Remove compLvFrameListRoot special-casing from liveness

This is referenced explicitly from IR generated by lowering.

Author: SingleAccretion

src/coreclr/jit/compiler.cpp

@@ -9925,10 +9925,6 @@ JITDBGAPI void __cdecl cTreeFlags(Compiler* comp, GenTree* tree)
                         }
                     }
 
-                    if (call->gtCallMoreFlags & GTF_CALL_M_FRAME_VAR_DEATH)
-                    {
-                        chars += printf("[CALL_M_FRAME_VAR_DEATH]");
-                    }
                     if (call->gtCallMoreFlags & GTF_CALL_M_TAILCALL_VIA_JIT_HELPER)
                     {
                         chars += printf("[CALL_M_TAILCALL_VIA_JIT_HELPER]");

src/coreclr/jit/gentree.cpp

@@ -13145,11 +13145,6 @@ void Compiler::gtDispTree(GenTree*                    tree,
                 printf(" (async)");
             }
 
-            if ((call->gtFlags & GTF_CALL_UNMANAGED) && (call->gtCallMoreFlags & GTF_CALL_M_FRAME_VAR_DEATH))
-            {
-                printf(" (FramesRoot last use)");
-            }
-
             if ((call->gtFlags & GTF_CALL_INLINE_CANDIDATE) != 0)
             {
                 InlineCandidateInfo* inlineInfo;

src/coreclr/jit/gentree.h

@@ -4356,7 +4356,6 @@ enum GenTreeCallFlags : unsigned int
                                                      // in special cases. Used to optimize fast way out in morphing
     GTF_CALL_M_VIRTSTUB_REL_INDIRECT   = 0x00000020, // the virtstub is indirected through a relative address (only for GTF_CALL_VIRT_STUB)
     GTF_CALL_M_NONVIRT_SAME_THIS       = 0x00000020, // callee "this" pointer is equal to caller this pointer (only for GTF_CALL_NONVIRT)
-    GTF_CALL_M_FRAME_VAR_DEATH         = 0x00000040, // the compLvFrameListRoot variable dies here (last use)
 
     GTF_CALL_M_TAILCALL                = 0x00000080, // the call is a tailcall
     GTF_CALL_M_EXPLICIT_TAILCALL       = 0x00000100, // the call is "tail" prefixed and importer has performed tail call checks

src/coreclr/jit/lclvars.cpp

@@ -3162,22 +3162,6 @@ bool LclVarDsc::CanBeReplacedWithItsField(Compiler* comp) const
 void Compiler::lvaMarkLclRefs(GenTree* tree, BasicBlock* block, Statement* stmt)
 {
     const weight_t weight = block->getBBWeight(this);
-
-    /* Is this a call to unmanaged code ? */
-    if (tree->IsCall() && compMethodRequiresPInvokeFrame())
-    {
-        assert(!opts.ShouldUsePInvokeHelpers() || (info.compLvFrameListRoot == BAD_VAR_NUM));
-        if (!opts.ShouldUsePInvokeHelpers())
-        {
-            /* Get the special variable descriptor */
-            LclVarDsc* varDsc = lvaGetDesc(info.compLvFrameListRoot);
-
-            /* Increment the ref counts twice */
-            varDsc->incRefCnts(weight, this);
-            varDsc->incRefCnts(weight, this);
-        }
-    }
-
     if (tree->OperIs(GT_LCL_ADDR))
     {
         LclVarDsc* varDsc = lvaGetDesc(tree->AsLclVarCommon());

src/coreclr/jit/liveness.cpp

@@ -718,34 +718,6 @@ void Liveness<TLiveness>::PerBlockLocalVarLiveness()
             }
         }
 
-        // Mark the FrameListRoot as used, if applicable.
-
-        if (block->KindIs(BBJ_RETURN) && m_compiler->compMethodRequiresPInvokeFrame())
-        {
-            assert(!m_compiler->opts.ShouldUsePInvokeHelpers() ||
-                   (m_compiler->info.compLvFrameListRoot == BAD_VAR_NUM));
-            if (!m_compiler->opts.ShouldUsePInvokeHelpers())
-            {
-                // 32-bit targets always pop the frame in the epilog.
-                // For 64-bit targets, we only do this in the epilog for IL stubs;
-                // for non-IL stubs the frame is popped after every PInvoke call.
-#ifdef TARGET_64BIT
-                if (m_compiler->opts.jitFlags->IsSet(JitFlags::JIT_FLAG_IL_STUB))
-#endif
-                {
-                    LclVarDsc* varDsc = m_compiler->lvaGetDesc(m_compiler->info.compLvFrameListRoot);
-
-                    if (varDsc->lvTracked)
-                    {
-                        if (!VarSetOps::IsMember(m_compiler, m_curDefSet, varDsc->lvVarIndex))
-                        {
-                            VarSetOps::AddElemD(m_compiler, m_curUseSet, varDsc->lvVarIndex);
-                        }
-                    }
-                }
-            }
-        }
-
         VarSetOps::Assign(m_compiler, block->bbVarUse, m_curUseSet);
         VarSetOps::Assign(m_compiler, block->bbVarDef, m_curDefSet);
 
@@ -933,33 +905,6 @@ void Liveness<TLiveness>::PerNodeLocalVarLiveness(GenTree* tree)
                 }
             }
 
