JIT: build pred lists before object allocation phase (#80891)

Move the pred list building up a bit further.

Contributes to #80193.

Author: AndyAyersMS

src/coreclr/jit/compiler.cpp

@@ -4467,21 +4467,6 @@ void Compiler::compCompile(void** methodCodePtr, uint32_t* methodCodeSize, JitFl
     // Record "start" values for post-inlining cycles and elapsed time.
     RecordStateAtEndOfInlining();
 
-    // Transform each GT_ALLOCOBJ node into either an allocation helper call or
-    // local variable allocation on the stack.
-    ObjectAllocator objectAllocator(this); // PHASE_ALLOCATE_OBJECTS
-
-    if (compObjectStackAllocation() && opts.OptimizationEnabled())
-    {
-        objectAllocator.EnableObjectStackAllocation();
-    }
-
-    objectAllocator.Run();
-
-    // Add any internal blocks/trees we may need
-    //
-    DoPhase(this, PHASE_MORPH_ADD_INTERNAL, &Compiler::fgAddInternal);
-
     // Compute bbNum, bbRefs and bbPreds
     //
     // This is the first time full (not cheap) preds will be computed.
@@ -4500,6 +4485,21 @@ void Compiler::compCompile(void** methodCodePtr, uint32_t* methodCodeSize, JitFl
     };
     DoPhase(this, PHASE_COMPUTE_PREDS, computePredsPhase);
 
+    // Transform each GT_ALLOCOBJ node into either an allocation helper call or
+    // local variable allocation on the stack.
+    ObjectAllocator objectAllocator(this); // PHASE_ALLOCATE_OBJECTS
+
+    if (compObjectStackAllocation() && opts.OptimizationEnabled())
+    {
+        objectAllocator.EnableObjectStackAllocation();
+    }
+
+    objectAllocator.Run();
+
+    // Add any internal blocks/trees we may need
+    //
+    DoPhase(this, PHASE_MORPH_ADD_INTERNAL, &Compiler::fgAddInternal);
+
     // Remove empty try regions
     //
     DoPhase(this, PHASE_EMPTY_TRY, &Compiler::fgRemoveEmptyTry);

src/coreclr/jit/flowgraph.cpp

@@ -1565,8 +1565,8 @@ void Compiler::fgAddSyncMethodEnterExit()
     // We need to do this transformation before funclets are created.
     assert(!fgFuncletsCreated);
 
-    // Assume we don't need to update the bbPreds lists.
-    assert(!fgComputePredsDone);
+    // We need to update the bbPreds lists.
+    assert(fgComputePredsDone);
 
 #if !FEATURE_EH
     // If we don't support EH, we can't add the EH needed by synchronized methods.
@@ -1595,6 +1595,7 @@ void Compiler::fgAddSyncMethodEnterExit()
     }
 
     // Create a block for the fault.
+    // It gets an artificial ref count.
 
     assert(!tryLastBB->bbFallsThrough());
     BasicBlock* faultBB = fgNewBBafter(BBJ_EHFINALLYRET, tryLastBB, false);
@@ -1603,6 +1604,8 @@ void Compiler::fgAddSyncMethodEnterExit()
     assert(faultBB->bbNext == nullptr);
     assert(faultBB == fgLastBB);
 
+    faultBB->bbRefs = 1;
+
     { // Scope the EH region creation
 
         // Add the new EH region at the end, since it is the least nested,
@@ -2184,7 +2187,6 @@ class MergedReturns
     BasicBlock* CreateReturnBB(unsigned index, GenTreeIntConCommon* returnConst = nullptr)
     {
         BasicBlock* newReturnBB = comp->fgNewBBinRegion(BBJ_RETURN);
-        newReturnBB->bbRefs     = 1; // bbRefs gets update later, for now it should be 1
         comp->fgReturnCount++;
 
         noway_assert(newReturnBB->bbNext == nullptr);
@@ -2344,6 +2346,7 @@ class MergedReturns
                     assert((comp->info.compFlags & CORINFO_FLG_SYNCH) == 0);
                     returnBlock->bbJumpKind = BBJ_ALWAYS;
                     returnBlock->bbJumpDest = constReturnBlock;
+                    comp->fgAddRefPred(constReturnBlock, returnBlock);
 
                     // Remove GT_RETURN since constReturnBlock returns the constant.
                     assert(returnBlock->lastStmt()->GetRootNode()->OperIs(GT_RETURN));