Move ObjectAllocator phase to run right after inlining. (#20377)

This change will support object stack allocation for the following reasons:

1. Objects should be allocated on the stack before struct promotion phase
so that their fields have a chance to be promoted.
2. Eventually object stack allocation will be performed in the same phase
as inlining since inlining heuristics will need to be aware of object stack allocation
opportunities.

I verified no x64 diffs with jit-diffs --frameworks --tests --pmi

Author: erozenfeld

src/jit/compiler.cpp

@@ -4665,11 +4665,6 @@ void Compiler::compCompile(void** methodCodePtr, ULONG* methodCodeSize, JitFlags
         EndPhase(PHASE_COMPUTE_REACHABILITY);
     }
 
-    // Transform each GT_ALLOCOBJ node into either an allocation helper call or
-    // local variable allocation on the stack.
-    ObjectAllocator objectAllocator(this);
-    objectAllocator.Run();
-
     if (!opts.MinOpts() && !opts.compDbgCode)
     {
         /*  Perform loop inversion (i.e. transform "while" loops into

src/jit/compiler.h

@@ -5012,7 +5012,7 @@ class Compiler
 
     GenTree* fgMorphCastIntoHelper(GenTree* tree, int helper, GenTree* oper);
 
-    GenTree* fgMorphIntoHelperCall(GenTree* tree, int helper, GenTreeArgList* args);
+    GenTree* fgMorphIntoHelperCall(GenTree* tree, int helper, GenTreeArgList* args, bool morphArgs = true);
 
     GenTree* fgMorphStackArgForVarArgs(unsigned lclNum, var_types varType, unsigned lclOffs);
 

src/jit/compphases.h

@@ -29,6 +29,7 @@ CompPhaseNameMacro(PHASE_IMPORTATION,            "Importation",
 CompPhaseNameMacro(PHASE_POST_IMPORT,            "Post-import",                    "POST-IMP", false, -1, false)
 CompPhaseNameMacro(PHASE_MORPH_INIT,             "Morph - Init",                   "MOR-INIT" ,false, -1, false)
 CompPhaseNameMacro(PHASE_MORPH_INLINE,           "Morph - Inlining",               "MOR-INL",  false, -1, true)
+CompPhaseNameMacro(PHASE_ALLOCATE_OBJECTS,       "Allocate Objects",               "ALLOC-OBJ", false, -1, false)
 CompPhaseNameMacro(PHASE_EMPTY_TRY,              "Remove empty try",               "EMPTYTRY", false, -1, false)
 CompPhaseNameMacro(PHASE_EMPTY_FINALLY,          "Remove empty finally",           "EMPTYFIN", false, -1, false)
 CompPhaseNameMacro(PHASE_MERGE_FINALLY_CHAINS,   "Merge callfinally chains",       "MRGCFCHN", false, -1, false)
@@ -46,7 +47,6 @@ CompPhaseNameMacro(PHASE_CREATE_FUNCLETS,        "Create EH funclets",
 #endif // FEATURE_EH_FUNCLETS
 CompPhaseNameMacro(PHASE_OPTIMIZE_LAYOUT,        "Optimize layout",                "LAYOUT",   false, -1, false)
 CompPhaseNameMacro(PHASE_COMPUTE_REACHABILITY,   "Compute blocks reachability",    "BL_REACH", false, -1, false)
-CompPhaseNameMacro(PHASE_ALLOCATE_OBJECTS,       "Allocate Objects",               "ALLOC-OBJ",false, -1, false)
 CompPhaseNameMacro(PHASE_OPTIMIZE_LOOPS,         "Optimize loops",                 "LOOP-OPT", false, -1, false)
 CompPhaseNameMacro(PHASE_CLONE_LOOPS,            "Clone loops",                    "LP-CLONE", false, -1, false)
 CompPhaseNameMacro(PHASE_UNROLL_LOOPS,           "Unroll loops",                   "UNROLL",   false, -1, false)

src/jit/morph.cpp

@@ -58,7 +58,7 @@ GenTree* Compiler::fgMorphCastIntoHelper(GenTree* tree, int helper, GenTree* ope
  *  the given argument list.
  */
 
