Subzero: Remove Variable::NeedsStackSlot.

src/IceTargetLoweringX8632.cpp

 //===- subzero/src/IceTargetLoweringX8632.cpp - x86-32 lowering -----------===//
 //
 //                        The Subzero Code Generator
 //
 // This file is distributed under the University of Illinois Open Source
 // License. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
 //
 // This file implements the TargetLoweringX8632 class, which
@@ skipping 259 matching lines @@
                 "Inconsistency between ICETYPEX8632_TABLE and ICETYPE_TABLE");
 ICETYPE_TABLE;
 #undef X
 } // end of namespace dummy3
 
 } // end of anonymous namespace
 
 TargetX8632::TargetX8632(Cfg *Func)
     : TargetLowering(Func), InstructionSet(CLInstructionSet),
       IsEbpBasedFrame(false), NeedsStackAlignment(false), FrameSizeLocals(0),
-      SpillAreaSizeBytes(0), NextLabelNumber(0), ComputedLiveRanges(false) {
+      SpillAreaSizeBytes(0), NextLabelNumber(0) {
   // TODO: Don't initialize IntegerRegisters and friends every time.
   // Instead, initialize in some sort of static initializer for the
   // class.
   llvm::SmallBitVector IntegerRegisters(RegX8632::Reg_NUM);
   llvm::SmallBitVector IntegerRegistersI8(RegX8632::Reg_NUM);
   llvm::SmallBitVector FloatRegisters(RegX8632::Reg_NUM);
   llvm::SmallBitVector VectorRegisters(RegX8632::Reg_NUM);
   llvm::SmallBitVector InvalidRegisters(RegX8632::Reg_NUM);
   ScratchRegs.resize(RegX8632::Reg_NUM);
 #define X(val, encode, name, name16, name8, scratch, preserved, stackptr,      \
@@ skipping 75 matching lines @@
   // full liveness analysis.
   Func->renumberInstructions();
   if (Func->hasError())
     return;
   Func->liveness(Liveness_Intervals);
   if (Func->hasError())
     return;
   // Validate the live range computations.  The expensive validation
   // call is deliberately only made when assertions are enabled.
   assert(Func->validateLiveness());
-  ComputedLiveRanges = true;
   // The post-codegen dump is done here, after liveness analysis and
   // associated cleanup, to make the dump cleaner and more useful.
   Func->dump("After initial x8632 codegen");
   Func->getVMetadata()->init(VMK_All);
   regAlloc();
   if (Func->hasError())
     return;
   Func->dump("After linear scan regalloc");
 
   if (Ctx->getFlags().PhiEdgeSplit) {
@@ skipping 273 matching lines @@
   //
   // The following variables record the size in bytes of the given areas:
   //  * X86_RET_IP_SIZE_BYTES:  area 1
   //  * PreservedRegsSizeBytes: area 2
   //  * SpillAreaPaddingBytes:  area 3
   //  * GlobalsSize:            area 4
   //  * GlobalsAndSubsequentPaddingSize: areas 4 - 5
   //  * LocalsSpillAreaSize:    area 6
   //  * SpillAreaSizeBytes:     areas 3 - 7
 
+  // Make a final pass over the Cfg to determine which variables need
+  // stack slots.
+  llvm::BitVector NeedsStackSlot(Func->getNumVariables());
+  for (CfgNode *Node : Func->getNodes()) {
+    for (auto Inst = Node->getInsts().begin(), E = Node->getInsts().end();
+         Inst != E; ++Inst) {
+      if (Inst->isDeleted())
+        continue;

[jvoung (off chromium), 2014/11/11 17:18:09]

If the instruction isRedundantAssign() should this be skipped too?

[Jim Stichnoth, 2014/11/11 17:43:38]

No, isRedundantAssign() depends on the frame offsets being assigned, and at this
point that hasn't happened yet.

+      if (const Variable *Var = Inst->getDest())
+        NeedsStackSlot[Var->getIndex()] = true;

[jvoung (off chromium), 2014/11/11 17:18:10]

should this check if (!Var->hasReg()) first?

[Jim Stichnoth, 2014/11/11 17:43:39]

Good point.  It turns out that neither hasReg() check is actually necessary,
because the check is repeated (in line 741 of this version of the file).

I removed the check here, and renamed NeedsStackSlot to IsVarReferenced to
capture a more general meaning.

+      for (SizeT I = 0; I < Inst->getSrcSize(); ++I) {
+        Operand *Src = Inst->getSrc(I);
+        SizeT NumVars = Src->getNumVars();
+        for (SizeT J = 0; J < NumVars; ++J) {
+          const Variable *Var = Src->getVar(J);
+          if (!Var->hasReg())
+            NeedsStackSlot[Var->getIndex()] = true;
+        }
+      }
+    }
+  }
+
   // If SimpleCoalescing is false, each variable without a register
   // gets its own unique stack slot, which leads to large stack
   // frames.  If SimpleCoalescing is true, then each "global" variable
   // without a register gets its own slot, but "local" variable slots
   // are reused across basic blocks.  E.g., if A and B are local to
   // block 1 and C is local to block 2, then C may share a slot with A or B.
   //
   // We cannot coalesce stack slots if this function calls a "returns twice"
   // function. In that case, basic blocks may be revisited, and variables
   // local to those basic blocks are actually live until after the
@@ skipping 39 matching lines @@
   for (Variable *Var : Variables) {
     if (Var->hasReg()) {
       RegsUsed[Var->getRegNum()] = true;
       continue;
     }
     // An argument either does not need a stack slot (if passed in a
     // register) or already has one (if passed on the stack).
     if (Var->getIsArg())
       continue;
     // An unreferenced variable doesn't need a stack slot.
-    if (ComputedLiveRanges && !Var->needsStackSlot())
+    if (!NeedsStackSlot[Var->getIndex()])
       continue;
     // A spill slot linked to a variable with a stack slot should reuse
     // that stack slot.
     if (SpillVariable *SpillVar = llvm::dyn_cast<SpillVariable>(Var)) {
       assert(Var->getWeight() == RegWeight::Zero);
       if (!SpillVar->getLinkedTo()->hasReg()) {
         VariablesLinkedToSpillSlots.push_back(Var);
         continue;
       }
     }
@@ skipping 3507 matching lines @@
       // TODO(stichnot): Opportunity for register randomization.
       int32_t RegNum = AvailRegsForType.find_first();
       bool IsVector = isVectorType(Dest->getType());
       bool NeedSpill = (RegNum == -1);
       if (NeedSpill) {
         // Pick some register to spill and update RegNum.
         // TODO(stichnot): Opportunity for register randomization.
         RegNum = RegsForType.find_first();
         Preg = getPhysicalRegister(RegNum, Dest->getType());
         SpillLoc = Func->makeVariable(Dest->getType());
-        SpillLoc->setNeedsStackSlot();
         if (IsVector)
           _movp(SpillLoc, Preg);
         else
           _mov(SpillLoc, Preg);
       }
       assert(RegNum >= 0);
       if (llvm::isa<ConstantUndef>(Src))
         // Materialize an actual constant instead of undef.  RegNum is
         // passed in for vector types because undef vectors are
         // lowered to vector register of zeroes.
@@ skipping 456 matching lines @@
   } else if (IsConstant || IsExternal)
     Str << "\t.zero\t" << Size << "\n";
   // Size is part of .comm.
 
   if (IsConstant || HasNonzeroInitializer || IsExternal)
     Str << "\t.size\t" << MangledName << ", " << Size << "\n";
   // Size is part of .comm.
 }
 
 } // end of namespace Ice