Revert "LiveRegUnits: Add accumulateBackward() function"

This seems to be breaking some bots.

This reverts commit r292543.

llvm-svn: 292574

1 files changed, 32 insertions, 18 deletions

diff --git a/llvm/lib/Target/AArch64/AArch64A57FPLoadBalancing.cpp b/llvm/lib/Target/AArch64/AArch64A57FPLoadBalancing.cpp
index a589719e9b7..0aa597bcdc5 100644
--- a/llvm/lib/Target/AArch64/AArch64A57FPLoadBalancing.cpp
+++ b/llvm/lib/Target/AArch64/AArch64A57FPLoadBalancing.cpp
@@ -493,29 +493,43 @@ bool AArch64A57FPLoadBalancing::colorChainSet(std::vector<Chain*> GV,
 
 int AArch64A57FPLoadBalancing::scavengeRegister(Chain *G, Color C,
                                                 MachineBasicBlock &MBB) {
+  RegScavenger RS;
+  RS.enterBasicBlock(MBB);
+  RS.forward(MachineBasicBlock::iterator(G->getStart()));
+
   // Can we find an appropriate register that is available throughout the life
-  // of the chain? Simulate liveness backwards until the end of the chain.
-  LiveRegUnits Units(*TRI);
-  Units.addLiveOuts(MBB);
-  MachineBasicBlock::iterator I = MBB.end(), ChainEnd = G->end();
-  do {
-    --I;
-    Units.stepBackward(*I);
-  } while (I != ChainEnd);
-
-  // Check which register units are alive throughout the chain.
-  MachineBasicBlock::iterator ChainBegin = G->begin();
-  assert(ChainBegin != ChainEnd && "Chain should contain instructions");
-  do {
-    --I;
-    Units.accumulateBackward(*I);
-  } while (I != ChainBegin);
+  // of the chain?
+  unsigned RegClassID = G->getStart()->getDesc().OpInfo[0].RegClass;
+  BitVector AvailableRegs = RS.getRegsAvailable(TRI->getRegClass(RegClassID));
+  for (MachineBasicBlock::iterator I = G->begin(), E = G->end(); I != E; ++I) {
+    RS.forward(I);
+    AvailableRegs &= RS.getRegsAvailable(TRI->getRegClass(RegClassID));
+
+    // Remove any registers clobbered by a regmask or any def register that is
+    // immediately dead.
+    for (auto J : I->operands()) {
+      if (J.isRegMask())
+        AvailableRegs.clearBitsNotInMask(J.getRegMask());
+
+      if (J.isReg() && J.isDef()) {
+        MCRegAliasIterator AI(J.getReg(), TRI, /*IncludeSelf=*/true);
+        if (J.isDead())
+          for (; AI.isValid(); ++AI)
+            AvailableRegs.reset(*AI);
+#ifndef NDEBUG
+        else
+          for (; AI.isValid(); ++AI)
+            assert(!AvailableRegs[*AI] &&
+                   "Non-dead def should have been removed by now!");
+#endif
+      }
+    }
+  }
 
   // Make sure we allocate in-order, to get the cheapest registers first.
-  unsigned RegClassID = ChainBegin->getDesc().OpInfo[0].RegClass;
   auto Ord = RCI.getOrder(TRI->getRegClass(RegClassID));
   for (auto Reg : Ord) {
-    if (!Units.available(Reg))
+    if (!AvailableRegs[Reg])
       continue;
     if (C == getColor(Reg))
       return Reg;