Transform @llvm.objectsize to integer if the argument is a result of malloc of known size.

llvm-svn: 97860

1 files changed, 10 insertions, 0 deletions

diff --git a/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp b/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
index a241f169f28..85c3895b2a0 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
@@ -336,6 +336,16 @@ Instruction *InstCombiner::visitCallInst(CallInst &CI) {
         }
         return ReplaceInstUsesWith(CI, ConstantInt::get(ReturnTy, AllocaSize));
       }
+    } else if (CallInst *MI = extractMallocCall(Op1)) {
+      const Type* MallocType = getMallocAllocatedType(MI);
+      // Get alloca size.
+      if (MallocType->isSized()) {
+        if (Value *NElems = getMallocArraySize(MI, TD, true)) {
+          if (ConstantInt *NElements = dyn_cast<ConstantInt>(NElems))
+        return ReplaceInstUsesWith(CI, ConstantInt::get(ReturnTy,
+               (NElements->getZExtValue() * TD->getTypeAllocSize(MallocType))));
+        }
+      }
     } else if (ConstantExpr *CE = dyn_cast<ConstantExpr>(Op1)) {      
       // Only handle constant GEPs here.
       if (CE->getOpcode() != Instruction::GetElementPtr) break;