1 files changed, 20 insertions, 0 deletions
diff --git a/lib/Transforms/Scalar/GVN.cpp b/lib/Transforms/Scalar/GVN.cpp
index 6d07ddd..106eba0 100644
--- a/lib/Transforms/Scalar/GVN.cpp
+++ b/lib/Transforms/Scalar/GVN.cpp
@@ -1464,6 +1464,13 @@ void GVN::AnalyzeLoadAvailability(LoadInst *LI, LoadDepVect &Deps,
       continue;
     }
 
+    // Loading from calloc (which zero initializes memory) -> zero
+    if (isCallocLikeFn(DepInst, TLI)) {
+      ValuesPerBlock.push_back(AvailableValueInBlock::get(
+          DepBB, Constant::getNullValue(LI->getType())));
+      continue;
+    }
+
     if (StoreInst *S = dyn_cast<StoreInst>(DepInst)) {
       // Reject loads and stores that are to the same address but are of
       // different types if we have to.
@@ -1791,6 +1798,10 @@ static void patchReplacementInstruction(Instruction *I, Value *Repl) {
       case LLVMContext::MD_fpmath:
         ReplInst->setMetadata(Kind, MDNode::getMostGenericFPMath(IMD, ReplMD));
         break;
+      case LLVMContext::MD_invariant_load:
+        // Only set the !invariant.load if it is present in both instructions.
+        ReplInst->setMetadata(Kind, IMD);
+        break;
       }
     }
   }
@@ -1988,6 +1999,15 @@ bool GVN::processLoad(LoadInst *L) {
     }
   }
 
+  // If this load follows a calloc (which zero initializes memory),
+  // then the loaded value is zero
+  if (isCallocLikeFn(DepInst, TLI)) {
+    L->replaceAllUsesWith(Constant::getNullValue(L->getType()));
+    markInstructionForDeletion(L);
+    ++NumGVNLoad;
+    return true;
+  }
+
   return false;
 }