JIT: Remove some fgRenumberBlocks calls

src/coreclr/jit/compiler.cpp

@@ -4761,13 +4761,6 @@ void Compiler::compCompile(void** methodCodePtr, uint32_t* methodCodeSize, JitFl
     };
     DoPhase(this, PHASE_POST_MORPH, postMorphPhase);
 
-    // If we needed to create any new BasicBlocks then renumber the blocks
-    //
-    if (fgBBcount > preMorphBBCount)
-    {
-        fgRenumberBlocks();
-    }
-
     // GS security checks for unsafe buffers
     //
     DoPhase(this, PHASE_GS_COOKIE, &Compiler::gsPhase);
@@ -4928,6 +4921,15 @@ void Compiler::compCompile(void** methodCodePtr, uint32_t* methodCodeSize, JitFl
 
             if (doLoopHoisting)
             {
+                if (doBranchOpt)
+                {
+                    // bbNum quirk: RBO uses the current BB epoch size to determine if loop hoisting created blocks.
+                    // Ensure the BB epoch is up to date before running loop hoisting to avoid false positives.
+                    // TODO-bbNum: Either replace this check with a breadcrumb like 'fgModified',
+                    // or relax jump threading's prerequisites.
+                    EnsureBasicBlockEpoch();
+                }
+
                 // Hoist invariant code out of loops
                 //
                 DoPhase(this, PHASE_HOIST_LOOP_CODE, &Compiler::optHoistLoopCode);
@@ -5888,8 +5890,6 @@ void Compiler::RecomputeFlowGraphAnnotations()
     // Recompute reachability sets, dominators, and loops.
     optResetLoopInfo();
 
-    fgRenumberBlocks();
-    fgInvalidateDfsTree();
     fgDfsBlocksAndRemove();
     optFindLoops();
 

src/coreclr/jit/fginline.cpp

@@ -913,14 +913,6 @@ PhaseStatus Compiler::fgInline()
 
 #endif // DEBUG
 
-    if (madeChanges)
-    {
-        // Optional quirk to keep this as zero diff. Some downstream phases are bbNum sensitive
-        // but rely on the ambient bbNums.
-        //
-        fgRenumberBlocks();
-    }
-
     if (fgPgoConsistent)
     {
         Metrics.ProfileConsistentAfterInline++;

src/coreclr/jit/fgopt.cpp

@@ -752,25 +752,13 @@ PhaseStatus Compiler::fgPostImportationCleanup()
         }
     }
 
-    // Did we alter any flow or EH?
-    //
-    const bool madeFlowChanges = (addedBlocks > 0) || (delCnt > 0) || (removedBlks > 0);
-
-    // Renumber the basic blocks if so.
-    //
-    if (madeFlowChanges)
-    {
-        JITDUMP("\nRenumbering the basic blocks for fgPostImportationCleanup\n");
-        fgRenumberBlocks();
-    }
-
 #ifdef DEBUG
     fgVerifyHandlerTab();
 #endif // DEBUG
 
     // Did we make any changes?
     //
-    const bool madeChanges = madeFlowChanges || addedTemps;
+    const bool madeChanges = (addedBlocks > 0) || (delCnt > 0) || (removedBlks > 0) || addedTemps;
 
     // Note that we have now run post importation cleanup,
     // so we can enable more stringent checking.

src/coreclr/jit/flowgraph.cpp

@@ -152,13 +152,8 @@ PhaseStatus Compiler::fgInsertGCPolls()
         block = curBasicBlock;
     }
 
-    // If we split a block to create a GC Poll, call fgUpdateChangedFlowGraph.
     // We should never split blocks unless we're optimizing.
-    if (createdPollBlocks)
-    {
-        noway_assert(opts.OptimizationEnabled());
-        fgRenumberBlocks();
-    }
+    assert(!createdPollBlocks || opts.OptimizationEnabled());
 
     return result;
 }

src/coreclr/jit/gschecks.cpp

@@ -35,12 +35,6 @@ PhaseStatus Compiler::gsPhase()
             gsCopyShadowParams();
         }
 
-        // If we needed to create any new BasicBlocks then renumber the blocks
-        if (fgBBcount > prevBBCount)
-        {
-            fgRenumberBlocks();
-        }
-
         madeChanges = true;
     }
     else

src/coreclr/jit/helperexpansion.cpp

@@ -1225,11 +1225,6 @@ PhaseStatus Compiler::fgExpandHelper(bool skipRarelyRunBlocks)
     if (result == PhaseStatus::MODIFIED_EVERYTHING)
     {
         fgInvalidateDfsTree();
-
-        if (opts.OptimizationEnabled())
-        {
-            fgRenumberBlocks();
-        }
     }
 
     return result;

src/coreclr/jit/jiteh.cpp

@@ -2123,8 +2123,8 @@ void Compiler::fgNormalizeEH()
     if (modified)
     {
         JITDUMP("Added at least one basic block in fgNormalizeEH.\n");
-        fgRenumberBlocks();
-        // fgRenumberBlocks() will dump all the blocks and the handler table, so we don't need to do it here.
+        JITDUMPEXEC(fgDispBasicBlocks());
+        JITDUMPEXEC(fgDispHandlerTab());
         INDEBUG(fgVerifyHandlerTab());
     }
     else

src/coreclr/jit/optimizer.cpp

@@ -40,6 +40,7 @@ DataFlow::DataFlow(Compiler* pCompiler)
 PhaseStatus Compiler::optSetBlockWeights()
 {
     noway_assert(opts.OptimizationEnabled());
+    bool madeChanges = false;
 
     assert(m_dfsTree != nullptr);
     if (m_domTree == nullptr)
@@ -53,11 +54,11 @@ PhaseStatus Compiler::optSetBlockWeights()
 
     if (m_dfsTree->HasCycle())
     {
+        madeChanges = fgRenumberBlocks();
         optMarkLoopHeads();
         optFindAndScaleGeneralLoopBlocks();
     }
 
-    bool       madeChanges                = false;
     bool       firstBBDominatesAllReturns = true;
     const bool usingProfileWeights        = fgIsUsingProfileWeights();
 
@@ -1335,13 +1336,11 @@ PhaseStatus Compiler::optUnrollLoops()
             m_loops   = FlowGraphNaturalLoops::Find(m_dfsTree);
         }
 
-        fgRenumberBlocks();
-
         DBEXEC(verbose, fgDispBasicBlocks());
     }
 
 #ifdef DEBUG
-    fgDebugCheckBBlist(true);
+    fgDebugCheckBBlist();
 #endif // DEBUG
 
     return anyIRchange ? PhaseStatus::MODIFIED_EVERYTHING : PhaseStatus::MODIFIED_NOTHING;
@@ -2687,8 +2686,6 @@ PhaseStatus Compiler::optFindLoopsPhase()
     }
 #endif
 
-    fgRenumberBlocks();
-
     assert(m_dfsTree != nullptr);
     optFindLoops();
 
@@ -2713,8 +2710,6 @@ void Compiler::optFindLoops()
         m_loops   = FlowGraphNaturalLoops::Find(m_dfsTree);
     }
 
-    fgRenumberBlocks();
-
     // Starting now we require all loops to be in canonical form.
     optLoopsCanonical = true;