JIT: Remove compaction renumbering quirk (dotnet#96478)

src/coreclr/jit/compiler.cpp

@@ -4849,8 +4849,7 @@ void Compiler::compCompile(void** methodCodePtr, uint32_t* methodCodeSize, JitFl
         optLoopCount      = 0;
 
         // Old dominators and reachability sets are no longer valid.
-        fgDomsComputed         = false;
-        fgCompactRenumberQuirk = true;
+        fgDomsComputed = false;
     }
 
 #ifdef DEBUG
@@ -5039,7 +5038,6 @@ void Compiler::compCompile(void** methodCodePtr, uint32_t* methodCodeSize, JitFl
     }
 
     optLoopsRequirePreHeaders = false;
-    fgCompactRenumberQuirk    = false;
 
 #ifdef DEBUG
     DoPhase(this, PHASE_STRESS_SPLIT_TREE, &Compiler::StressSplitTree);

src/coreclr/jit/compiler.h

@@ -5124,7 +5124,6 @@ class Compiler
     bool fgReturnBlocksComputed; // Have we computed the return blocks list?
     bool fgOptimizedFinally;     // Did we optimize any try-finallys?
     bool fgCanonicalizedFirstBB; // TODO-Quirk: did we end up canonicalizing first BB?
-    bool fgCompactRenumberQuirk; // TODO-Quirk: Should fgCompactBlocks renumber BBs above fgDomBBcount?
 
     bool fgHasSwitch; // any BBJ_SWITCH jumps?
 

src/coreclr/jit/fgbasic.cpp

@@ -33,7 +33,6 @@ void Compiler::fgInit()
     /* We haven't yet computed the dominator sets */
     fgDomsComputed         = false;
     fgReturnBlocksComputed = false;
-    fgCompactRenumberQuirk = false;
 
 #ifdef DEBUG
     fgReachabilitySetsValid = false;

src/coreclr/jit/fgopt.cpp

@@ -2356,54 +2356,7 @@ void Compiler::fgCompactBlocks(BasicBlock* block, BasicBlock* bNext)
         block->RemoveFlags(BBF_NONE_QUIRK);
     }
 
-    // If we're collapsing a block created after the dominators are
-    // computed, copy block number the block and reuse dominator
-    // information from bNext to block.
-    //
-    // Note we have to do this renumbering after the full set of pred list
-    // updates above, since those updates rely on stable bbNums; if we renumber
-    // before the updates, we can create pred lists with duplicate m_block->bbNum
-    // values (though different m_blocks).
-    //
-    if ((fgDomsComputed || fgCompactRenumberQuirk) && (block->bbNum > fgDomBBcount))
-    {
-        if (fgDomsComputed)
-        {
-            assert(fgReachabilitySetsValid);
-            BlockSetOps::Assign(this, block->bbReach, bNext->bbReach);
-            BlockSetOps::ClearD(this, bNext->bbReach);
-
-            block->bbIDom = bNext->bbIDom;
-            bNext->bbIDom = nullptr;
-
-            // In this case, there's no need to update the preorder and postorder numbering
-            // since we're changing the bbNum, this makes the basic block all set.
-            //
-            JITDUMP("Renumbering " FMT_BB " to be " FMT_BB " to preserve dominator information\n", block->bbNum,
-                    bNext->bbNum);
-        }
-        else
-        {
-            // TODO-Quirk: Remove
-            JITDUMP("Renumbering " FMT_BB " to be " FMT_BB " for a quirk\n", block->bbNum, bNext->bbNum);
-        }
-
-        block->bbNum = bNext->bbNum;
-
-        // Because we may have reordered pred lists when we swapped in
-        // block for bNext above, we now need to re-reorder pred lists
-        // to reflect the bbNum update.
-        //
-        // This process of reordering and re-reordering could likely be avoided
-        // via a different update strategy. But because it's probably rare,
-        // and we avoid most of the work if pred lists are already in order,
-        // we'll just ensure everything is properly ordered.
-        //
-        for (BasicBlock* const checkBlock : Blocks())
-        {
-            checkBlock->ensurePredListOrder(this);
-        }
-    }
+    assert(!fgDomsComputed);
 
     if (optLoopTableValid)
     {

src/coreclr/jit/optimizer.cpp

@@ -4590,8 +4590,7 @@ PhaseStatus Compiler::optUnrollLoops()
     optLoopCount      = 0;
 
     // Old dominators and reachability sets are no longer valid.
-    fgDomsComputed         = false;
-    fgCompactRenumberQuirk = true;
+    fgDomsComputed = false;
 
     return anyIRchange ? PhaseStatus::MODIFIED_EVERYTHING : PhaseStatus::MODIFIED_NOTHING;
 }