[llvm-commits] [llvm] r120463 - /llvm/trunk/lib/Transforms/Scalar/DeadStoreElimination.cpp

[Chris Lattner]

Author: lattner
Date: Tue Nov 30 15:18:46 2010
New Revision: 120463

URL: http://llvm.org/viewvc/llvm-project?rev=120463&view=rev
Log:
move call handling in handleEndBlock up a bit, and simplify it.
If the call might read all the allocas, stop scanning early.
Convert a vector to smallvector, shrink SmallPtrSet to 16 instead
of 64 to avoid crazy linear scans.

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

Modified: llvm/trunk/lib/Transforms/Scalar/DeadStoreElimination.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Scalar/DeadStoreElimination.cpp?rev=120463&r1=120462&r2=120463&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/Scalar/DeadStoreElimination.cpp (original)
+++ llvm/trunk/lib/Transforms/Scalar/DeadStoreElimination.cpp Tue Nov 30 15:18:46 2010
@@ -66,9 +66,9 @@
     bool handleEndBlock(BasicBlock &BB);
     bool RemoveUndeadPointers(Value *Ptr, uint64_t killPointerSize,
                               BasicBlock::iterator &BBI,
-                              SmallPtrSet<Value*, 64> &deadPointers);
+                              SmallPtrSet<Value*, 16> &deadPointers);
     void DeleteDeadInstruction(Instruction *I,
-                               SmallPtrSet<Value*, 64> *deadPointers = 0);
+                               SmallPtrSet<Value*, 16> *deadPointers = 0);
     
 
     // getAnalysisUsage - We require post dominance frontiers (aka Control
@@ -400,7 +400,7 @@
   bool MadeChange = false;
   
   // Pointers alloca'd in this function are dead in the end block
-  SmallPtrSet<Value*, 64> DeadPointers;
+  SmallPtrSet<Value*, 16> DeadPointers;
   
   // Find all of the alloca'd pointers in the entry block.
   BasicBlock *Entry = BB.getParent()->begin();
@@ -450,42 +450,26 @@
       continue;
     }
     
-    
-    Value *KillPointer = 0;
-    uint64_t KillPointerSize = AliasAnalysis::UnknownSize;
-    
-    // If we encounter a use of the pointer, it is no longer considered dead
-    if (LoadInst *L = dyn_cast<LoadInst>(BBI)) {
-      KillPointer = L->getPointerOperand();
-    } else if (VAArgInst *V = dyn_cast<VAArgInst>(BBI)) {
-      KillPointer = V->getOperand(0);
-    } else if (MemTransferInst *MTI = dyn_cast<MemTransferInst>(BBI)) {
-      KillPointer = cast<MemTransferInst>(BBI)->getSource();
-      if (ConstantInt *Len = dyn_cast<ConstantInt>(MTI->getLength()))
-        KillPointerSize = Len->getZExtValue();
-    } else if (CallSite CS = cast<Value>(BBI)) {
+    if (CallSite CS = cast<Value>(BBI)) {
       // If this call does not access memory, it can't be loading any of our
       // pointers.
       if (AA->doesNotAccessMemory(CS))
         continue;
       
-      unsigned NumModRef = 0;
-      unsigned NumOther = 0;
+      unsigned NumModRef = 0, NumOther = 0;
       
-      // Remove any pointers made undead by the call from the dead set
-      std::vector<Value*> dead;
-      for (SmallPtrSet<Value*, 64>::iterator I = DeadPointers.begin(),
+      // If the call might load from any of our allocas, then any store above
+      // the call is live.
+      SmallVector<Value*, 8> LiveAllocas;
+      for (SmallPtrSet<Value*, 16>::iterator I = DeadPointers.begin(),
            E = DeadPointers.end(); I != E; ++I) {
-        // HACK: if we detect that our AA is imprecise, it's not
-        // worth it to scan the rest of the deadPointers set.  Just
-        // assume that the AA will return ModRef for everything, and
-        // go ahead and bail.
-        if (NumModRef >= 16 && NumOther == 0) {
-          DeadPointers.clear();
+        // If we detect that our AA is imprecise, it's not worth it to scan the
+        // rest of the DeadPointers set.  Just assume that the AA will return
+        // ModRef for everything, and go ahead and bail out.
+        if (NumModRef >= 16 && NumOther == 0)
           return MadeChange;
-        }
-        
-        // See if the call site touches it
+
+        // See if the call site touches it.
         AliasAnalysis::ModRefResult A = 
           AA->getModRefInfo(CS, *I, getPointerSize(*I, *AA));
         
@@ -495,14 +479,33 @@
           ++NumOther;
         
         if (A == AliasAnalysis::ModRef || A == AliasAnalysis::Ref)
-          dead.push_back(*I);
+          LiveAllocas.push_back(*I);
       }
-
-      for (std::vector<Value*>::iterator I = dead.begin(), E = dead.end();
-           I != E; ++I)
+      
+      for (SmallVector<Value*, 8>::iterator I = LiveAllocas.begin(),
+           E = LiveAllocas.end(); I != E; ++I)
         DeadPointers.erase(*I);
       
+      // If all of the allocas were clobbered by the call then we're not going
+      // to find anything else to process.
+      if (DeadPointers.empty())
+        return MadeChange;
+      
       continue;
+    }
+    
+    Value *KillPointer = 0;
+    uint64_t KillPointerSize = AliasAnalysis::UnknownSize;
+    
+    // If we encounter a use of the pointer, it is no longer considered dead
+    if (LoadInst *L = dyn_cast<LoadInst>(BBI)) {
+      KillPointer = L->getPointerOperand();
+    } else if (VAArgInst *V = dyn_cast<VAArgInst>(BBI)) {
+      KillPointer = V->getOperand(0);
+    } else if (MemTransferInst *MTI = dyn_cast<MemTransferInst>(BBI)) {
+      KillPointer = cast<MemTransferInst>(BBI)->getSource();
+      if (ConstantInt *Len = dyn_cast<ConstantInt>(MTI->getLength()))
+        KillPointerSize = Len->getZExtValue();
     } else {
       // Not a loading instruction.
       continue;
@@ -522,7 +525,7 @@
 /// undead when scanning for dead stores to alloca's.
 bool DSE::RemoveUndeadPointers(Value *killPointer, uint64_t killPointerSize,
                                BasicBlock::iterator &BBI,
-                               SmallPtrSet<Value*, 64> &DeadPointers) {
+                               SmallPtrSet<Value*, 16> &DeadPointers) {
   // If the kill pointer can be easily reduced to an alloca,
   // don't bother doing extraneous AA queries.
   if (DeadPointers.count(killPointer)) {
@@ -575,7 +578,7 @@
 /// If ValueSet is non-null, remove any deleted instructions from it as well.
 ///
 void DSE::DeleteDeadInstruction(Instruction *I,
-                                SmallPtrSet<Value*, 64> *ValueSet) {
+                                SmallPtrSet<Value*, 16> *ValueSet) {
   SmallVector<Instruction*, 32> NowDeadInsts;
   
   NowDeadInsts.push_back(I);