Subzero: Improve usability of liveness-related tools.

src/IceTargetLowering.cpp

 //===- subzero/src/IceTargetLowering.cpp - Basic lowering implementation --===//
 //
 //                        The Subzero Code Generator
 //
 // This file is distributed under the University of Illinois Open Source
 // License. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
 ///
 /// \file
@@ skipping 228 matching lines @@
   RegSetMask RegExclude = RegSet_None;
   RegInclude |= RegSet_CallerSave;
   RegInclude |= RegSet_CalleeSave;
   if (hasFramePointer())
     RegExclude |= RegSet_FramePointer;
   LinearScan.init(Kind);
   llvm::SmallBitVector RegMask = getRegisterSet(RegInclude, RegExclude);
   LinearScan.scan(RegMask, Ctx->getFlags().shouldRandomizeRegAlloc());
 }
 
-void TargetLowering::inferTwoAddress() {
-  // Find two-address non-SSA instructions where Dest==Src0, and set the
-  // DestNonKillable flag to keep liveness analysis consistent.
+void TargetLowering::markRedefinitions() {
+  // Find (non-SSA) instructions where the Dest variable appears in some source
+  // operand, and set the IsDestRedefined flag to keep liveness analysis
+  // consistent.
   for (auto Inst = Context.getCur(), E = Context.getNext(); Inst != E; ++Inst) {
     if (Inst->isDeleted())
       continue;
-    if (Variable *Dest = Inst->getDest()) {
-      // TODO(stichnot): We may need to consider all source operands, not just
-      // the first one, if using 3-address instructions.
-      if (Inst->getSrcSize() > 0 && Inst->getSrc(0) == Dest)
-        Inst->setDestNonKillable();
+    Variable *Dest = Inst->getDest();
+    if (Dest == nullptr)
+      continue;
+    FOREACH_VAR_IN_INST(Var, *Inst) {
+      if (Var == Dest) {
+        Inst->setDestRedefined();
+        break;
+      }
     }
   }
 }
 
 void TargetLowering::sortVarsByAlignment(VarList &Dest,
                                          const VarList &Source) const {
   Dest = Source;
   // Instead of std::sort, we could do a bucket sort with log2(alignment) as
   // the buckets, if performance is an issue.
   std::sort(Dest.begin(), Dest.end(),
@@ skipping 320 matching lines @@
   if (Target == Target_##X)                                                    \
     return TargetHeader##X::create(Ctx);
 #include "llvm/Config/SZTargets.def"
 
   llvm::report_fatal_error("Unsupported target header lowering");
 }
 
 TargetHeaderLowering::~TargetHeaderLowering() = default;
 
 } // end of namespace Ice