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//===- llvm/Transforms/HoistPHIConstants.h - Normalize PHI nodes ------------=//
//
// HoistPHIConstants - Remove literal constants that are arguments of PHI nodes
// by inserting cast instructions in the preceeding basic blocks, and changing
// constant references into references of the casted value.
//
//===----------------------------------------------------------------------===//
#include "llvm/Transforms/HoistPHIConstants.h"
#include "llvm/iPHINode.h"
#include "llvm/iOther.h"
#include "llvm/BasicBlock.h"
#include "llvm/Function.h"
#include "llvm/Pass.h"
#include <map>
#include <vector>
typedef std::pair<BasicBlock *, Value*> BBConstTy;
typedef std::map<BBConstTy, CastInst *> CachedCopyMap;
static Value *NormalizePhiOperand(PHINode *PN, Value *CPV,
BasicBlock *Pred, CachedCopyMap &CopyCache) {
// Check if we've already inserted a copy for this constant in Pred
// Note that `copyCache[Pred]' will create an empty vector the first time
//
CachedCopyMap::iterator CCI = CopyCache.find(BBConstTy(Pred, CPV));
if (CCI != CopyCache.end()) return CCI->second;
// Create a copy instruction and add it to the cache...
CastInst *Inst = new CastInst(CPV, CPV->getType());
CopyCache.insert(std::make_pair(BBConstTy(Pred, CPV), Inst));
// Insert the copy just before the terminator inst of the predecessor BB
assert(Pred->getTerminator() && "Degenerate BB encountered!");
Pred->getInstList().insert(Pred->getInstList().end()-1, Inst);
return Inst;
}
//---------------------------------------------------------------------------
// Entry point for normalizing constant args in PHIs
//---------------------------------------------------------------------------
static bool doHoistPHIConstants(Function *M) {
CachedCopyMap Cache;
bool Changed = false;
for (Function::iterator BI = M->begin(), BE = M->end(); BI != BE; ++BI) {
std::vector<PHINode*> phis; // normalizing invalidates BB iterator
for (BasicBlock::iterator II = (*BI)->begin(); II != (*BI)->end(); ++II) {
if (PHINode *PN = dyn_cast<PHINode>(*II))
phis.push_back(PN);
else
break; // All PHIs occur at top of BB!
}
for (std::vector<PHINode*>::iterator PI=phis.begin(); PI != phis.end();++PI)
for (unsigned i = 0; i < (*PI)->getNumIncomingValues(); ++i) {
Value *Op = (*PI)->getIncomingValue(i);
if (isa<Constant>(Op)) {
(*PI)->setIncomingValue(i,
NormalizePhiOperand((*PI),
(*PI)->getIncomingValue(i),
(*PI)->getIncomingBlock(i), Cache));
Changed = true;
}
}
}
return Changed;
}
namespace {
struct HoistPHIConstants : public FunctionPass {
const char *getPassName() const { return "Hoist Constants from PHI Nodes"; }
virtual bool runOnFunction(Function *F) { return doHoistPHIConstants(F); }
virtual void getAnalysisUsage(AnalysisUsage &AU) const {
AU.preservesCFG();
}
};
}
Pass *createHoistPHIConstantsPass() { return new HoistPHIConstants(); }
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