[llvm-commits] [llvm] r39788 - /llvm/trunk/lib/Transforms/Scalar/FastDSE.cpp

[Owen Anderson]

Author: resistor
Date: Thu Jul 12 12:52:20 2007
New Revision: 39788

URL: http://llvm.org/viewvc/llvm-project?rev=39788&view=rev
Log:
Remove the end-block handling code.  It was unsafe, and making it safe would have resulted in falling back to the slow DSE case.  I need to think some more about the right way to handle this.

Modified:
    llvm/trunk/lib/Transforms/Scalar/FastDSE.cpp

Modified: llvm/trunk/lib/Transforms/Scalar/FastDSE.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Scalar/FastDSE.cpp?rev=39788&r1=39787&r2=39788&view=diff

==============================================================================
--- llvm/trunk/lib/Transforms/Scalar/FastDSE.cpp (original)
+++ llvm/trunk/lib/Transforms/Scalar/FastDSE.cpp Thu Jul 12 12:52:20 2007
@@ -122,11 +122,6 @@
     }
   }
   
-  // If this block ends in a return, unwind, unreachable, and eventually
-  // tailcall, then all allocas are dead at its end.
-  if (BB.getTerminator()->getNumSuccessors() == 0)
-    MadeChange |= handleEndBlock(BB, possiblyDead);
-  
   // Do a trivial DCE
   while (!possiblyDead.empty()) {
     Instruction *I = possiblyDead.back();
@@ -168,56 +163,6 @@
   return false;
 }
 
-/// handleEndBlock - Remove dead stores to stack-allocated locations in the function
-/// end block
-bool FDSE::handleEndBlock(BasicBlock& BB, SetVector<Instruction*>& possiblyDead) {
-  MemoryDependenceAnalysis &MD = getAnalysis<MemoryDependenceAnalysis>();
-  
-  bool MadeChange = false;
-  
-  // Pointers alloca'd in this function are dead in the end block
-  SmallPtrSet<AllocaInst*, 4> deadPointers;
-  
-  // Find all of the alloca'd pointers in the entry block
-  BasicBlock *Entry = BB.getParent()->begin();
-  for (BasicBlock::iterator I = Entry->begin(), E = Entry->end(); I != E; ++I)
-    if (AllocaInst *AI = dyn_cast<AllocaInst>(I))
-      deadPointers.insert(AI);
-  
-  // Scan the basic block backwards
-  for (BasicBlock::iterator BBI = BB.end(); BBI != BB.begin(); ){
-    --BBI;
-    
-    if (deadPointers.empty())
-      break;
-    
-    // If we find a store whose pointer is dead...
-    if (StoreInst* S = dyn_cast<StoreInst>(BBI)) {
-      if (deadPointers.count(S->getPointerOperand())){
-        // Remove it!
-        MD.removeInstruction(S);
-        
-        // DCE instructions only used to calculate that store
-        if (Instruction* D = dyn_cast<Instruction>(S->getOperand(0)))
-          possiblyDead.insert(D);
-        
-        BBI++;
-        S->eraseFromParent();
-        NumFastStores++;
-        MadeChange = true;
-      }
-    
-    // If we encounter a use of the pointer, it is no longer considered dead
-    } else if (LoadInst* L = dyn_cast<LoadInst>(BBI)) {
-      deadPointers.erase(L->getPointerOperand());
-    } else if (VAArgInst* V = dyn_cast<VAArgInst>(BBI)) {
-      deadPointers.erase(V->getOperand(0));
-    }
-  }
-  
-  return MadeChange;
-}
-
 void FDSE::DeleteDeadInstructionChains(Instruction *I,
                                       SetVector<Instruction*> &DeadInsts) {
   // Instruction must be dead.