JIT: Propagate physical promotion liveness in post-order (#104554)

We now have a DFS tree available in physical promotion. This mean that like normal liveness we can maximize the information propagated on every iteration by running physical promotion's dataflow in post-order.
dotnet · Jul 8, 2024 · a0f0c6c · a0f0c6c
1 parent 8b9ea5e
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Showing 2 changed files with 6 additions and 12 deletions.
diff --git a/src/coreclr/jit/promotion.h b/src/coreclr/jit/promotion.h
@@ -200,7 +200,6 @@ class PromotionLiveness
     unsigned*                                               m_structLclToTrackedIndex = nullptr;
     unsigned                                                m_numVars                 = 0;
     BasicBlockLiveness*                                     m_bbInfo                  = nullptr;
-    bool                                                    m_hasPossibleBackEdge     = false;
     BitVec                                                  m_liveIn;
     BitVec                                                  m_ehLiveVars;
     JitHashTable<GenTree*, JitPtrKeyFuncs<GenTree>, BitVec> m_aggDeaths;

diff --git a/src/coreclr/jit/promotionliveness.cpp b/src/coreclr/jit/promotionliveness.cpp
@@ -294,22 +294,19 @@ void PromotionLiveness::MarkIndex(unsigned index, bool isUse, bool isDef, BitVec
 //
 void PromotionLiveness::InterBlockLiveness()
 {
+    FlowGraphDfsTree* dfsTree = m_compiler->m_dfsTree;
+    assert(dfsTree != nullptr);
+
     bool changed;
     do
     {
         changed = false;
 
-        for (BasicBlock* block = m_compiler->fgLastBB; block != nullptr; block = block->Prev())
-        {
-            m_hasPossibleBackEdge |= !block->IsLast() && (block->Next()->bbNum <= block->bbNum);
-            changed |= PerBlockLiveness(block);
-        }
-
-        if (!m_hasPossibleBackEdge)
+        for (unsigned i = 0; i < dfsTree->GetPostOrderCount(); i++)
         {
-            break;
+            changed |= PerBlockLiveness(dfsTree->GetPostOrder(i));
         }
-    } while (changed);
+    } while (changed && dfsTree->HasCycle());
 
 #ifdef DEBUG
     if (m_compiler->verbose)
@@ -345,7 +342,6 @@ bool PromotionLiveness::PerBlockLiveness(BasicBlock* block)
     BitVecOps::ClearD(m_bvTraits, bbInfo.LiveOut);
     block->VisitRegularSuccs(m_compiler, [=, &bbInfo](BasicBlock* succ) {
         BitVecOps::UnionD(m_bvTraits, bbInfo.LiveOut, m_bbInfo[succ->bbNum].LiveIn);
-        m_hasPossibleBackEdge |= succ->bbNum <= block->bbNum;
         return BasicBlockVisit::Continue;
     });
 
@@ -357,7 +353,6 @@ bool PromotionLiveness::PerBlockLiveness(BasicBlock* block)
         AddHandlerLiveVars(block, m_ehLiveVars);
         BitVecOps::UnionD(m_bvTraits, m_liveIn, m_ehLiveVars);
         BitVecOps::UnionD(m_bvTraits, bbInfo.LiveOut, m_ehLiveVars);
-        m_hasPossibleBackEdge = true;
     }
 
     bool liveInChanged = !BitVecOps::Equal(m_bvTraits, bbInfo.LiveIn, m_liveIn);