Don't return a std::vector in the Spiller interface, but take a reference to a

vector instead. This avoids needless copying and allocation.

Add documentation.

llvm-svn: 106788

lib/CodeGen/RegAllocLinearScan.cpp

@@ -1206,8 +1206,7 @@ void RALinScan::assignRegOrStackSlotAtInterval(LiveInterval* cur) {
     DEBUG(dbgs() << "\t\t\tspilling(c): " << *cur << '\n');
     SmallVector<LiveInterval*, 8> spillIs;
     std::vector<LiveInterval*> added;
-    
-    added = spiller_->spill(cur, spillIs); 
+    spiller_->spill(cur, added, spillIs);
 
     std::sort(added.begin(), added.end(), LISorter());
     addStackInterval(cur, ls_, li_, mri_, *vrm_);
@@ -1285,10 +1284,8 @@ void RALinScan::assignRegOrStackSlotAtInterval(LiveInterval* cur) {
     if (sli->beginIndex() < earliestStart)
       earliestStart = sli->beginIndex();
        
-    std::vector<LiveInterval*> newIs;
-    newIs = spiller_->spill(sli, spillIs, &earliestStart);
+    spiller_->spill(sli, added, spillIs, &earliestStart);
     addStackInterval(sli, ls_, li_, mri_, *vrm_);
-    std::copy(newIs.begin(), newIs.end(), std::back_inserter(added));
     spilled.insert(sli->reg);
   }
 

lib/CodeGen/Spiller.cpp

@@ -67,7 +67,8 @@ protected:
   /// Add spill ranges for every use/def of the live interval, inserting loads
   /// immediately before each use, and stores after each def. No folding or
   /// remat is attempted.
-  std::vector<LiveInterval*> trivialSpillEverywhere(LiveInterval *li) {
+  void trivialSpillEverywhere(LiveInterval *li,
+                              std::vector<LiveInterval*> &newIntervals) {
     DEBUG(dbgs() << "Spilling everywhere " << *li << "\n");
 
     assert(li->weight != HUGE_VALF &&
@@ -78,8 +79,6 @@ protected:
 
     DEBUG(dbgs() << "Trivial spill everywhere of reg" << li->reg << "\n");
 
-    std::vector<LiveInterval*> added;
-    
     const TargetRegisterClass *trc = mri->getRegClass(li->reg);
     unsigned ss = vrm->assignVirt2StackSlot(li->reg);
 
@@ -157,10 +156,8 @@ protected:
         newLI->addRange(LiveRange(beginIndex, storeIndex, storeVNI));
       }
 
-      added.push_back(newLI);
+      newIntervals.push_back(newLI);
     }
-
-    return added;
   }
 };
 
@@ -176,11 +173,12 @@ public:
   TrivialSpiller(MachineFunction *mf, LiveIntervals *lis, VirtRegMap *vrm)
     : SpillerBase(mf, lis, vrm) {}
 
-  std::vector<LiveInterval*> spill(LiveInterval *li,
-                                   SmallVectorImpl<LiveInterval*> &spillIs,
-                                   SlotIndex*) {
+  void spill(LiveInterval *li,
+             std::vector<LiveInterval*> &newIntervals,
+             SmallVectorImpl<LiveInterval*> &,
+             SlotIndex*) {
     // Ignore spillIs - we don't use it.
-    return trivialSpillEverywhere(li);
+    trivialSpillEverywhere(li, newIntervals);
   }
 };
 
@@ -200,10 +198,13 @@ public:
     : lis(lis), loopInfo(loopInfo), vrm(vrm) {}
 
   /// Falls back on LiveIntervals::addIntervalsForSpills.
-  std::vector<LiveInterval*> spill(LiveInterval *li,
-                                   SmallVectorImpl<LiveInterval*> &spillIs,
-                                   SlotIndex*) {
-    return lis->addIntervalsForSpills(*li, spillIs, loopInfo, *vrm);
+  void spill(LiveInterval *li,
+             std::vector<LiveInterval*> &newIntervals,
+             SmallVectorImpl<LiveInterval*> &spillIs,
+             SlotIndex*) {
+    std::vector<LiveInterval*> added =
+      lis->addIntervalsForSpills(*li, spillIs, loopInfo, *vrm);
+    newIntervals.insert(newIntervals.end(), added.begin(), added.end());
   }
 };
 
@@ -226,15 +227,14 @@ public:
     tri = mf->getTarget().getRegisterInfo();
   }
 
-  std::vector<LiveInterval*> spill(LiveInterval *li,
-                                   SmallVectorImpl<LiveInterval*> &spillIs,
-                                   SlotIndex *earliestStart) {
-    
-    if (worthTryingToSplit(li)) {
-      return tryVNISplit(li, earliestStart);
-    }
-    // else
-    return StandardSpiller::spill(li, spillIs, earliestStart);
+  void spill(LiveInterval *li,
+             std::vector<LiveInterval*> &newIntervals,
+             SmallVectorImpl<LiveInterval*> &spillIs,
+             SlotIndex *earliestStart) {
+    if (worthTryingToSplit(li))
+      tryVNISplit(li, earliestStart);
+    else
+      StandardSpiller::spill(li, newIntervals, spillIs, earliestStart);
   }
 
 private:

lib/CodeGen/Spiller.h

@@ -33,11 +33,19 @@ namespace llvm {
   public:
     virtual ~Spiller() = 0;
 
-    /// Spill the given live range. The method used will depend on the Spiller
-    /// implementation selected.
-    virtual std::vector<LiveInterval*> spill(LiveInterval *li,
-					     SmallVectorImpl<LiveInterval*> &spillIs,
-                                             SlotIndex *earliestIndex = 0) = 0;
+    /// spill - Spill the given live interval. The method used will depend on
+    /// the Spiller implementation selected.
+    ///
+    /// @param li            The live interval to be spilled.
+    /// @param spillIs       An essential hook into the register allocator guts
+    ///                      that perhaps serves a purpose(?!)
+    /// @param newIntervals  The newly created intervals will be appended here.
+    /// @param earliestIndex The earliest point for splitting. (OK, it's another
+    ///                      pointer to the allocator guts).
+    virtual void spill(LiveInterval *li,
+                       std::vector<LiveInterval*> &newIntervals,
+                       SmallVectorImpl<LiveInterval*> &spillIs,
+                       SlotIndex *earliestIndex = 0) = 0;
 
   };