-            // If this is a p/invoke unmanaged call or if this is a tail-call via helper,
-            // and we have an unmanaged p/invoke call in the method,
-            // then we're going to run the p/invoke epilog.
-            // So we mark the FrameRoot as used by this instruction.
-            // This ensures that the block->bbVarUse will contain
-            // the FrameRoot local var if is it a tracked variable.
-
-            if ((call->IsUnmanaged() || call->IsTailCallViaJitHelper()) && m_compiler->compMethodRequiresPInvokeFrame())
-            {
-                assert(!m_compiler->opts.ShouldUsePInvokeHelpers() ||
-                       (m_compiler->info.compLvFrameListRoot == BAD_VAR_NUM));
-                if (!m_compiler->opts.ShouldUsePInvokeHelpers() && !call->IsSuppressGCTransition())
-                {
-                    // Get the FrameRoot local and mark it as used.
-
-                    LclVarDsc* varDsc = m_compiler->lvaGetDesc(m_compiler->info.compLvFrameListRoot);
-
-                    if (varDsc->lvTracked)
-                    {
-                        if (!VarSetOps::IsMember(m_compiler, m_curDefSet, varDsc->lvVarIndex))
-                        {
-                            VarSetOps::AddElemD(m_compiler, m_curUseSet, varDsc->lvVarIndex);
-                        }
-                    }
-                }
-            }
-
             auto visitDef = [=](GenTreeLclVarCommon* lcl) {
                 MarkUseDef(lcl);
                 return GenTree::VisitResult::Continue;
@@ -1767,66 +1712,7 @@ GenTreeLclVarCommon* Liveness<TLiveness>::ComputeLifeCall(VARSET_TP&       life,
                                                           GenTreeCall*     call)
 {
     assert(call != nullptr);
-    // If this is a tail-call via helper, and we have any unmanaged p/invoke calls in
-    // the method, then we're going to run the p/invoke epilog
-    // So we mark the FrameRoot as used by this instruction.
-    // This ensure that this variable is kept alive at the tail-call
-    if (call->IsTailCallViaJitHelper() && m_compiler->compMethodRequiresPInvokeFrame())
-    {
-        assert(!m_compiler->opts.ShouldUsePInvokeHelpers() || (m_compiler->info.compLvFrameListRoot == BAD_VAR_NUM));
-        if (!m_compiler->opts.ShouldUsePInvokeHelpers())
-        {
-            // Get the FrameListRoot local and make it live.
-
-            LclVarDsc* frameVarDsc = m_compiler->lvaGetDesc(m_compiler->info.compLvFrameListRoot);
-
-            if (frameVarDsc->lvTracked)
-            {
-                VarSetOps::AddElemD(m_compiler, life, frameVarDsc->lvVarIndex);
-            }
-        }
-    }
-
-    // TODO: we should generate the code for saving to/restoring
-    //       from the inlined PInvoke frame instead.
-
-    /* Is this call to unmanaged code? */
-    if (call->IsUnmanaged() && m_compiler->compMethodRequiresPInvokeFrame())
-    {
-        // Get the FrameListRoot local and make it live.
-        assert(!m_compiler->opts.ShouldUsePInvokeHelpers() || (m_compiler->info.compLvFrameListRoot == BAD_VAR_NUM));
-        if (!m_compiler->opts.ShouldUsePInvokeHelpers() && !call->IsSuppressGCTransition())
-        {
-            LclVarDsc* frameVarDsc = m_compiler->lvaGetDesc(m_compiler->info.compLvFrameListRoot);
-
-            if (frameVarDsc->lvTracked)
-            {
-                unsigned varIndex = frameVarDsc->lvVarIndex;
-                noway_assert(varIndex < m_compiler->lvaTrackedCount);
-
-                // Is the variable already known to be alive?
-                //
-                if (VarSetOps::IsMember(m_compiler, life, varIndex))
-                {
-                    // Since we may call this multiple times, clear the GTF_CALL_M_FRAME_VAR_DEATH if set.
-                    //
-                    call->gtCallMoreFlags &= ~GTF_CALL_M_FRAME_VAR_DEATH;
-                }
-                else
-                {
-                    // The variable is just coming to life
-                    // Since this is a backwards walk of the trees
-                    // that makes this change in liveness a 'last-use'
-                    //
-                    VarSetOps::AddElemD(m_compiler, life, varIndex);
-                    call->gtCallMoreFlags |= GTF_CALL_M_FRAME_VAR_DEATH;
-                }
-            }
-        }
-    }
-
     GenTreeLclVarCommon* partialDef = nullptr;
-
     auto visitDef = [&](const LocalDef& def) {
         if (!def.IsEntire)
         {
@@ -2371,16 +2257,6 @@ void Liveness<TLiveness>::ComputeLifeLIR(VARSET_TP& life, BasicBlock* block, VAR
                     });
 
                     blockRange.Remove(node);
-
-                    // Removing a call does not affect liveness unless it is a tail call in a method with P/Invokes or
-                    // is itself a P/Invoke, in which case it may affect the liveness of the frame root variable.
-                    if (!m_compiler->opts.ShouldUsePInvokeHelpers() &&
-                        ((call->IsTailCall() && m_compiler->compMethodRequiresPInvokeFrame()) ||
-                         (call->IsUnmanaged() && !call->IsSuppressGCTransition())) &&
-                        m_compiler->lvaTable[m_compiler->info.compLvFrameListRoot].lvTracked)
-                    {
-                        m_compiler->fgStmtRemoved = true;
-                    }
                 }
                 else
                 {