Optimize more linkonce_odr values during LTO.

When a linkonce_odr value that is on the dso list is not unnamed_addr
we can still look to see if anything is actually using its address. If
not, it is safe to hide it.

This patch implements that by moving GlobalStatus to Transforms/Utils
and using it in Internalize.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@193090 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 82 insertions, 0 deletions

diff --git a/include/llvm/Transforms/Utils/GlobalStatus.h b/include/llvm/Transforms/Utils/GlobalStatus.h
new file mode 100644
index 0000000000..c366095088
--- /dev/null
+++ b/include/llvm/Transforms/Utils/GlobalStatus.h
@@ -0,0 +1,82 @@
+//===- GlobalStatus.h - Compute status info for globals ---------*- C++ -*-===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_TRANSFORMS_UTILS_GLOBALSTATUS_H
+#define LLVM_TRANSFORMS_UTILS_GLOBALSTATUS_H
+
+#include "llvm/IR/Instructions.h"
+
+namespace llvm {
+class Value;
+class Function;
+
+/// It is safe to destroy a constant iff it is only used by constants itself.
+/// Note that constants cannot be cyclic, so this test is pretty easy to
+/// implement recursively.
+///
+bool isSafeToDestroyConstant(const Constant *C);
+
+/// As we analyze each global, keep track of some information about it.  If we
+/// find out that the address of the global is taken, none of this info will be
+/// accurate.
+struct GlobalStatus {
+  /// True if the global's address is used in a comparison.
+  bool IsCompared;
+
+  /// True if the global is ever loaded.  If the global isn't ever loaded it
+  /// can be deleted.
+  bool IsLoaded;
+
+  /// Keep track of what stores to the global look like.
+  enum StoredType {
+    /// There is no store to this global.  It can thus be marked constant.
+    NotStored,
+
+    /// This global is stored to, but the only thing stored is the constant it
+    /// was initialized with. This is only tracked for scalar globals.
+    InitializerStored,
+
+    /// This global is stored to, but only its initializer and one other value
+    /// is ever stored to it.  If this global isStoredOnce, we track the value
+    /// stored to it in StoredOnceValue below.  This is only tracked for scalar
+    /// globals.
+    StoredOnce,
+
+    /// This global is stored to by multiple values or something else that we
+    /// cannot track.
+    Stored
+  } StoredType;
+
+  /// If only one value (besides the initializer constant) is ever stored to
+  /// this global, keep track of what value it is.
+  Value *StoredOnceValue;
+
+  /// These start out null/false.  When the first accessing function is noticed,
+  /// it is recorded. When a second different accessing function is noticed,
+  /// HasMultipleAccessingFunctions is set to true.
+  const Function *AccessingFunction;
+  bool HasMultipleAccessingFunctions;
+
+  /// Set to true if this global has a user that is not an instruction (e.g. a
+  /// constant expr or GV initializer).
+  bool HasNonInstructionUser;
+
+  /// Set to the strongest atomic ordering requirement.
+  AtomicOrdering Ordering;
+
+  /// Look at all uses of the global and fill in the GlobalStatus structure.  If
+  /// the global has its address taken, return true to indicate we can't do
+  /// anything with it.
+  static bool analyzeGlobal(const Value *V, GlobalStatus &GS);
+
+  GlobalStatus();
+};
+}
+
+#endif