs(idx_begin, idx_end);
+  unsigned IdxSkip = Idxs.size();
+
+  return BuildSubAggregate(From, To, IndexedType, Idxs, IdxSkip, InsertBefore);
+}
+
+/// FindInsertedValue - Given an aggregrate and an sequence of indices, see if
+/// the scalar value indexed is already around as a register, for example if it
+/// were inserted directly into the aggregrate.
+///
+/// If InsertBefore is not null, this function will duplicate (modified)
+/// insertvalues when a part of a nested struct is extracted.
+Value *llvm::FindInsertedValue(Value *V, const unsigned *idx_begin,
+                         const unsigned *idx_end, Instruction *InsertBefore) {
+  // Nothing to index? Just return V then (this is useful at the end of our
+  // recursion)
+  if (idx_begin == idx_end)
+    return V;
+  // We have indices, so V should have an indexable type
+  assert((isa<StructType>(V->getType()) || isa<ArrayType>(V->getType()))
+         && "Not looking at a struct or array?");
+  assert(ExtractValueInst::getIndexedType(V->getType(), idx_begin, idx_end)
+         && "Invalid indices for type?");
+  const CompositeType *PTy = cast<CompositeType>(V->getType());
+  
+  if (isa<UndefValue>(V))
+    return UndefValue::get(ExtractValueInst::getIndexedType(PTy,
+                                                              idx_begin,
+                                                              idx_end));
+  else if (isa<ConstantAggregateZero>(V))
+    return Constant::getNullValue(ExtractValueInst::getIndexedType(PTy, 
+                                                                     idx_begin,
+                                                                     idx_end));
+  else if (Constant *C = dyn_cast<Constant>(V)) {
+    if (isa<ConstantArray>(C) || isa<ConstantStruct>(C))
+      // Recursively process this constant
+      return FindInsertedValue(C->getOperand(*idx_begin), ++idx_begin, idx_end,
+                               InsertBefore);
+  } else if (InsertValueInst *I = dyn_cast<InsertValueInst>(V)) {
+    // Loop the indices for the insertvalue instruction in parallel with the
+    // requested indices
+    const unsigned *req_idx = idx_begin;
+    for (const unsigned *i = I->idx_begin(), *e = I->idx_end();
+         i != e; ++i, ++req_idx) {
+      if (req_idx == idx_end) {
+        if (InsertBefore)
+          // The requested index identifies a part of a nested aggregate. Handle
+          // this specially. For example,
+          // %A = insertvalue { i32, {i32, i32 } } undef, i32 10, 1, 0
+          // %B = insertvalue { i32, {i32, i32 } } %A, i32 11, 1, 1
+          // %C = extractvalue {i32, { i32, i32 } } %B, 1
+          // This can be changed into
+          // %A = insertvalue {i32, i32 } undef, i32 10, 0
+          // %C = insertvalue {i32, i32 } %A, i32 11, 1
+          // which allows the unused 0,0 element from the nested struct to be
+          // removed.
+          return BuildSubAggregate(V, idx_begin, req_idx, InsertBefore);
+        else
+          // We can't handle this without inserting insertvalues
+          return 0;
+      }
+      
+      // This insert value inserts something else than what we are looking for.
+      // See if the (aggregrate) value inserted into has the value we are
+      // looking for, then.
+      if (*req_idx != *i)
+        return FindInsertedValue(I->getAggregateOperand(), idx_begin, idx_end,
+                                 InsertBefore);
+    }
+    // If we end up here, the indices of the insertvalue match with those
+    // requested (though possibly only partially). Now we recursively look at
+    // the inserted value, passing any remaining indices.
+    return FindInsertedValue(I->getInsertedValueOperand(), req_idx, idx_end,
+                             InsertBefore);
+  } else if (ExtractValueInst *I = dyn_cast<ExtractValueInst>(V)) {
+    // If we're extracting a value from an aggregrate that was extracted from
+    // something else, we can extract from that something else directly instead.
+    // However, we will need to chain I's indices with the requested indices.
+   
+    // Calculate the number of indices required 
+    unsigned size = I->getNumIndices() + (idx_end - idx_begin);
+    // Allocate some space to put the new indices in
+    SmallVector<unsigned, 5> Idxs;
+    Idxs.reserve(size);
+    // Add indices from the extract value instruction
+    for (const unsigned *i = I->idx_begin(), *e = I->idx_end();
+         i != e; ++i)
+      Idxs.push_back(*i);
+    
+    // Add requested indices
+    for (const unsigned *i = idx_begin, *e = idx_end; i != e; ++i)
+      Idxs.push_back(*i);
+
+    assert(Idxs.size() == size 
+           && "Number of indices added not correct?");
+    
+    return FindInsertedValue(I->getAggregateOperand(), Idxs.begin(), Idxs.end(),
+                             InsertBefore);
+  }
+  // Otherwise, we don't know (such as, extracting from a function return value
+  // or load instruction)
+  return 0;
+}
+
+/// GetConstantStringInfo - This function computes the length of a
+/// null-terminated C string pointed to by V.  If successful, it returns true
+/// and returns the string in Str.  If unsuccessful, it returns false.
