Ensure NoDefinitions gets initialized only at first use.

As a global, NoDefinitions could get initialized at program startup, which happens specifically with Visual Studio. This causes the progam to abort because its initialization depends on a TLS variable to be (manually) initialized first. Since there's only one use of NoDefinitions, it can be moved to that location and since it's at function scope it only gets constructed at first use. BUG=swiftshader:7 Change-Id: I30801ad0d0ab380ead33069f174bb78dc1b230ab Reviewed-on: https://chromium-review.googlesource.com/379955Tested-by: Nicolas Capens <nicolascapens@google.com> Reviewed-by: Jim Stichnoth <stichnot@chromium.org>

Ensure NoDefinitions gets initialized only at first use.
86e5d883 · Nicolas Capens · Nicolas Capens · 0e137b2e · 86e5d883 · 86e5d883
Commit 86e5d883 authored Sep 08, 2016 by Nicolas Capens Committed by Nicolas Capens Sep 09, 2016
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Showing with 13 additions and 4 deletions

IceOperand.cpp src/IceOperand.cpp +12 -3

IceOperand.h src/IceOperand.h +1 -1

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--- a/src/IceOperand.cpp
+++ b/src/IceOperand.cpp
@@ -509,8 +509,17 @@ const Inst *VariablesMetadata::getFirstDefinition(const Variable *Var) const {
 const InstDefList &
 VariablesMetadata::getLatterDefinitions(const Variable *Var) const {
  assert(Kind == VMK_All);
-  if (!isTracked(Var))
+  if (!isTracked(Var)) {
-    return NoDefinitions;
+    // NoDefinitions has to be initialized after we've had a chance to set the
+    // CfgAllocator, so it can't be a static global object. Also, while C++11
+    // guarantees the initialization of static local objects to be thread-safe,
+    // we use a pointer to it so we can avoid frequent  mutex locking overhead.
+    if (NoDefinitions == nullptr) {
+      static const InstDefList NoDefinitionsInstance;
+      NoDefinitions = &NoDefinitionsInstance;
+    }
+    return *NoDefinitions;
+  }
  SizeT VarNum = Var->getIndex();
  return Metadata[VarNum].getLatterDefinitions();
 }
@@ -529,7 +538,7 @@ RegWeight VariablesMetadata::getUseWeight(const Variable *Var) const {
  return Metadata[VarNum].getUseWeight();
 }
-const InstDefList VariablesMetadata::NoDefinitions;
+const InstDefList *VariablesMetadata::NoDefinitions = nullptr;
 // ======================== dump routines ======================== //

--- a/src/IceOperand.h
+++ b/src/IceOperand.h
@@ -1075,7 +1075,7 @@ private:
  const Cfg *Func;
  MetadataKind Kind;
  CfgVector<VariableTracking> Metadata;
-  const static InstDefList NoDefinitions;
+  static const InstDefList *NoDefinitions;
 };
 /// BooleanVariable represents a variable that was the zero-extended result of a