SplitKit: Correctly implement partial subregister copies

- This fixes a bug where subregister incompatible with the vregs register
  class where used.
- Implement the case where multiple copies are necessary to cover a
  given lanemask.

Differential Revision: https://reviews.llvm.org/D30438

llvm-svn: 298025

1 files changed, 31 insertions, 0 deletions

diff --git a/llvm/lib/CodeGen/VirtRegMap.cpp b/llvm/lib/CodeGen/VirtRegMap.cpp
index b561c6aba18..06a97fd6d4d 100644
--- a/llvm/lib/CodeGen/VirtRegMap.cpp
+++ b/llvm/lib/CodeGen/VirtRegMap.cpp
@@ -167,6 +167,7 @@ class VirtRegRewriter : public MachineFunctionPass {
   bool readsUndefSubreg(const MachineOperand &MO) const;
   void addLiveInsForSubRanges(const LiveInterval &LI, unsigned PhysReg) const;
   void handleIdentityCopy(MachineInstr &MI) const;
+  void expandCopyBundle(MachineInstr &MI) const;
 
 public:
   static char ID;
@@ -372,6 +373,34 @@ void VirtRegRewriter::handleIdentityCopy(MachineInstr &MI) const {
   DEBUG(dbgs() << "  deleted.\n");
 }
 
+/// The liverange splitting logic sometimes produces bundles of copies when
+/// subregisters are involved. Expand these into a sequence of copy instructions
+/// after processing the last in the bundle. Does not update LiveIntervals
+/// which we shouldn't need for this instruction anymore.
+void VirtRegRewriter::expandCopyBundle(MachineInstr &MI) const {
+  if (!MI.isCopy())
+    return;
+
+  if (MI.isBundledWithPred() && !MI.isBundledWithSucc()) {
+    // Only do this when the complete bundle is made out of COPYs.
+    for (MachineBasicBlock::reverse_instr_iterator I =
+         std::next(MI.getReverseIterator()); I->isBundledWithSucc(); ++I) {
+      if (!I->isCopy())
+        return;
+    }
+
+    for (MachineBasicBlock::reverse_instr_iterator I = MI.getReverseIterator();
+         I->isBundledWithPred(); ) {
+      MachineInstr &MI = *I;
+      ++I;
+
+      MI.unbundleFromPred();
+      if (Indexes)
+        Indexes->insertMachineInstrInMaps(MI);
+    }
+  }
+}
+
 void VirtRegRewriter::rewrite() {
   bool NoSubRegLiveness = !MRI->subRegLivenessEnabled();
   SmallVector<unsigned, 8> SuperDeads;
@@ -463,6 +492,8 @@ void VirtRegRewriter::rewrite() {
 
       DEBUG(dbgs() << "> " << *MI);
 
+      expandCopyBundle(*MI);
+
       // We can remove identity copies right now.
       handleIdentityCopy(*MI);
     }