[PATCH] D145864: [CodeGen] Introduce threshold option to constrain stack slot sharing during stack coloring.

[Valery Pykhtin via Phabricator via llvm-commits]

vpykhtin created this revision.
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AMDGPU code with enabled address sanitizer generates tons of stack objects (> 200000) and
takes forever to compile due to the time spent on slot sharing.

I made up the threshold value, not sure what it should be (apparently more than 42) but
on the other hand - the more stack objects you have the more useful is sharing.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D145864

Files:
  llvm/lib/CodeGen/StackSlotColoring.cpp


Index: llvm/lib/CodeGen/StackSlotColoring.cpp
===================================================================
--- llvm/lib/CodeGen/StackSlotColoring.cpp
+++ llvm/lib/CodeGen/StackSlotColoring.cpp
@@ -50,6 +50,12 @@
              cl::init(false), cl::Hidden,
              cl::desc("Suppress slot sharing during stack coloring"));
 
+static cl::opt<unsigned>
+    SlotSharingThreshold("-stack-slot-sharing-threshold", cl::init(1000),
+                         cl::Hidden,
+                         cl::desc("Suppress slot sharing during stack coloring "
+                                  "if the number of slots exceeds this value"));
+
 static cl::opt<int> DCELimit("ssc-dce-limit", cl::init(-1), cl::Hidden);
 
 STATISTIC(NumEliminated, "Number of stack slots eliminated due to coloring");
@@ -117,7 +123,7 @@
     void InitializeSlots();
     void ScanForSpillSlotRefs(MachineFunction &MF);
     bool OverlapWithAssignments(LiveInterval *li, int Color) const;
-    int ColorSlot(LiveInterval *li);
+    int ColorSlot(LiveInterval *li, bool TryShareSlots = true);
     bool ColorSlots(MachineFunction &MF);
     void RewriteInstruction(MachineInstr &MI, SmallVectorImpl<int> &SlotMapping,
                             MachineFunction &MF);
@@ -261,13 +267,13 @@
 }
 
 /// ColorSlot - Assign a "color" (stack slot) to the specified stack slot.
-int StackSlotColoring::ColorSlot(LiveInterval *li) {
+int StackSlotColoring::ColorSlot(LiveInterval *li, bool TryShareSlots) {
   int Color = -1;
   bool Share = false;
   int FI = Register::stackSlot2Index(li->reg());
   uint8_t StackID = MFI->getStackID(FI);
 
-  if (!DisableSharing) {
+  if (TryShareSlots) {
 
     // Check if it's possible to reuse any of the used colors.
     Color = UsedColors[StackID].find_first();
@@ -321,12 +327,14 @@
   SmallVector<float, 16> SlotWeights(NumObjs, 0.0);
   SmallVector<SmallVector<int, 4>, 16> RevMap(NumObjs);
   BitVector UsedColors(NumObjs);
+  const bool TryShareSlots =
+      !DisableSharing && SSIntervals.size() < SlotSharingThreshold;
 
   LLVM_DEBUG(dbgs() << "Color spill slot intervals:\n");
   bool Changed = false;
   for (LiveInterval *li : SSIntervals) {
     int SS = Register::stackSlot2Index(li->reg());
-    int NewSS = ColorSlot(li);
+    int NewSS = ColorSlot(li, TryShareSlots);
     assert(NewSS >= 0 && "Stack coloring failed?");
     SlotMapping[SS] = NewSS;
     RevMap[NewSS].push_back(SS);


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