PNaCl: Fix nacl-expand-ctors pass to handle llvm.global_ctors being zeroinitializer

This case can happen if optimisation removes initializers.

BUG=http://code.google.com/p/nativeclient/issues/detail?id=3018
TEST=test/Transforms/NaCl/expand-ctors-zeroinit.ll

Review URL: https://codereview.chromium.org/11190028

2 files changed, 34 insertions, 16 deletions

diff --git a/lib/Transforms/NaCl/ExpandCtors.cpp b/lib/Transforms/NaCl/ExpandCtors.cpp
index 9c5f2cd2d7..6b8130e4fb 100644
--- a/lib/Transforms/NaCl/ExpandCtors.cpp
+++ b/lib/Transforms/NaCl/ExpandCtors.cpp
@@ -79,22 +79,24 @@ static void defineFuncArray(Module &M, const char *LlvmArrayName,
   std::vector<Constant*> Funcs;
 
   GlobalVariable *Array = M.getNamedGlobal(LlvmArrayName);
-  if (Array && Array->hasInitializer()) {
-    ConstantArray *InitList = cast<ConstantArray>(Array->getInitializer());
-    std::vector<FuncArrayEntry> FuncsToSort;
-    for (unsigned Index = 0; Index < InitList->getNumOperands(); ++Index) {
-      ConstantStruct *CS = cast<ConstantStruct>(InitList->getOperand(Index));
-      FuncArrayEntry Entry;
-      Entry.priority = cast<ConstantInt>(CS->getOperand(0))->getZExtValue();
-      Entry.func = CS->getOperand(1);
-      FuncsToSort.push_back(Entry);
-    }
-
-    std::sort(FuncsToSort.begin(), FuncsToSort.end(), compareEntries);
-    for (std::vector<FuncArrayEntry>::iterator Iter = FuncsToSort.begin();
-         Iter != FuncsToSort.end();
-         ++Iter) {
-      Funcs.push_back(Iter->func);
+  if (Array) {
+    if (Array->hasInitializer() && !Array->getInitializer()->isNullValue()) {
+      ConstantArray *InitList = cast<ConstantArray>(Array->getInitializer());
+      std::vector<FuncArrayEntry> FuncsToSort;
+      for (unsigned Index = 0; Index < InitList->getNumOperands(); ++Index) {
+        ConstantStruct *CS = cast<ConstantStruct>(InitList->getOperand(Index));
+        FuncArrayEntry Entry;
+        Entry.priority = cast<ConstantInt>(CS->getOperand(0))->getZExtValue();
+        Entry.func = CS->getOperand(1);
+        FuncsToSort.push_back(Entry);
+      }
+
+      std::sort(FuncsToSort.begin(), FuncsToSort.end(), compareEntries);
+      for (std::vector<FuncArrayEntry>::iterator Iter = FuncsToSort.begin();
+           Iter != FuncsToSort.end();
+           ++Iter) {
+        Funcs.push_back(Iter->func);
+      }
     }
     // No code should be referencing global_ctors/global_dtors,
     // because this symbol is internal to LLVM.
diff --git a/test/Transforms/NaCl/expand-ctors-zeroinit.ll b/test/Transforms/NaCl/expand-ctors-zeroinit.ll
new file mode 100644
index 0000000000..d02741f0b5
--- /dev/null
+++ b/test/Transforms/NaCl/expand-ctors-zeroinit.ll
@@ -0,0 +1,16 @@
+; Currently we do not define __{init,fini}_array_end as named aliases.
+; RUN: opt < %s -nacl-expand-ctors -S | not grep __init_array_end
+; RUN: opt < %s -nacl-expand-ctors -S | not grep __fini_array_end
+
+; We expect this symbol to be removed:
+; RUN: opt < %s -nacl-expand-ctors -S | not grep llvm.global_ctors
+
+; RUN: opt < %s -nacl-expand-ctors -S | FileCheck %s
+
+; If llvm.global_ctors is zeroinitializer, it should be treated the
+; same as an empty array.
+
+@llvm.global_ctors = appending global [0 x { i32, void ()* }] zeroinitializer
+
+; CHECK: @__init_array_start = internal constant [0 x void ()*] zeroinitializer
+; CHECK: @__fini_array_start = internal constant [0 x void ()*] zeroinitializer