Added a new "splitting" spiller.

When a call is placed to spill an interval this spiller will first try to
break the interval up into its component values. Single value intervals and
intervals which have already been split (or are the result of previous splits)
are spilled by the default spiller.

Splitting intervals as described above may improve the performance of generated
code in some circumstances. This work is experimental however, and it still
miscompiles many benchmarks. It's not recommended for general use yet.

llvm-svn: 90951

1 files changed, 6 insertions, 9 deletions

diff --git a/llvm/lib/CodeGen/RegAllocLinearScan.cpp b/llvm/lib/CodeGen/RegAllocLinearScan.cpp
index 4ff512932f8..c1f587567e8 100644
--- a/llvm/lib/CodeGen/RegAllocLinearScan.cpp
+++ b/llvm/lib/CodeGen/RegAllocLinearScan.cpp
@@ -1261,9 +1261,9 @@ void RALinScan::assignRegOrStackSlotAtInterval(LiveInterval* cur) {
 
   // The earliest start of a Spilled interval indicates up to where
   // in handled we need to roll back
+  assert(!spillIs.empty() && "No spill intervals?"); 
+  SlotIndex earliestStart = spillIs[0]->beginIndex();
   
-  LiveInterval *earliestStartInterval = cur;
-
   // Spill live intervals of virtual regs mapped to the physical register we
   // want to clear (and its aliases).  We only spill those that overlap with the
   // current interval as the rest do not affect its allocation. we also keep
@@ -1274,19 +1274,16 @@ void RALinScan::assignRegOrStackSlotAtInterval(LiveInterval* cur) {
     LiveInterval *sli = spillIs.back();
     spillIs.pop_back();
     DEBUG(errs() << "\t\t\tspilling(a): " << *sli << '\n');
-    earliestStartInterval =
-      (earliestStartInterval->beginIndex() < sli->beginIndex()) ?
-         earliestStartInterval : sli;
+    if (sli->beginIndex() < earliestStart)
+      earliestStart = sli->beginIndex();
        
     std::vector<LiveInterval*> newIs;
-    newIs = spiller_->spill(sli, spillIs);
+    newIs = spiller_->spill(sli, spillIs, &earliestStart);
     addStackInterval(sli, ls_, li_, mri_, *vrm_);
     std::copy(newIs.begin(), newIs.end(), std::back_inserter(added));
     spilled.insert(sli->reg);
   }
 
-  SlotIndex earliestStart = earliestStartInterval->beginIndex();
-
   DEBUG(errs() << "\t\trolling back to: " << earliestStart << '\n');
 
   // Scan handled in reverse order up to the earliest start of a
@@ -1295,7 +1292,7 @@ void RALinScan::assignRegOrStackSlotAtInterval(LiveInterval* cur) {
   while (!handled_.empty()) {
     LiveInterval* i = handled_.back();
     // If this interval starts before t we are done.
-    if (i->beginIndex() < earliestStart)
+    if (!i->empty() && i->beginIndex() < earliestStart)
       break;
     DEBUG(errs() << "\t\t\tundo changes for: " << *i << '\n');
     handled_.pop_back();