Remove AllocSpill/FreeSpill

Doesn't work, so we shouldn't maintain it.  We can add a
feature like this later if we need it (although it might be easier and
just as good to just increase the preallocated spill number if
needed).

hphp/doc/ir.specification

@@ -1258,15 +1258,6 @@ D:T = Reload S0:T
 
   Loads from a spilled temporary S0, and stores the result in D.
 
-AllocSpill S0:ConstInt
-
-  Allocates S0 slots of additional spill space on the stack.
-  Generated when the preallocated spill space is exhausted.
-
-FreeSpill S0:ConstInt
-
-  Deallocates S0 slots of spill space on the stack.
-
 
 16. Continuations & Closures
 

hphp/runtime/vm/translator/hopt/codegen.cpp

@@ -2352,28 +2352,6 @@ void CodeGenerator::cgFreeActRec(IRInstruction* inst) {
              m_regs[inst->getDst()].getReg());
 }
 
-void CodeGenerator::cgAllocSpill(IRInstruction* inst) {
-  SSATmp* numSlots = inst->getSrc(0);
-
-  assert(numSlots->isConst());
-  int64_t n = numSlots->getValInt();
-  assert(n >= 0 && n % 2 == 0);
-  if (n > 0) {
-    m_as.sub_imm32_reg64(spillSlotsToSize(n), reg::rsp);
-  }
-}
-
-void CodeGenerator::cgFreeSpill(IRInstruction* inst) {
-  SSATmp* numSlots = inst->getSrc(0);
-
-  assert(numSlots->isConst());
-  int64_t n = numSlots->getValInt();
-  assert(n >= 0 && n % 2 == 0);
-  if (n > 0) {
-    m_as.add_imm32_reg64(spillSlotsToSize(n), reg::rsp);
-  }
-}
-
 void CodeGenerator::cgSpill(IRInstruction* inst) {
   SSATmp* dst   = inst->getDst();
   SSATmp* src   = inst->getSrc(0);

hphp/runtime/vm/translator/hopt/ir.h

@@ -416,8 +416,6 @@ O(InterpOneCF,                      ND, S(FramePtr) S(StkPtr)                 \
                                           C(Int),          T|E|N|Mem|Refs|Er) \
 O(Spill,                       DofS(0), SUnk,                            Mem) \
 O(Reload,                      DofS(0), SUnk,                            Mem) \
-O(AllocSpill,                       ND, C(Int),                        E|Mem) \
-O(FreeSpill,                        ND, C(Int),                        E|Mem) \
 O(CreateCont,                   D(Obj), C(TCA)                                \
                                           S(FramePtr)                         \
                                           C(Bool)                             \

hphp/runtime/vm/translator/hopt/linearscan.cpp

@@ -146,8 +146,6 @@ private:
   static SSATmp* getSpilledTmp(SSATmp* tmp);
   static SSATmp* getOrigTmp(SSATmp* tmp);
   uint32_t assignSpillLoc();
-  void insertAllocFreeSpill(Trace* trace, uint32_t numExtraSpillLocs);
-  void insertAllocFreeSpillAux(Trace* trace, uint32_t numExtraSpillLocs);
   void rematerialize();
   void rematerializeAux();
   void removeUnusedSpills();
@@ -573,47 +571,6 @@ uint32_t LinearScan::assignSpillLoc() {
   return maxSpillLoc;
 }
 
-void LinearScan::insertAllocFreeSpill(Trace* trace,
-                                      uint32_t numExtraSpillLocs) {
-  insertAllocFreeSpillAux(trace, numExtraSpillLocs);
-  for (Trace* exit : trace->getExitTraces()) {
-    insertAllocFreeSpillAux(exit, numExtraSpillLocs);
-  }
-}
-
-void LinearScan::insertAllocFreeSpillAux(Trace* trace,
-                                         uint32_t numExtraSpillLocs) {
-  SSATmp* tmp = m_irFactory->gen(DefConst, Type::Int,
-    ConstData(numExtraSpillLocs))->getDst();
-
-  for (Block* block : trace->getBlocks()) {
-    for (auto it = block->begin(); it != block->end(); ) {
-      auto next = it; ++next;
-      IRInstruction& inst = *it;
-      Opcode opc = inst.op();
-      if (opc == Call) {
-        // Insert FreeSpill and AllocSpill around each Call.
-        IRInstruction* allocSpill = m_irFactory->gen(AllocSpill, tmp);
-        IRInstruction* freeSpill = m_irFactory->gen(FreeSpill, tmp);
-        block->insert(it, freeSpill);
-        block->insert(next, allocSpill);
-      } else if (opc == ExitTrace || opc == ExitSlow || opc == ExitTraceCc ||
-                 opc == ExitSlowNoProgress || opc == ExitGuardFailure ||
-                 opc == LdRetAddr) {
-        // Insert FreeSpill at trace exits.
-        IRInstruction* freeSpill = m_irFactory->gen(FreeSpill, tmp);
-        block->insert(it, freeSpill);
-      }
-      it = next;
-    }
-  }
-
-  // Insert AllocSpill at the start of the main trace.
-  if (trace->isMain()) {
-    trace->front()->prepend(m_irFactory->gen(AllocSpill, tmp));
-  }
-}
-
 void LinearScan::collectInfo(BlockList::iterator it, Trace* trace) {
   m_natives.clear();
   m_jmps.reset();
@@ -967,18 +924,7 @@ RegAllocInfo LinearScan::allocRegs(Trace* trace, LifetimeInfo* lifetime) {
     ++numSpillLocs;
   }
   if (numSpillLocs > (uint32_t)NumPreAllocatedSpillLocs) {
-    /*
-     * We only insert AllocSpill and FreeSpill when the pre-allocated
-     * spill locations are not enough.
-     *
-     * AllocSpill and FreeSpill take the number of extra spill locations
-     * besides the pre-allocated ones.
-     *
-     * TODO(#2044051) AllocSpill/FreeSpill are currently disabled
-     * due to bugs.
-     */
-    PUNT(LinearScan_AllocSpill);
-    insertAllocFreeSpill(trace, numSpillLocs - NumPreAllocatedSpillLocs);
+    PUNT(LinearScan_TooManySpills);
   }
 
   if (m_slots.size()) genSpillStats(trace, numSpillLocs);

hphp/runtime/vm/translator/hopt/linearscan.h

@@ -195,12 +195,8 @@ RegAllocInfo allocRegsForTrace(Trace*, IRFactory*, LifetimeInfo* = nullptr);
 // +---------------+
 // |  return addr  |
 // +---------------+
-// |    extra      |  <-- spill[2]
-// |    spill      |  <-- spill[1]
-// |  locations    |  <-- spill[0]
-// +---------------+  <-- %rsp
-// If a spill location falls into the pre-allocated region, we
-// need to increase its index by 1 to avoid overwriting the
+//
+// We need to increase spill indexes by 1 to avoid overwriting the
 // return address.
 
 /*