llvm-6502/lib/Analysis/CostModel.cpp
Arnold Schwaighofer 6bf4f67641 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

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@178807 91177308-0d34-0410-b5e6-96231b3b80d8
2013-04-04 23:26:21 +00:00

248 lines
8.2 KiB
C++

//===- CostModel.cpp ------ Cost Model Analysis ---------------------------===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file defines the cost model analysis. It provides a very basic cost
// estimation for LLVM-IR. This analysis uses the services of the codegen
// to approximate the cost of any IR instruction when lowered to machine
// instructions. The cost results are unit-less and the cost number represents
// the throughput of the machine assuming that all loads hit the cache, all
// branches are predicted, etc. The cost numbers can be added in order to
// compare two or more transformation alternatives.
//
//===----------------------------------------------------------------------===//
#define CM_NAME "cost-model"
#define DEBUG_TYPE CM_NAME
#include "llvm/Analysis/Passes.h"
#include "llvm/Analysis/TargetTransformInfo.h"
#include "llvm/IR/Function.h"
#include "llvm/IR/Instructions.h"
#include "llvm/IR/IntrinsicInst.h"
#include "llvm/IR/Value.h"
#include "llvm/Pass.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/raw_ostream.h"
using namespace llvm;
namespace {
class CostModelAnalysis : public FunctionPass {
public:
static char ID; // Class identification, replacement for typeinfo
CostModelAnalysis() : FunctionPass(ID), F(0), TTI(0) {
initializeCostModelAnalysisPass(
*PassRegistry::getPassRegistry());
}
/// Returns the expected cost of the instruction.
/// Returns -1 if the cost is unknown.
/// Note, this method does not cache the cost calculation and it
/// can be expensive in some cases.
unsigned getInstructionCost(const Instruction *I) const;
private:
virtual void getAnalysisUsage(AnalysisUsage &AU) const;
virtual bool runOnFunction(Function &F);
virtual void print(raw_ostream &OS, const Module*) const;
/// The function that we analyze.
Function *F;
/// Target information.
const TargetTransformInfo *TTI;
};
} // End of anonymous namespace
// Register this pass.
char CostModelAnalysis::ID = 0;
static const char cm_name[] = "Cost Model Analysis";
INITIALIZE_PASS_BEGIN(CostModelAnalysis, CM_NAME, cm_name, false, true)
INITIALIZE_PASS_END (CostModelAnalysis, CM_NAME, cm_name, false, true)
FunctionPass *llvm::createCostModelAnalysisPass() {
return new CostModelAnalysis();
}
void
CostModelAnalysis::getAnalysisUsage(AnalysisUsage &AU) const {
AU.setPreservesAll();
}
bool
CostModelAnalysis::runOnFunction(Function &F) {
this->F = &F;
TTI = getAnalysisIfAvailable<TargetTransformInfo>();
return false;
}
static bool isReverseVectorMask(SmallVector<int, 16> &Mask) {
for (unsigned i = 0, MaskSize = Mask.size(); i < MaskSize; ++i)
if (Mask[i] > 0 && Mask[i] != (int)(MaskSize - 1 - i))
return false;
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;
switch (I->getOpcode()) {
case Instruction::GetElementPtr:{
Type *ValTy = I->getOperand(0)->getType()->getPointerElementType();
return TTI->getAddressComputationCost(ValTy);
}
case Instruction::Ret:
case Instruction::PHI:
case Instruction::Br: {
return TTI->getCFInstrCost(I->getOpcode());
}
case Instruction::Add:
case Instruction::FAdd:
case Instruction::Sub:
