move some more cast-related stuff

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@92471 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 125 insertions, 0 deletions

diff --git a/lib/Transforms/InstCombine/InstCombineCasts.cpp b/lib/Transforms/InstCombine/InstCombineCasts.cpp
index b9ecaeaf4f..404f3b64b5 100644
--- a/lib/Transforms/InstCombine/InstCombineCasts.cpp
+++ b/lib/Transforms/InstCombine/InstCombineCasts.cpp
@@ -17,6 +17,131 @@
 using namespace llvm;
 using namespace PatternMatch;
 
+/// DecomposeSimpleLinearExpr - Analyze 'Val', seeing if it is a simple linear
+/// expression.  If so, decompose it, returning some value X, such that Val is
+/// X*Scale+Offset.
+///
+static Value *DecomposeSimpleLinearExpr(Value *Val, unsigned &Scale,
+                                        int &Offset) {
+  assert(Val->getType() == Type::getInt32Ty(Val->getContext()) && 
+         "Unexpected allocation size type!");
+  if (ConstantInt *CI = dyn_cast<ConstantInt>(Val)) {
+    Offset = CI->getZExtValue();
+    Scale  = 0;
+    return ConstantInt::get(Type::getInt32Ty(Val->getContext()), 0);
+  } else if (BinaryOperator *I = dyn_cast<BinaryOperator>(Val)) {
+    if (ConstantInt *RHS = dyn_cast<ConstantInt>(I->getOperand(1))) {
+      if (I->getOpcode() == Instruction::Shl) {
+        // This is a value scaled by '1 << the shift amt'.
+        Scale = 1U << RHS->getZExtValue();
+        Offset = 0;
+        return I->getOperand(0);
+      } else if (I->getOpcode() == Instruction::Mul) {
+        // This value is scaled by 'RHS'.
+        Scale = RHS->getZExtValue();
+        Offset = 0;
+        return I->getOperand(0);
+      } else if (I->getOpcode() == Instruction::Add) {
+        // We have X+C.  Check to see if we really have (X*C2)+C1, 
+        // where C1 is divisible by C2.
+        unsigned SubScale;
+        Value *SubVal = 
+          DecomposeSimpleLinearExpr(I->getOperand(0), SubScale, Offset);
+        Offset += RHS->getZExtValue();
+        Scale = SubScale;
+        return SubVal;
+      }
+    }
+  }
+
+  // Otherwise, we can't look past this.
+  Scale = 1;
+  Offset = 0;
+  return Val;
+}
+
+/// PromoteCastOfAllocation - If we find a cast of an allocation instruction,
+/// try to eliminate the cast by moving the type information into the alloc.
+Instruction *InstCombiner::PromoteCastOfAllocation(BitCastInst &CI,
+                                                   AllocaInst &AI) {
+  // This requires TargetData to get the alloca alignment and size information.
+  if (!TD) return 0;
+
+  const PointerType *PTy = cast<PointerType>(CI.getType());
+  
+  BuilderTy AllocaBuilder(*Builder);
+  AllocaBuilder.SetInsertPoint(AI.getParent(), &AI);
+
+  // Get the type really allocated and the type casted to.
+  const Type *AllocElTy = AI.getAllocatedType();
+  const Type *CastElTy = PTy->getElementType();
+  if (!AllocElTy->isSized() || !CastElTy->isSized()) return 0;
+
+  unsigned AllocElTyAlign = TD->getABITypeAlignment(AllocElTy);
+  unsigned CastElTyAlign = TD->getABITypeAlignment(CastElTy);
+  if (CastElTyAlign < AllocElTyAlign) return 0;
+
+  // If the allocation has multiple uses, only promote it if we are strictly
+  // increasing the alignment of the resultant allocation.  If we keep it the
+  // same, we open the door to infinite loops of various kinds.  (A reference
+  // from a dbg.declare doesn't count as a use for this purpose.)
+  if (!AI.hasOneUse() && !hasOneUsePlusDeclare(&AI) &&
+      CastElTyAlign == AllocElTyAlign) return 0;
+
+  uint64_t AllocElTySize = TD->getTypeAllocSize(AllocElTy);
+  uint64_t CastElTySize = TD->getTypeAllocSize(CastElTy);
+  if (CastElTySize == 0 || AllocElTySize == 0) return 0;
+
+  // See if we can satisfy the modulus by pulling a scale out of the array
+  // size argument.
+  unsigned ArraySizeScale;
+  int ArrayOffset;
+  Value *NumElements = // See if the array size is a decomposable linear expr.
+    DecomposeSimpleLinearExpr(AI.getOperand(0), ArraySizeScale, ArrayOffset);
+ 
+  // If we can now satisfy the modulus, by using a non-1 scale, we really can
+  // do the xform.
+  if ((AllocElTySize*ArraySizeScale) % CastElTySize != 0 ||
+      (AllocElTySize*ArrayOffset   ) % CastElTySize != 0) return 0;
+
+  unsigned Scale = (AllocElTySize*ArraySizeScale)/CastElTySize;
+  Value *Amt = 0;
+  if (Scale == 1) {
+    Amt = NumElements;
+  } else {
+    Amt = ConstantInt::get(Type::getInt32Ty(CI.getContext()), Scale);
+    // Insert before the alloca, not before the cast.
+    Amt = AllocaBuilder.CreateMul(Amt, NumElements, "tmp");
+  }
+  
+  if (int Offset = (AllocElTySize*ArrayOffset)/CastElTySize) {
+    Value *Off = ConstantInt::get(Type::getInt32Ty(CI.getContext()),
+                                  Offset, true);
+    Amt = AllocaBuilder.CreateAdd(Amt, Off, "tmp");
+  }
+  
+  AllocaInst *New = AllocaBuilder.CreateAlloca(CastElTy, Amt);
+  New->setAlignment(AI.getAlignment());
+  New->takeName(&AI);
+  
+  // If the allocation has one real use plus a dbg.declare, just remove the
+  // declare.
+  if (DbgDeclareInst *DI = hasOneUsePlusDeclare(&AI)) {
+    EraseInstFromFunction(*(Instruction*)DI);
+  }
+  // If the allocation has multiple real uses, insert a cast and change all
+  // things that used it to use the new cast.  This will also hack on CI, but it
+  // will die soon.
+  else if (!AI.hasOneUse()) {
+    // New is the allocation instruction, pointer typed. AI is the original
+    // allocation instruction, also pointer typed. Thus, cast to use is BitCast.
+    Value *NewCast = AllocaBuilder.CreateBitCast(New, AI.getType(), "tmpcast");
+    AI.replaceAllUsesWith(NewCast);
+  }
+  return ReplaceInstUsesWith(CI, New);
+}
+
+
 /// CanEvaluateInDifferentType - Return true if we can take the specified value
 /// and return it as type Ty without inserting any new casts and without
 /// changing the computed value.  This is used by code that tries to decide