[llvm-commits] CVS: llvm/lib/Transforms/Scalar/InstructionCombining.cpp

[Chris Lattner]

Changes in directory llvm/lib/Transforms/Scalar:

InstructionCombining.cpp updated: 1.455 -> 1.456
---
Log message:

If we can look through vector operations to find the scalar version of an 
extract_element'd value, do so.


---
Diffs of the changes:  (+40 -0)

 InstructionCombining.cpp |   40 ++++++++++++++++++++++++++++++++++++++++
 1 files changed, 40 insertions(+)


Index: llvm/lib/Transforms/Scalar/InstructionCombining.cpp
diff -u llvm/lib/Transforms/Scalar/InstructionCombining.cpp:1.455 llvm/lib/Transforms/Scalar/InstructionCombining.cpp:1.456
--- llvm/lib/Transforms/Scalar/InstructionCombining.cpp:1.455	Fri Mar 31 12:25:14 2006
+++ llvm/lib/Transforms/Scalar/InstructionCombining.cpp	Fri Mar 31 17:01:56 2006
@@ -6654,7 +6654,41 @@
   return false;
 }
 
+/// FindScalarElement - Given a vector and an element number, see if the scalar
+/// value is already around as a register, for example if it were inserted then
+/// extracted from the vector.
+static Value *FindScalarElement(Value *V, unsigned EltNo) {
+  assert(isa<PackedType>(V->getType()) && "Not looking at a vector?");
+  const PackedType *PTy = cast<PackedType>(V->getType());
+  if (EltNo >= PTy->getNumElements())  // Out of range access.
+    return UndefValue::get(PTy->getElementType());
+  
+  if (isa<UndefValue>(V))
+    return UndefValue::get(PTy->getElementType());
+  else if (isa<ConstantAggregateZero>(V))
+    return Constant::getNullValue(PTy->getElementType());
+  else if (ConstantPacked *CP = dyn_cast<ConstantPacked>(V))
+    return CP->getOperand(EltNo);
+  else if (InsertElementInst *III = dyn_cast<InsertElementInst>(V)) {
+    // If this is an insert to a variable element, we don't know what it is.
+    if (!isa<ConstantUInt>(III->getOperand(2))) return 0;
+    unsigned IIElt = cast<ConstantUInt>(III->getOperand(2))->getValue();
+    
+    // If this is an insert to the element we are looking for, return the
+    // inserted value.
+    if (EltNo == IIElt) return III->getOperand(1);
+    
+    // Otherwise, the insertelement doesn't modify the value, recurse on its
+    // vector input.
+    return FindScalarElement(III->getOperand(0), EltNo);
+  }
+  
+  // Otherwise, we don't know.
+  return 0;
+}
+
 Instruction *InstCombiner::visitExtractElementInst(ExtractElementInst &EI) {
+
   // If packed val is undef, replace extract with scalar undef.
   if (isa<UndefValue>(EI.getOperand(0)))
     return ReplaceInstUsesWith(EI, UndefValue::get(EI.getType()));
@@ -6676,6 +6710,12 @@
       return ReplaceInstUsesWith(EI, op0);
   }
   
+  // If extracting a specified index from the vector, see if we can recursively
+  // find a previously computed scalar that was inserted into the vector.
+  if (ConstantUInt *IdxC = dyn_cast<ConstantUInt>(EI.getOperand(1)))
+    if (Value *Elt = FindScalarElement(EI.getOperand(0), IdxC->getValue()))
+      return ReplaceInstUsesWith(EI, Elt);
+  
   if (Instruction *I = dyn_cast<Instruction>(EI.getOperand(0)))
     if (I->hasOneUse()) {
       // Push extractelement into predecessor operation if legal and