CostModel: Add parameter to instruction cost to further classify operand values

On certain architectures we can support efficient vectorized version of
instructions if the operand value is uniform (splat) or a constant scalar.
An example of this is a vector shift on x86.

We can efficiently support

for (i = 0 ; i < ; i += 4)
  w[0:3] = v[0:3] << <2, 2, 2, 2>

but not

for (i = 0; i < ; i += 4)
  w[0:3] = v[0:3] << x[0:3]

This patch adds a parameter to getArithmeticInstrCost to further qualify operand
values as uniform or uniform constant.

Targets can then choose to return a different cost for instructions with such
operand values.

A follow-up commit will test this feature on x86.

radar://13576547

llvm-svn: 178807

1 files changed, 23 insertions, 1 deletions

diff --git a/llvm/lib/Analysis/CostModel.cpp b/llvm/lib/Analysis/CostModel.cpp
index df70d157b41..98a7780ad9a 100644
--- a/llvm/lib/Analysis/CostModel.cpp
+++ b/llvm/lib/Analysis/CostModel.cpp
@@ -88,6 +88,23 @@ static bool isReverseVectorMask(SmallVector<int, 16> &Mask) {
   return true;
 }
 
+static TargetTransformInfo::OperandValueKind getOperandInfo(Value *V) {
+  TargetTransformInfo::OperandValueKind OpInfo =
+    TargetTransformInfo::OK_AnyValue;
+
+  // Check for a splat of a constant.
+  ConstantDataVector *CDV = 0;
+  if ((CDV = dyn_cast<ConstantDataVector>(V)))
+    if (CDV->getSplatValue() != NULL)
+      OpInfo = TargetTransformInfo::OK_UniformConstantValue;
+  ConstantVector *CV = 0;
+  if ((CV = dyn_cast<ConstantVector>(V)))
+    if (CV->getSplatValue() != NULL)
+      OpInfo = TargetTransformInfo::OK_UniformConstantValue;
+
+  return OpInfo;
+}
+
 unsigned CostModelAnalysis::getInstructionCost(const Instruction *I) const {
   if (!TTI)
     return -1;
@@ -121,7 +138,12 @@ unsigned CostModelAnalysis::getInstructionCost(const Instruction *I) const {
   case Instruction::And:
   case Instruction::Or:
   case Instruction::Xor: {
-    return TTI->getArithmeticInstrCost(I->getOpcode(), I->getType());
+    TargetTransformInfo::OperandValueKind Op1VK =
+      getOperandInfo(I->getOperand(0));
+    TargetTransformInfo::OperandValueKind Op2VK =
+      getOperandInfo(I->getOperand(1));
+    return TTI->getArithmeticInstrCost(I->getOpcode(), I->getType(), Op1VK,
+                                       Op2VK);
   }
   case Instruction::Select: {
     const SelectInst *SI = cast<SelectInst>(I);