[RDF] Fix liveness propagation through shadows

Each shadow only represents data flow that is restricted to its reaching
def. Propagating more than that could lead to spurious register liveness,
resulting in extra (incorrectly) block live-ins.

llvm-svn: 283143

1 files changed, 7 insertions, 29 deletions

diff --git a/llvm/lib/Target/Hexagon/RDFLiveness.cpp b/llvm/lib/Target/Hexagon/RDFLiveness.cpp
index efc45112518..d3b2d579e5b 100644
--- a/llvm/lib/Target/Hexagon/RDFLiveness.cpp
+++ b/llvm/lib/Target/Hexagon/RDFLiveness.cpp
@@ -530,7 +530,7 @@ void Liveness::computePhiInfo() {
         RegisterSet UpReached;
         for (const std::pair<RegisterRef,NodeSet> &T : RUM) {
           RegisterRef R = T.first;
-          if (!isRestrictedToRef(PA, UA, R))
+          if (UA.Addr->getFlags() & NodeAttrs::Shadow)
             R = getRestrictedRegRef(UA);
           if (!MidDefs.hasCoverOf(R))
             UpReached.insert(R);
@@ -648,7 +648,7 @@ void Liveness::computeLiveIns() {
         auto &LOX = PhiLOX[PrA.Addr->getCode()];
         for (auto R : RUs) {
           RegisterRef RR = R.first;
-          if (!isRestrictedToRef(PA, UA, RR))
+          if (UA.Addr->getFlags() & NodeAttrs::Shadow)
             RR = getRestrictedRegRef(UA);
           // The restricted ref may be different from the ref that was
           // accessed in the "real use". This means that this phi use
@@ -770,29 +770,6 @@ void Liveness::resetKills(MachineBasicBlock *B) {
 }
 
 
-// For shadows, determine if RR is aliased to a reaching def of any other
-// shadow associated with RA. The register ref on RA will be "larger" than
-// each individual reaching def, and to determine the data-flow between defs
-// and uses of RR it may be necessary to visit all shadows. If RR is not
-// aliased to the reaching def of any other shadow, then visiting only RA
-// is sufficient. In that sense, the data flow of RR would be restricted to
-// the reference RA.
-// For non-shadows, this function returns "true".
-bool Liveness::isRestrictedToRef(NodeAddr<InstrNode*> IA, NodeAddr<RefNode*> RA,
-      RegisterRef RR) const {
-  NodeId Start = RA.Id;
-  for (NodeAddr<RefNode*> TA = DFG.getNextShadow(IA, RA);
-       TA.Id != 0 && TA.Id != Start; TA = DFG.getNextShadow(IA, TA)) {
-    NodeId RD = TA.Addr->getReachingDef();
-    if (RD == 0)
-      continue;
-    if (DFG.alias(RR, DFG.addr<DefNode*>(RD).Addr->getRegRef()))
-      return false;
-  }
-  return true;
-}
-
-
 RegisterRef Liveness::getRestrictedRegRef(NodeAddr<RefNode*> RA) const {
   assert(DFG.IsRef<NodeAttrs::Use>(RA));
   if (RA.Addr->getFlags() & NodeAttrs::Shadow) {
@@ -850,12 +827,13 @@ void Liveness::traverse(MachineBasicBlock *B, RefMap &LiveIn) {
   }
 
   if (Trace) {
-    dbgs() << LLVM_FUNCTION_NAME << " in BB#" << B->getNumber()
-           << " after recursion into";
+    dbgs() << "\n-- BB#" << B->getNumber() << ": " << LLVM_FUNCTION_NAME
+           << " after recursion into: {";
     for (auto I : *N)
       dbgs() << ' ' << I->getBlock()->getNumber();
-    dbgs() << "\n  LiveIn: " << Print<RefMap>(LiveIn, DFG);
-    dbgs() << "\n  Local:  " << Print<RegisterSet>(LiveMap[B], DFG) << '\n';
+    dbgs() << " }\n";
+    dbgs() << "  LiveIn: " << Print<RefMap>(LiveIn, DFG) << '\n';
+    dbgs() << "  Local:  " << Print<RegisterSet>(LiveMap[B], DFG) << '\n';
   }
 
   // Add phi uses that are live on exit from this block.