#include "llvm/ADT/SmallPtrSet.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/Analysis/AliasAnalysis.h"
+#include "llvm/Analysis/Dominators.h"
#include "llvm/Analysis/MemoryDependenceAnalysis.h"
#include "llvm/Target/TargetData.h"
#include "llvm/Transforms/Utils/Local.h"
// Dependence Graph)
virtual void getAnalysisUsage(AnalysisUsage &AU) const {
AU.setPreservesCFG();
+ AU.addRequired<DominatorTree>();
AU.addRequired<TargetData>();
AU.addRequired<AliasAnalysis>();
AU.addRequired<MemoryDependenceAnalysis>();
+ AU.addPreserved<DominatorTree>();
AU.addPreserved<AliasAnalysis>();
AU.addPreserved<MemoryDependenceAnalysis>();
}
// No known stores after the free
last = 0;
} else {
- // Update our most-recent-store map.
- last = cast<StoreInst>(BBI);
+ StoreInst* S = cast<StoreInst>(BBI);
+
+ // If we're storing the same value back to a pointer that we just
+ // loaded from, then the store can be removed;
+ if (LoadInst* L = dyn_cast<LoadInst>(S->getOperand(0))) {
+ Instruction* dep = MD.getDependency(S);
+ DominatorTree& DT = getAnalysis<DominatorTree>();
+
+ if (S->getParent() == L->getParent() &&
+ S->getPointerOperand() == L->getPointerOperand() &&
+ ( dep == MemoryDependenceAnalysis::None ||
+ dep == MemoryDependenceAnalysis::NonLocal ||
+ DT.dominates(dep, L))) {
+ if (Instruction* D = dyn_cast<Instruction>(S->getOperand(0)))
+ possiblyDead.insert(D);
+ if (Instruction* D = dyn_cast<Instruction>(S->getOperand(1)))
+ possiblyDead.insert(D);
+
+ // Avoid iterator invalidation.
+ BBI--;
+
+ MD.removeInstruction(S);
+ S->eraseFromParent();
+ NumFastStores++;
+ MadeChange = true;
+ } else
+ // Update our most-recent-store map.
+ last = S;
+ } else
+ // Update our most-recent-store map.
+ last = S;
}
}
possiblyDead.insert(D);
BBI++;
+ MD.removeInstruction(S);
S->eraseFromParent();
NumFastStores++;
MadeChange = true;