From 1536b67b3a5746e1174c0760b16db85f882c2085 Mon Sep 17 00:00:00 2001
From: Jakob Botsch Nielsen <jakob.botsch.nielsen@gmail.com>
Date: Fri, 17 Jun 2022 15:20:42 +0200
Subject: [PATCH] Allow more permissive forward subbing into call arguments

---
 src/coreclr/jit/forwardsub.cpp | 41 +---------------------------------
 1 file changed, 1 insertion(+), 40 deletions(-)

diff --git a/src/coreclr/jit/forwardsub.cpp b/src/coreclr/jit/forwardsub.cpp
index 4c3fae5f1d9f9..a05ef79fd572f 100644
--- a/src/coreclr/jit/forwardsub.cpp
+++ b/src/coreclr/jit/forwardsub.cpp
@@ -187,7 +187,6 @@ class ForwardSubVisitor final : public GenTreeVisitor<ForwardSubVisitor>
 public:
     enum
     {
-        ComputeStack      = true,
         DoPostOrder       = true,
         UseExecutionOrder = true
     };
@@ -197,7 +196,6 @@ class ForwardSubVisitor final : public GenTreeVisitor<ForwardSubVisitor>
         , m_use(nullptr)
         , m_node(nullptr)
         , m_parentNode(nullptr)
-        , m_callAncestor(nullptr)
         , m_lclNum(lclNum)
         , m_useCount(0)
         , m_useFlags(GTF_EMPTY)
@@ -221,7 +219,7 @@ class ForwardSubVisitor final : public GenTreeVisitor<ForwardSubVisitor>
 
                 // Screen out contextual "uses"
                 //
-                GenTree* const parent = m_ancestors.Top(1);
+                GenTree* const parent = user;
                 bool const     isDef  = parent->OperIs(GT_ASG) && (parent->gtGetOp1() == node);
                 bool const     isAddr = parent->OperIs(GT_ADDR);
 
@@ -243,19 +241,6 @@ class ForwardSubVisitor final : public GenTreeVisitor<ForwardSubVisitor>
                     m_use        = use;
                     m_useFlags   = m_accumulatedFlags;
                     m_parentNode = parent;
-
-                    // If this use contributes to a call arg we need to
-                    // remember the call and handle it specially when we
-                    // see it later in the postorder walk.
-                    //
-                    for (int i = 1; i < m_ancestors.Height(); i++)
-                    {
-                        if (m_ancestors.Top(i)->IsCall())
-                        {
-                            m_callAncestor = m_ancestors.Top(i)->AsCall();
-                            break;
-                        }
-                    }
                 }
             }
         }
@@ -274,29 +259,6 @@ class ForwardSubVisitor final : public GenTreeVisitor<ForwardSubVisitor>
             }
         }
 
-        // Is this the use's call ancestor?
-        //
-        if ((m_callAncestor != nullptr) && (node == m_callAncestor))
-        {
-            // To be conservative and avoid issues with morph
-            // reordering call args, we merge in effects of all args
-            // to this call.
-            //
-            // Remove this if/when morph's arg sorting is fixed.
-            //
-            GenTreeFlags oldUseFlags = m_useFlags;
-
-            for (CallArg& arg : m_callAncestor->gtArgs.Args())
-            {
-                m_useFlags |= (arg.GetNode()->gtFlags & GTF_GLOB_EFFECT);
-            }
-
-            if (oldUseFlags != m_useFlags)
-            {
-                JITDUMP(" [added other call arg use flags: 0x%x]", m_useFlags & ~oldUseFlags);
-            }
-        }
-
         m_accumulatedFlags |= (node->gtFlags & GTF_GLOB_EFFECT);
 
         return fgWalkResult::WALK_CONTINUE;
@@ -341,7 +303,6 @@ class ForwardSubVisitor final : public GenTreeVisitor<ForwardSubVisitor>
     GenTree**    m_use;
     GenTree*     m_node;
     GenTree*     m_parentNode;
-    GenTreeCall* m_callAncestor;
     unsigned     m_lclNum;
     unsigned     m_useCount;
     GenTreeFlags m_useFlags;