-GenTree* Compiler::fgMorphIntoHelperCall(GenTree* tree, int helper, GenTreeArgList* args)
+GenTree* Compiler::fgMorphIntoHelperCall(GenTree* tree, int helper, GenTreeArgList* args, bool morphArgs)
 {
     // The helper call ought to be semantically equivalent to the original node, so preserve its VN.
     tree->ChangeOper(GT_CALL, GenTree::PRESERVE_VN);
@@ -112,7 +112,10 @@ GenTree* Compiler::fgMorphIntoHelperCall(GenTree* tree, int helper, GenTreeArgLi
 
     /* Perform the morphing */
 
-    tree = fgMorphArgs(tree->AsCall());
+    if (morphArgs)
+    {
+        tree = fgMorphArgs(tree->AsCall());
+    }
 
     return tree;
 }
@@ -16873,6 +16876,11 @@ void Compiler::fgMorph()
 
     EndPhase(PHASE_MORPH_INLINE);
 
+    // Transform each GT_ALLOCOBJ node into either an allocation helper call or
+    // local variable allocation on the stack.
+    ObjectAllocator objectAllocator(this); // PHASE_ALLOCATE_OBJECTS
+    objectAllocator.Run();
+
     /* Add any internal blocks/trees we may need */
 
     fgAddInternal();

src/jit/objectalloc.cpp

@@ -155,7 +155,9 @@ GenTree* ObjectAllocator::MorphAllocObjNodeIntoHelperCall(GenTreeAllocObj* alloc
 
     GenTree* op1 = allocObj->gtGetOp1();
 
-    GenTree* helperCall = comp->fgMorphIntoHelperCall(allocObj, allocObj->gtNewHelper, comp->gtNewArgList(op1));
+    const bool morphArgs = false;
+    GenTree*   helperCall =
+        comp->fgMorphIntoHelperCall(allocObj, allocObj->gtNewHelper, comp->gtNewArgList(op1), morphArgs);
 
     return helperCall;
 }

src/jit/objectalloc.h

@@ -53,6 +53,9 @@ inline ObjectAllocator::ObjectAllocator(Compiler* comp)
     , m_IsObjectStackAllocationEnabled(false)
     , m_AnalysisDone(false)
 {
+    // Disable checks since this phase runs before fgComputePreds phase.
+    // Checks are not expected to pass before fgComputePreds.
+    doChecks = false;
 }
 
 inline bool ObjectAllocator::IsObjectStackAllocationEnabled() const

src/jit/phase.h

@@ -12,7 +12,8 @@ class Phase
     virtual void Run();
 
 protected:
-    Phase(Compiler* _comp, const char* _name, Phases _phase = PHASE_NUMBER_OF) : comp(_comp), name(_name), phase(_phase)
+    Phase(Compiler* _comp, const char* _name, Phases _phase = PHASE_NUMBER_OF)
+        : comp(_comp), name(_name), phase(_phase), doChecks(true)
     {
     }
 
@@ -23,6 +24,7 @@ class Phase
     Compiler*   comp;
     const char* name;
     Phases      phase;
+    bool        doChecks;
 };
 
 inline void Phase::Run()
@@ -42,7 +44,7 @@ inline void Phase::PrePhase()
         comp->fgDispBasicBlocks(true);
     }
 
-    if (comp->expensiveDebugCheckLevel >= 2)
+    if (doChecks && comp->expensiveDebugCheckLevel >= 2)
     {
         // If everyone used the Phase class, this would duplicate the PostPhase() from the previous phase.
         // But, not everyone does, so go ahead and do the check here, too.
@@ -69,8 +71,11 @@ inline void Phase::PostPhase()
     }
 
 #ifdef DEBUG
-    comp->fgDebugCheckBBlist();
-    comp->fgDebugCheckLinks();
+    if (doChecks)
+    {
+        comp->fgDebugCheckBBlist();
+        comp->fgDebugCheckLinks();
+    }
 #endif // DEBUG
 }