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, 178 insertions, 0 deletions

diff --git a/lib/Transforms/Utils/GlobalStatus.cpp b/lib/Transforms/Utils/GlobalStatus.cpp
new file mode 100644
index 0000000000..8fb79aa87b
--- /dev/null
+++ b/lib/Transforms/Utils/GlobalStatus.cpp
@@ -0,0 +1,178 @@
+//===-- GlobalStatus.cpp - Compute status info for globals -----------------==//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/ADT/SmallPtrSet.h"
+#include "llvm/IR/BasicBlock.h"
+#include "llvm/IR/GlobalVariable.h"
+#include "llvm/IR/IntrinsicInst.h"
+#include "llvm/Transforms/Utils/GlobalStatus.h"
+
+using namespace llvm;
+
+/// Return the stronger of the two ordering. If the two orderings are acquire
+/// and release, then return AcquireRelease.
+///
+static AtomicOrdering strongerOrdering(AtomicOrdering X, AtomicOrdering Y) {
+  if (X == Acquire && Y == Release)
+    return AcquireRelease;
+  if (Y == Acquire && X == Release)
+    return AcquireRelease;
+  return (AtomicOrdering)std::max(X, Y);
+}
+
+/// 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 llvm::isSafeToDestroyConstant(const Constant *C) {
+  if (isa<GlobalValue>(C))
+    return false;
+
+  for (Value::const_use_iterator UI = C->use_begin(), E = C->use_end(); UI != E;
+       ++UI)
+    if (const Constant *CU = dyn_cast<Constant>(*UI)) {
+      if (!isSafeToDestroyConstant(CU))
+        return false;
+    } else
+      return false;
+  return true;
+}
+
+static bool analyzeGlobalAux(const Value *V, GlobalStatus &GS,
+                             SmallPtrSet<const PHINode *, 16> &PhiUsers) {
+  for (Value::const_use_iterator UI = V->use_begin(), E = V->use_end(); UI != E;
+       ++UI) {
+    const User *U = *UI;
+    if (const ConstantExpr *CE = dyn_cast<ConstantExpr>(U)) {
+      GS.HasNonInstructionUser = true;
+
+      // If the result of the constantexpr isn't pointer type, then we won't
+      // know to expect it in various places.  Just reject early.
+      if (!isa<PointerType>(CE->getType()))
+        return true;
+
+      if (analyzeGlobalAux(CE, GS, PhiUsers))
+        return true;
+    } else if (const Instruction *I = dyn_cast<Instruction>(U)) {
+      if (!GS.HasMultipleAccessingFunctions) {
+        const Function *F = I->getParent()->getParent();
+        if (GS.AccessingFunction == 0)
+          GS.AccessingFunction = F;
+        else if (GS.AccessingFunction != F)
+          GS.HasMultipleAccessingFunctions = true;
+      }
+      if (const LoadInst *LI = dyn_cast<LoadInst>(I)) {
+        GS.IsLoaded = true;
+        // Don't hack on volatile loads.
+        if (LI->isVolatile())
+          return true;
+        GS.Ordering = strongerOrdering(GS.Ordering, LI->getOrdering());
+      } else if (const StoreInst *SI = dyn_cast<StoreInst>(I)) {
+        // Don't allow a store OF the address, only stores TO the address.
+        if (SI->getOperand(0) == V)
+          return true;
+
+        // Don't hack on volatile stores.
+        if (SI->isVolatile())
+          return true;
+
+        GS.Ordering = strongerOrdering(GS.Ordering, SI->getOrdering());
+
+        // If this is a direct store to the global (i.e., the global is a scalar
+        // value, not an aggregate), keep more specific information about
+        // stores.
+        if (GS.StoredType != GlobalStatus::Stored) {
+          if (const GlobalVariable *GV =
+                  dyn_cast<GlobalVariable>(SI->getOperand(1))) {
+            Value *StoredVal = SI->getOperand(0);
+
+            if (Constant *C = dyn_cast<Constant>(StoredVal)) {
+              if (C->isThreadDependent()) {
+                // The stored value changes between threads; don't track it.
+                return true;
+              }
+            }
+
+            if (StoredVal == GV->getInitializer()) {
+              if (GS.StoredType < GlobalStatus::InitializerStored)
+                GS.StoredType = GlobalStatus::InitializerStored;
+            } else if (isa<LoadInst>(StoredVal) &&
+                       cast<LoadInst>(StoredVal)->getOperand(0) == GV) {
+              if (GS.StoredType < GlobalStatus::InitializerStored)
+                GS.StoredType = GlobalStatus::InitializerStored;
+            } else if (GS.StoredType < GlobalStatus::StoredOnce) {
+              GS.StoredType = GlobalStatus::StoredOnce;
+              GS.StoredOnceValue = StoredVal;
+            } else if (GS.StoredType == GlobalStatus::StoredOnce &&
+                       GS.StoredOnceValue == StoredVal) {
+              // noop.
+            } else {
+              GS.StoredType = GlobalStatus::Stored;
+            }
+          } else {
+            GS.StoredType = GlobalStatus::Stored;
+          }
+        }
+      } else if (isa<BitCastInst>(I)) {
+        if (analyzeGlobalAux(I, GS, PhiUsers))
+          return true;
+      } else if (isa<GetElementPtrInst>(I)) {
+        if (analyzeGlobalAux(I, GS, PhiUsers))
+          return true;
+      } else if (isa<SelectInst>(I)) {
+        if (analyzeGlobalAux(I, GS, PhiUsers))
+          return true;
+      } else if (const PHINode *PN = dyn_cast<PHINode>(I)) {
+        // PHI nodes we can check just like select or GEP instructions, but we
+        // have to be careful about infinite recursion.
+        if (PhiUsers.insert(PN)) // Not already visited.
+          if (analyzeGlobalAux(I, GS, PhiUsers))
+            return true;
+      } else if (isa<CmpInst>(I)) {
+        GS.IsCompared = true;
+      } else if (const MemTransferInst *MTI = dyn_cast<MemTransferInst>(I)) {
+        if (MTI->isVolatile())
+          return true;
+        if (MTI->getArgOperand(0) == V)
+          GS.StoredType = GlobalStatus::Stored;
+        if (MTI->getArgOperand(1) == V)
+          GS.IsLoaded = true;
+      } else if (const MemSetInst *MSI = dyn_cast<MemSetInst>(I)) {
+        assert(MSI->getArgOperand(0) == V && "Memset only takes one pointer!");
+        if (MSI->isVolatile())
+          return true;
+        GS.StoredType = GlobalStatus::Stored;
+      } else {
+        return true; // Any other non-load instruction might take address!
+      }
+    } else if (const Constant *C = dyn_cast<Constant>(U)) {
+      GS.HasNonInstructionUser = true;
+      // We might have a dead and dangling constant hanging off of here.
+      if (!isSafeToDestroyConstant(C))
+        return true;
+    } else {
+      GS.HasNonInstructionUser = true;
+      // Otherwise must be some other user.
+      return true;
+    }
+  }
+
+  return false;
+}
+
+bool GlobalStatus::analyzeGlobal(const Value *V, GlobalStatus &GS) {
+  SmallPtrSet<const PHINode *, 16> PhiUsers;
+  return analyzeGlobalAux(V, GS, PhiUsers);
+}
+
+GlobalStatus::GlobalStatus()
+    : IsCompared(false), IsLoaded(false), StoredType(NotStored),
+      StoredOnceValue(0), AccessingFunction(0),
+      HasMultipleAccessingFunctions(false), HasNonInstructionUser(false),
+      Ordering(NotAtomic) {}