Remove bloating in map

Author: Pierre-vh

llvm/lib/Target/AMDGPU/SIInsertWaitcnts.cpp

@@ -704,8 +704,11 @@ class WaitcntBrackets {
 
   void clearVgprVmemTypes(MCPhysReg Reg) {
     for (MCRegUnit RU : regunits(Reg)) {
-      if (auto It = VMem.find(toVMEMID(RU)); It != VMem.end())
+      if (auto It = VMem.find(toVMEMID(RU)); It != VMem.end()) {
         It->second.VMEMTypes = 0;
+        if (It->second.empty())
+          VMem.erase(It);
+      }
     }
   }
 
@@ -726,6 +729,10 @@ class WaitcntBrackets {
   void print(raw_ostream &) const;
   void dump() const { print(dbgs()); }
 
+  // Free up memory by removing empty entries from the DenseMap that track event
+  // scores.
+  void purgeEmptyTrackingData();
+
 private:
   struct MergeInfo {
     unsigned OldLB;
@@ -813,17 +820,23 @@ class WaitcntBrackets {
 
   struct VGPRInfo {
     // Scores for all instruction counters.
-    unsigned Scores[NUM_INST_CNTS] = {0};
+    std::array<unsigned, NUM_INST_CNTS> Scores = {0};
     // Bitmask of the VmemTypes of VMEM instructions for this VGPR.
     unsigned VMEMTypes = 0;
+
+    bool empty() const {
+      return all_of(Scores, [](unsigned K) { return K == 0; }) && !VMEMTypes;
+    }
   };
 
   struct SGPRInfo {
     // Wait cnt scores for every sgpr, the DS_CNT (corresponding to LGKMcnt
     // pre-gfx12) or KM_CNT (gfx12+ only), and X_CNT (gfx1250) are relevant.
     // Row 0 represents the score for either DS_CNT or KM_CNT and row 1 keeps
     // the X_CNT score.
-    unsigned Scores[2] = {0};
+    std::array<unsigned, 2> Scores = {0};
+
+    bool empty() const { return !Scores[0] && !Scores[1]; }
   };
 
   DenseMap<VMEMID, VGPRInfo> VMem; // VGPR + LDS DMA
@@ -1196,6 +1209,17 @@ void WaitcntBrackets::simplifyWaitcnt(InstCounterType T,
     Count = ~0u;
 }
 
+void WaitcntBrackets::purgeEmptyTrackingData() {
+  for (auto &[K, V] : make_early_inc_range(VMem)) {
+    if (V.empty())
+      VMem.erase(K);
+  }
+  for (auto &[K, V] : make_early_inc_range(SGPRs)) {
+    if (V.empty())
+      SGPRs.erase(K);
+  }
+}
+
 void WaitcntBrackets::determineWaitForScore(InstCounterType T,
                                             unsigned ScoreToWait,
                                             AMDGPU::Waitcnt &Wait) const {
@@ -2435,6 +2459,7 @@ bool WaitcntBrackets::merge(const WaitcntBrackets &Other) {
     Value.VMEMTypes = NewVmemTypes;
   }
 
+  purgeEmptyTrackingData();
   return StrictDom;
 }