Don't build switch lookup tables for dllimport or TLS variables

We would previously put dllimport variables in switch lookup tables, which
doesn't work because the address cannot be used in a constant initializer.
This is basically the same problem that we have in PR19955.

Putting TLS variables in switch tables also desn't work, because the
address of such a variable is not constant.

Differential Revision: http://reviews.llvm.org/D4220

llvm-svn: 211331

2 files changed, 37 insertions, 20 deletions

diff --git a/llvm/lib/IR/Constants.cpp b/llvm/lib/IR/Constants.cpp
index aa26cff6a7b..5851625383b 100644
--- a/llvm/lib/IR/Constants.cpp
+++ b/llvm/lib/IR/Constants.cpp
@@ -278,35 +278,48 @@ bool Constant::canTrap() const {
   return canTrapImpl(this, NonTrappingOps);
 }
 
-/// isThreadDependent - Return true if the value can vary between threads.
-bool Constant::isThreadDependent() const {
-  SmallPtrSet<const Constant*, 64> Visited;
-  SmallVector<const Constant*, 64> WorkList;
-  WorkList.push_back(this);
-  Visited.insert(this);
+/// Check if C contains a GlobalValue for which Predicate is true.
+static bool
+ConstHasGlobalValuePredicate(const Constant *C,
+                             bool (*Predicate)(const GlobalValue *)) {
+  SmallPtrSet<const Constant *, 8> Visited;
+  SmallVector<const Constant *, 8> WorkList;
+  WorkList.push_back(C);
+  Visited.insert(C);
 
   while (!WorkList.empty()) {
-    const Constant *C = WorkList.pop_back_val();
-
-    if (const GlobalVariable *GV = dyn_cast<GlobalVariable>(C)) {
-      if (GV->isThreadLocal())
+    const Constant *WorkItem = WorkList.pop_back_val();
+    if (const auto *GV = dyn_cast<GlobalValue>(WorkItem))
+      if (Predicate(GV))
         return true;
-    }
-
-    for (unsigned I = 0, E = C->getNumOperands(); I != E; ++I) {
-      const Constant *D = dyn_cast<Constant>(C->getOperand(I));
-      if (!D)
+    for (const Value *Op : WorkItem->operands()) {
+      const Constant *ConstOp = dyn_cast<Constant>(Op);
+      if (!ConstOp)
         continue;
-      if (Visited.insert(D))
-        WorkList.push_back(D);
+      if (Visited.insert(ConstOp))
+        WorkList.push_back(ConstOp);
     }
   }
-
   return false;
 }
 
-/// isConstantUsed - Return true if the constant has users other than constant
-/// exprs and other dangling things.
+/// Return true if the value can vary between threads.
+bool Constant::isThreadDependent() const {
+  auto DLLImportPredicate = [](const GlobalValue *GV) {
+    return GV->isThreadLocal();
+  };
+  return ConstHasGlobalValuePredicate(this, DLLImportPredicate);
+}
+
+bool Constant::isDLLImportDependent() const {
+  auto DLLImportPredicate = [](const GlobalValue *GV) {
+    return GV->hasDLLImportStorageClass();
+  };
+  return ConstHasGlobalValuePredicate(this, DLLImportPredicate);
+}
+
+/// Return true if the constant has users other than constant exprs and other
+/// dangling things.
 bool Constant::isConstantUsed() const {
   for (const User *U : users()) {
     const Constant *UC = dyn_cast<Constant>(U);
diff --git a/llvm/lib/Transforms/Utils/SimplifyCFG.cpp b/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
index e155daf6fcc..ff2f2a03622 100644
--- a/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
+++ b/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
@@ -3313,6 +3313,10 @@ static bool ForwardSwitchConditionToPHI(SwitchInst *SI) {
 static bool ValidLookupTableConstant(Constant *C) {
   if (ConstantExpr *CE = dyn_cast<ConstantExpr>(C))
     return CE->isGEPWithNoNotionalOverIndexing();
+  if (C->isThreadDependent())
+    return false;
+  if (C->isDLLImportDependent())
+    return false;
 
   return isa<ConstantFP>(C) ||
       isa<ConstantInt>(C) ||