Revert "[VirtRegRewriter] Avoid clobbering registers when expanding copy bundles"

There's an msan failure:

  http://lab.llvm.org:8011/builders/sanitizer-x86_64-linux-fast/builds/19549

This reverts r334750.

llvm-svn: 334754

Author: bogner

llvm/lib/CodeGen/VirtRegMap.cpp

@@ -406,62 +406,23 @@ void VirtRegRewriter::expandCopyBundle(MachineInstr &MI) const {
     return;
 
   if (MI.isBundledWithPred() && !MI.isBundledWithSucc()) {
-    SmallVector<MachineInstr *, 2> MIs({&MI});
-
     // Only do this when the complete bundle is made out of COPYs.
     MachineBasicBlock &MBB = *MI.getParent();
     for (MachineBasicBlock::reverse_instr_iterator I =
          std::next(MI.getReverseIterator()), E = MBB.instr_rend();
          I != E && I->isBundledWithSucc(); ++I) {
       if (!I->isCopy())
         return;
-      MIs.push_back(&*I);
-    }
-    MachineInstr *FirstMI = MIs.back();
-
-    auto anyRegsAlias = [](const MachineInstr *Dst,
-                           ArrayRef<MachineInstr *> Srcs,
-                           const TargetRegisterInfo *TRI) {
-      for (const MachineInstr *Src : Srcs)
-        if (Src != Dst)
-          if (TRI->regsOverlap(Dst->getOperand(0).getReg(),
-                               Src->getOperand(1).getReg()))
-            return true;
-      return false;
-    };
-
-    // If any of the destination registers in the bundle of copies alias any of
-    // the source registers, try to schedule the instructions to avoid any
-    // clobbering.
-    for (int E = MIs.size(), PrevE; E > 1; PrevE = E) {
-      for (int I = E; I--; )
-        if (!anyRegsAlias(MIs[I], makeArrayRef(MIs).take_front(E), TRI)) {
-          if (I + 1 != E)
-            std::swap(MIs[I], MIs[E - 1]);
-          --E;
-        }
-      if (PrevE == E) {
-        MF->getFunction().getContext().emitError(
-            "register rewriting failed: cycle in copy bundle");
-        break;
-      }
     }
 
-    MachineInstr *BundleStart = FirstMI;
-    for (MachineInstr *BundledMI : llvm::reverse(MIs)) {
-      // If instruction is in the middle of the bundle, move it before the
-      // bundle starts, otherwise, just unbundle it. When we get to the last
-      // instruction, the bundle will have been completely undone.
-      if (BundledMI != BundleStart) {
-        BundledMI->removeFromBundle();
-        MBB.insert(FirstMI, BundledMI);
-      } else if (BundledMI->isBundledWithSucc()) {
-        BundledMI->unbundleFromSucc();
-        BundleStart = &*std::next(BundledMI->getIterator());
-      }
+    for (MachineBasicBlock::reverse_instr_iterator I = MI.getReverseIterator();
+         I->isBundledWithPred(); ) {
+      MachineInstr &MI = *I;
+      ++I;
 
-      if (Indexes && BundledMI != FirstMI)
-        Indexes->insertMachineInstrInMaps(*BundledMI);
+      MI.unbundleFromPred();
+      if (Indexes)
+        Indexes->insertMachineInstrInMaps(MI);
     }
   }
 }