+bool llvm::GetConstantStringInfo(Value *V, std::string &Str, uint64_t Offset,
+                                 bool StopAtNul) {
+  // If V is NULL then return false;
+  if (V == NULL) return false;
+
+  // Look through bitcast instructions.
+  if (BitCastInst *BCI = dyn_cast<BitCastInst>(V))
+    return GetConstantStringInfo(BCI->getOperand(0), Str, Offset, StopAtNul);
+  
+  // If the value is not a GEP instruction nor a constant expression with a
+  // GEP instruction, then return false because ConstantArray can't occur
+  // any other way
+  User *GEP = 0;
+  if (GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(V)) {
+    GEP = GEPI;
+  } else if (ConstantExpr *CE = dyn_cast<ConstantExpr>(V)) {
+    if (CE->getOpcode() == Instruction::BitCast)
+      return GetConstantStringInfo(CE->getOperand(0), Str, Offset, StopAtNul);
+    if (CE->getOpcode() != Instruction::GetElementPtr)
+      return false;
+    GEP = CE;
+  }
+  
+  if (GEP) {
+    // Make sure the GEP has exactly three arguments.
+    if (GEP->getNumOperands() != 3)
+      return false;
+    
+    // Make sure the index-ee is a pointer to array of i8.
+    const PointerType *PT = cast<PointerType>(GEP->getOperand(0)->getType());
+    const ArrayType *AT = dyn_cast<ArrayType>(PT->getElementType());
+    if (AT == 0 || AT->getElementType() != Type::Int8Ty)
+      return false;
+    
+    // Check to make sure that the first operand of the GEP is an integer and
+    // has value 0 so that we are sure we're indexing into the initializer.
+    ConstantInt *FirstIdx = dyn_cast<ConstantInt>(GEP->getOperand(1));
+    if (FirstIdx == 0 || !FirstIdx->isZero())
+      return false;
+    
+    // If the second index isn't a ConstantInt, then this is a variable index
+    // into the array.  If this occurs, we can't say anything meaningful about
+    // the string.
+    uint64_t StartIdx = 0;
+    if (ConstantInt *CI = dyn_cast<ConstantInt>(GEP->getOperand(2)))
+      StartIdx = CI->getZExtValue();
+    else
+      return false;
+    return GetConstantStringInfo(GEP->getOperand(0), Str, StartIdx+Offset,
+                                 StopAtNul);
+  }
+  
+  // The GEP instruction, constant or instruction, must reference a global
+  // variable that is a constant and is initialized. The referenced constant
+  // initializer is the array that we'll use for optimization.
+  GlobalVariable* GV = dyn_cast<GlobalVariable>(V);
+  if (!GV || !GV->isConstant() || !GV->hasInitializer())
+    return false;
+  Constant *GlobalInit = GV->getInitializer();
+  
+  // Handle the ConstantAggregateZero case
+  if (isa<ConstantAggregateZero>(GlobalInit)) {
+    // This is a degenerate case. The initializer is constant zero so the
+    // length of the string must be zero.
+    Str.clear();
+    return true;
+  }
+  
+  // Must be a Constant Array
+  ConstantArray *Array = dyn_cast<ConstantArray>(GlobalInit);
+  if (Array == 0 || Array->getType()->getElementType() != Type::Int8Ty)
+    return false;
+  
+  // Get the number of elements in the array
+  uint64_t NumElts = Array->getType()->getNumElements();
+  
+  if (Offset > NumElts)
+    return false;
+  
+  // Traverse the constant array from 'Offset' which is the place the GEP refers
+  // to in the array.
+  Str.reserve(NumElts-Offset);
+  for (unsigned i = Offset; i != NumElts; ++i) {
+    Constant *Elt = Array->getOperand(i);
+    ConstantInt *CI = dyn_cast<ConstantInt>(Elt);
+    if (!CI) // This array isn't suitable, non-int initializer.
+      return false;
+    if (StopAtNul && CI->isZero())
+      return true; // we found end of string, success!
+    Str += (char)CI->getZExtValue();
+  }
+  
+  // The array isn't null terminated, but maybe this is a memcpy, not a strcpy.
+  return true;
+}