Use the same spill slot for all live ranges that descend form the same original

register.

This avoids some silly stack slot shuffling when both sides of a copy get
spilled.

llvm-svn: 126353

1 files changed, 13 insertions, 4 deletions

diff --git a/llvm/lib/CodeGen/InlineSpiller.cpp b/llvm/lib/CodeGen/InlineSpiller.cpp
index ba37e544e7d..38e6c859026 100644
--- a/llvm/lib/CodeGen/InlineSpiller.cpp
+++ b/llvm/lib/CodeGen/InlineSpiller.cpp
@@ -345,7 +345,8 @@ void InlineSpiller::spill(LiveRangeEdit &edit) {
          && "Trying to spill a stack slot.");
   DEBUG(dbgs() << "Inline spilling "
                << mri_.getRegClass(edit.getReg())->getName()
-               << ':' << edit.getParent() << "\n");
+               << ':' << edit.getParent() << "\nFrom original "
+               << PrintReg(vrm_.getOriginal(edit.getReg())) << '\n');
   assert(edit.getParent().isSpillable() &&
          "Attempting to spill already spilled value.");
 
@@ -356,12 +357,20 @@ void InlineSpiller::spill(LiveRangeEdit &edit) {
     return;
 
   rc_ = mri_.getRegClass(edit.getReg());
-  stackSlot_ = vrm_.assignVirt2StackSlot(edit_->getReg());
+
+  // Share a stack slot among all descendants of Orig.
+  unsigned Orig = vrm_.getOriginal(edit.getReg());
+  stackSlot_ = vrm_.getStackSlot(Orig);
+  if (stackSlot_ == VirtRegMap::NO_STACK_SLOT)
+    stackSlot_ = vrm_.assignVirt2StackSlot(Orig);
+
+  if (Orig != edit.getReg())
+    vrm_.assignVirt2StackSlot(edit.getReg(), stackSlot_);
 
   // Update LiveStacks now that we are committed to spilling.
   LiveInterval &stacklvr = lss_.getOrCreateInterval(stackSlot_, rc_);
-  assert(stacklvr.empty() && "Just created stack slot not empty");
-  stacklvr.getNextValue(SlotIndex(), 0, lss_.getVNInfoAllocator());
+  if (!stacklvr.hasAtLeastOneValue())
+    stacklvr.getNextValue(SlotIndex(), 0, lss_.getVNInfoAllocator());
   stacklvr.MergeRangesInAsValue(edit_->getParent(), stacklvr.getValNumInfo(0));
 
   // Iterate over instructions using register.