case Instruction::FSub:
case Instruction::Mul:
case Instruction::FMul:
case Instruction::UDiv:
case Instruction::SDiv:
case Instruction::FDiv:
case Instruction::URem:
case Instruction::SRem:
case Instruction::FRem:
case Instruction::Shl:
case Instruction::LShr:
case Instruction::AShr:
case Instruction::And:
case Instruction::Or:
case Instruction::Xor: {
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);
Type *CondTy = SI->getCondition()->getType();
return TTI->getCmpSelInstrCost(I->getOpcode(), I->getType(), CondTy);
}
case Instruction::ICmp:
case Instruction::FCmp: {
Type *ValTy = I->getOperand(0)->getType();
return TTI->getCmpSelInstrCost(I->getOpcode(), ValTy);
}
case Instruction::Store: {
const StoreInst *SI = cast<StoreInst>(I);
Type *ValTy = SI->getValueOperand()->getType();
return TTI->getMemoryOpCost(I->getOpcode(), ValTy,
SI->getAlignment(),
SI->getPointerAddressSpace());
}
case Instruction::Load: {
const LoadInst *LI = cast<LoadInst>(I);
return TTI->getMemoryOpCost(I->getOpcode(), I->getType(),
LI->getAlignment(),
LI->getPointerAddressSpace());
}
case Instruction::ZExt:
case Instruction::SExt:
case Instruction::FPToUI:
case Instruction::FPToSI:
case Instruction::FPExt:
case Instruction::PtrToInt:
case Instruction::IntToPtr:
case Instruction::SIToFP:
case Instruction::UIToFP:
case Instruction::Trunc:
case Instruction::FPTrunc:
case Instruction::BitCast: {
Type *SrcTy = I->getOperand(0)->getType();
return TTI->getCastInstrCost(I->getOpcode(), I->getType(), SrcTy);
}
case Instruction::ExtractElement: {
const ExtractElementInst * EEI = cast<ExtractElementInst>(I);
ConstantInt *CI = dyn_cast<ConstantInt>(I->getOperand(1));
unsigned Idx = -1;
if (CI)
Idx = CI->getZExtValue();
return TTI->getVectorInstrCost(I->getOpcode(),
EEI->getOperand(0)->getType(), Idx);
}
case Instruction::InsertElement: {
const InsertElementInst * IE = cast<InsertElementInst>(I);
ConstantInt *CI = dyn_cast<ConstantInt>(IE->getOperand(2));
unsigned Idx = -1;
if (CI)
Idx = CI->getZExtValue();
return TTI->getVectorInstrCost(I->getOpcode(),
IE->getType(), Idx);
}
case Instruction::ShuffleVector: {
const ShuffleVectorInst *Shuffle = cast<ShuffleVectorInst>(I);
Type *VecTypOp0 = Shuffle->getOperand(0)->getType();
unsigned NumVecElems = VecTypOp0->getVectorNumElements();
SmallVector<int, 16> Mask = Shuffle->getShuffleMask();
if (NumVecElems == Mask.size() && isReverseVectorMask(Mask))
return TTI->getShuffleCost(TargetTransformInfo::SK_Reverse, VecTypOp0, 0,
0);
return -1;
}
case Instruction::Call:
if (const IntrinsicInst *II = dyn_cast<IntrinsicInst>(I)) {
SmallVector<Type*, 4> Tys;
for (unsigned J = 0, JE = II->getNumArgOperands(); J != JE; ++J)
Tys.push_back(II->getArgOperand(J)->getType());
return TTI->getIntrinsicInstrCost(II->getIntrinsicID(), II->getType(),
Tys);
}
return -1;
default:
// We don't have any information on this instruction.
return -1;
}
}
void CostModelAnalysis::print(raw_ostream &OS, const Module*) const {
if (!F)
return;
for (Function::iterator B = F->begin(), BE = F->end(); B != BE; ++B) {
for (BasicBlock::iterator it = B->begin(), e = B->end(); it != e; ++it) {
Instruction *Inst = it;
unsigned Cost = getInstructionCost(Inst);
if (Cost != (unsigned)-1)
OS << "Cost Model: Found an estimated cost of " << Cost;
else
OS << "Cost Model: Unknown cost";
OS << " for instruction: "<< *Inst << "\n";
}
}
}