Remove GC roots that reference dead objects.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@166763 91177308-0d34-0410-b5e6-96231b3b80d8

2 files changed, 15 insertions, 3 deletions

diff --git a/include/llvm/CodeGen/GCMetadata.h b/include/llvm/CodeGen/GCMetadata.h
index 20e33f74f6..076f6f39fe 100644
--- a/include/llvm/CodeGen/GCMetadata.h
+++ b/include/llvm/CodeGen/GCMetadata.h
@@ -122,6 +122,11 @@ namespace llvm {
       Roots.push_back(GCRoot(Num, Metadata));
     }
 
+    /// removeStackRoot - Removes a root.
+    roots_iterator removeStackRoot(roots_iterator position) {
+      return Roots.erase(position);
+    }
+
     /// addSafePoint - Notes the existence of a safe point. Num is the ID of the
     /// label just prior to the safe point (if the code generator is using
     /// MachineModuleInfo).
diff --git a/lib/CodeGen/GCStrategy.cpp b/lib/CodeGen/GCStrategy.cpp
index 8de541de3d..f4755bb163 100644
--- a/lib/CodeGen/GCStrategy.cpp
+++ b/lib/CodeGen/GCStrategy.cpp
@@ -388,9 +388,16 @@ void GCMachineCodeAnalysis::FindStackOffsets(MachineFunction &MF) {
   const TargetFrameLowering *TFI = TM->getFrameLowering();
   assert(TFI && "TargetRegisterInfo not available!");
 
-  for (GCFunctionInfo::roots_iterator RI = FI->roots_begin(),
-                                      RE = FI->roots_end(); RI != RE; ++RI)
-    RI->StackOffset = TFI->getFrameIndexOffset(MF, RI->Num);
+  for (GCFunctionInfo::roots_iterator RI = FI->roots_begin();
+       RI != FI->roots_end();) {
+    // If the root references a dead object, no need to keep it.
+    if (MF.getFrameInfo()->isDeadObjectIndex(RI->Num)) {
+      RI = FI->removeStackRoot(RI);
+    } else {
+      RI->StackOffset = TFI->getFrameIndexOffset(MF, RI->Num);
+      ++RI;
+    }
+  }
 }
 
 bool GCMachineCodeAnalysis::runOnMachineFunction(MachineFunction &MF) {