Allow call-slop optzn for destinations with a suitable dereferenceable attribute

[oota-llvm.git] / lib / Transforms / Scalar / MemCpyOptimizer.cpp

diff --git a/lib/Transforms/Scalar/MemCpyOptimizer.cpp b/lib/Transforms/Scalar/MemCpyOptimizer.cpp
index 9709dfcc1f685a4804a41261d43d62b923278554..be524be0082af01c6aae8c492f8f5b0065f84f05 100644 (file)
--- a/lib/Transforms/Scalar/MemCpyOptimizer.cpp
+++ b/lib/Transforms/Scalar/MemCpyOptimizer.cpp
@@ -634,22 +634,24 @@ bool MemCpyOpt::performCallSlotOptzn(Instruction *cpy,
     if (destSize < srcSize)
       return false;
   } else if (Argument *A = dyn_cast<Argument>(cpyDest)) {
-    // If the destination is an sret parameter then only accesses that are
-    // outside of the returned struct type can trap.
-    if (!A->hasStructRetAttr())
-      return false;
+    if (A->getDereferenceableBytes() < srcSize) {
+      // If the destination is an sret parameter then only accesses that are
+      // outside of the returned struct type can trap.
+      if (!A->hasStructRetAttr())
+        return false;
 
-    Type *StructTy = cast<PointerType>(A->getType())->getElementType();
-    if (!StructTy->isSized()) {
-      // The call may never return and hence the copy-instruction may never
-      // be executed, and therefore it's not safe to say "the destination
-      // has at least <cpyLen> bytes, as implied by the copy-instruction",
-      return false;
-    }
+      Type *StructTy = cast<PointerType>(A->getType())->getElementType();
+      if (!StructTy->isSized()) {
+        // The call may never return and hence the copy-instruction may never
+        // be executed, and therefore it's not safe to say "the destination
+        // has at least <cpyLen> bytes, as implied by the copy-instruction",
+        return false;
+      }
 
-    uint64_t destSize = DL->getTypeAllocSize(StructTy);
-    if (destSize < srcSize)
-      return false;
+      uint64_t destSize = DL->getTypeAllocSize(StructTy);
+      if (destSize < srcSize)
+        return false;
+    }
   } else {
     return false;
   }