Teach gcroot how to handle dynamically realigned frames

I'm playing with supporting custom stack map formats with statepoints.  While 
doing so, I noticed that the existing implementation didn't indicate inherently 
unsized frames.  This change essentially just ports the functionality that already 
exists for the default StackMaps section to custom stackmaps.

llvm-svn: 233891

1 files changed, 10 insertions, 7 deletions

diff --git a/llvm/lib/CodeGen/GCRootLowering.cpp b/llvm/lib/CodeGen/GCRootLowering.cpp
index 9d38e4cad13..ac351656a4a 100644
--- a/llvm/lib/CodeGen/GCRootLowering.cpp
+++ b/llvm/lib/CodeGen/GCRootLowering.cpp
@@ -332,19 +332,22 @@ bool GCMachineCodeAnalysis::runOnMachineFunction(MachineFunction &MF) {
     return false;
 
   FI = &getAnalysis<GCModuleInfo>().getFunctionInfo(*MF.getFunction());
-  if (!FI->getStrategy().needsSafePoints())
-    return false;
-
   MMI = &getAnalysis<MachineModuleInfo>();
   TII = MF.getSubtarget().getInstrInfo();
 
-  // Find the size of the stack frame.
-  FI->setFrameSize(MF.getFrameInfo()->getStackSize());
+  // Find the size of the stack frame.  There may be no correct static frame
+  // size, we use UINT64_MAX to represent this.
+  const MachineFrameInfo *MFI = MF.getFrameInfo();
+  const TargetRegisterInfo *RegInfo = MF.getSubtarget().getRegisterInfo();
+  const bool DynamicFrameSize = MFI->hasVarSizedObjects() ||
+    RegInfo->needsStackRealignment(MF);
+  FI->setFrameSize(DynamicFrameSize ? UINT64_MAX : MFI->getStackSize());
 
   // Find all safe points.
-  FindSafePoints(MF);
+  if (FI->getStrategy().needsSafePoints())
+    FindSafePoints(MF);
 
-  // Find the stack offsets for all roots.
+  // Find the concrete stack offsets for all roots (stack slots)
   FindStackOffsets(MF);
 
   return false;