[llvm-commits] [llvm] r120359 - /llvm/trunk/lib/Transforms/Scalar/DeadStoreElimination.cpp

[Chris Lattner]

Author: lattner
Date: Mon Nov 29 18:01:19 2010
New Revision: 120359

URL: http://llvm.org/viewvc/llvm-project?rev=120359&view=rev
Log:
two changes to DSE that shouldn't affect anything:

1. Don't bother trying to optimize:

lifetime.end(ptr)
store(ptr)

as it is undefined, and therefore shouldn't exist.

2. Move the 'storing a loaded pointer' xform up, simplifying
  the may-aliased store code.


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=120359&r1=120358&r2=120359&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/Scalar/DeadStoreElimination.cpp (original)
+++ llvm/trunk/lib/Transforms/Scalar/DeadStoreElimination.cpp Mon Nov 29 18:01:19 2010
@@ -204,10 +204,10 @@
     // If we find a store or a free, get its memory dependence.
     if (!doesClobberMemory(Inst) && !isFreeCall(Inst))
       continue;
-    
+
     MemDepResult InstDep = MD.getDependency(Inst);
     
-    // Ignore non-local stores.
+    // Ignore non-local store liveness.
     // FIXME: cross-block DSE would be fun. :)
     if (InstDep.isNonLocal()) continue;
   
@@ -216,7 +216,30 @@
       MadeChange |= handleFreeWithNonTrivialDependency(F, Inst, InstDep);
       continue;
     }
-    
+
+    // If we're storing the same value back to a pointer that we just
+    // loaded from, then the store can be removed.
+    if (StoreInst *SI = dyn_cast<StoreInst>(Inst)) {
+      if (LoadInst *DepLoad = dyn_cast<LoadInst>(InstDep.getInst())) {
+        if (SI->getPointerOperand() == DepLoad->getPointerOperand() &&
+            SI->getOperand(0) == DepLoad) {
+          // DeleteDeadInstruction can delete the current instruction.  Save BBI
+          // in case we need it.
+          WeakVH NextInst(BBI);
+          
+          DeleteDeadInstruction(SI);
+          
+          if (NextInst == 0)  // Next instruction deleted.
+            BBI = BB.begin();
+          else if (BBI != BB.begin())  // Revisit this instruction if possible.
+            --BBI;
+          ++NumFastStores;
+          MadeChange = true;
+          continue;
+        }
+      }
+    }
+     
     if (!InstDep.isDef()) {
       // If this is a may-aliased store that is clobbering the store value, we
       // can keep searching past it for another must-aliased pointer that stores
@@ -234,20 +257,13 @@
           InstDep = MD.getPointerDependencyFrom(Loc, false, InstDep.getInst(),
                                                 &BB);
       }
-        
-      // If not a definite must-alias store dependency, ignore it.  If this is a
-      // load from the same pointer, we don't want to transform load+store into
-      // a noop.
-      if (!InstDep.isDef() || !isa<StoreInst>(InstDep.getInst()))
-        continue;
     }
     
     // If this is a store-store dependence, then the previous store is dead so
     // long as this store is at least as big as it.
-    if (doesClobberMemory(InstDep.getInst())) {
+    if (InstDep.isDef() && doesClobberMemory(InstDep.getInst())) {
       Instruction *DepStore = InstDep.getInst();
-      if (isStoreAtLeastAsWideAs(Inst, DepStore, TD) &&
-          isElidable(DepStore)) {
+      if (isStoreAtLeastAsWideAs(Inst, DepStore, TD) && isElidable(DepStore)) {
         // Delete the store and now-dead instructions that feed it.
         DeleteDeadInstruction(DepStore);
         ++NumFastStores;
@@ -261,52 +277,6 @@
         continue;
       }
     }
-    
-    if (!isElidable(Inst))
-      continue;
-    
-    // If we're storing the same value back to a pointer that we just
-    // loaded from, then the store can be removed.
-    if (StoreInst *SI = dyn_cast<StoreInst>(Inst)) {
-      if (LoadInst *DepLoad = dyn_cast<LoadInst>(InstDep.getInst())) {
-        if (SI->getPointerOperand() == DepLoad->getPointerOperand() &&
-            SI->getOperand(0) == DepLoad) {
-          // DeleteDeadInstruction can delete the current instruction.  Save BBI
-          // in case we need it.
-          WeakVH NextInst(BBI);
-          
-          DeleteDeadInstruction(SI);
-          
-          if (NextInst == 0)  // Next instruction deleted.
-            BBI = BB.begin();
-          else if (BBI != BB.begin())  // Revisit this instruction if possible.
-            --BBI;
-          ++NumFastStores;
-          MadeChange = true;
-          continue;
-        }
-      }
-    }
-    
-    // If this is a lifetime end marker, we can throw away the store.
-    if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(InstDep.getInst())) {
-      if (II->getIntrinsicID() == Intrinsic::lifetime_end) {
-        // Delete the store and now-dead instructions that feed it.
-        // DeleteDeadInstruction can delete the current instruction.  Save BBI
-        // in case we need it.
-        WeakVH NextInst(BBI);
-        
-        DeleteDeadInstruction(Inst);
-        
-        if (NextInst == 0)  // Next instruction deleted.
-          BBI = BB.begin();
-        else if (BBI != BB.begin())  // Revisit this instruction if possible.
-          --BBI;
-        ++NumFastStores;
-        MadeChange = true;
-        continue;
-      }
-    }
   }
   
   // If this block ends in a return, unwind, or unreachable, all allocas are