Treat lifetime begin/end markers as allocations/frees respectively for the

purposes for GVN/DSE.

llvm-svn: 85383

2 files changed, 41 insertions, 0 deletions

diff --git a/llvm/lib/Transforms/Scalar/DeadStoreElimination.cpp b/llvm/lib/Transforms/Scalar/DeadStoreElimination.cpp
index e3f43372ec1..60b12fd8679 100644
--- a/llvm/lib/Transforms/Scalar/DeadStoreElimination.cpp
+++ b/llvm/lib/Transforms/Scalar/DeadStoreElimination.cpp
@@ -154,6 +154,26 @@ bool DSE::runOnBasicBlock(BasicBlock &BB) {
         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(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 block ends in a return, unwind, or unreachable, all allocas are
diff --git a/llvm/lib/Transforms/Scalar/GVN.cpp b/llvm/lib/Transforms/Scalar/GVN.cpp
index 32d027aa36d..dd8859b5e84 100644
--- a/llvm/lib/Transforms/Scalar/GVN.cpp
+++ b/llvm/lib/Transforms/Scalar/GVN.cpp
@@ -1248,6 +1248,15 @@ bool GVN::processNonLocalLoad(LoadInst *LI,
                                              UndefValue::get(LI->getType())));
       continue;
     }
+    
+    // Loading immediately after lifetime begin or end -> undef.
+    if (IntrinsicInst* II = dyn_cast<IntrinsicInst>(DepInst)) {
+      if (II->getIntrinsicID() == Intrinsic::lifetime_start ||
+          II->getIntrinsicID() == Intrinsic::lifetime_end) {
+        ValuesPerBlock.push_back(AvailableValueInBlock::get(DepBB,
+                                             UndefValue::get(LI->getType())));
+      }
+    }
 
     if (StoreInst *S = dyn_cast<StoreInst>(DepInst)) {
       // Reject loads and stores that are to the same address but are of
@@ -1591,6 +1600,18 @@ bool GVN::processLoad(LoadInst *L, SmallVectorImpl<Instruction*> &toErase) {
     NumGVNLoad++;
     return true;
   }
+  
+  // If this load occurs either right after a lifetime begin or a lifetime end,
+  // then the loaded value is undefined.
+  if (IntrinsicInst* II = dyn_cast<IntrinsicInst>(DepInst)) {
+    if (II->getIntrinsicID() == Intrinsic::lifetime_start ||
+        II->getIntrinsicID() == Intrinsic::lifetime_end) {
+      L->replaceAllUsesWith(UndefValue::get(L->getType()));
+      toErase.push_back(L);
+      NumGVNLoad++;
+      return true;
+    }
+  }
 
   return false;
 }