From f7a90a380f06287c17a57f391b68df7152de8b0e Mon Sep 17 00:00:00 2001
From: Sergey Andreenko <seandree@microsoft.com>
Date: Mon, 22 Jun 2020 03:20:59 -0700
Subject: [PATCH] Add SSA support.

---
 src/coreclr/src/jit/morph.cpp      |  3 ---
 src/coreclr/src/jit/rangecheck.cpp | 22 +++++++++++++++++++---
 src/coreclr/src/jit/ssabuilder.cpp | 14 +++++++++++---
 src/coreclr/src/jit/valuenum.cpp   |  6 ++++++
 4 files changed, 36 insertions(+), 9 deletions(-)

diff --git a/src/coreclr/src/jit/morph.cpp b/src/coreclr/src/jit/morph.cpp
index 00c548c288423..b67531a101fa5 100644
--- a/src/coreclr/src/jit/morph.cpp
+++ b/src/coreclr/src/jit/morph.cpp
@@ -10342,9 +10342,6 @@ GenTree* Compiler::fgMorphCopyBlock(GenTree* tree)
         if (varTypeIsStruct(varDsc) && varDsc->CanBeReplacedWithItsField(this))
         {
             JITDUMP(" not morphing a single reg call return\n");
-            // Set `lvIsMultiRegRet` to exclude it from SSA, it is a temporary solution,
-            // inspired by multi-reg call work. We should support SSA for such structs in the future.
-            varDsc->lvIsMultiRegRet = true;
             return tree;
         }
     }
diff --git a/src/coreclr/src/jit/rangecheck.cpp b/src/coreclr/src/jit/rangecheck.cpp
index 9fb0eaf0357d2..663c3a1537d34 100644
--- a/src/coreclr/src/jit/rangecheck.cpp
+++ b/src/coreclr/src/jit/rangecheck.cpp
@@ -444,7 +444,12 @@ LclSsaVarDsc* RangeCheck::GetSsaDefAsg(GenTreeLclVarCommon* lclUse)
         return nullptr;
     }
 
-    LclSsaVarDsc* ssaDef = m_pCompiler->lvaGetDesc(lclUse)->GetPerSsaData(ssaNum);
+    LclVarDsc* varDsc = m_pCompiler->lvaGetDesc(lclUse);
+    if (varDsc->CanBeReplacedWithItsField(m_pCompiler))
+    {
+        varDsc = m_pCompiler->lvaGetDesc(varDsc->lvFieldLclStart);
+    }
+    LclSsaVarDsc* ssaDef = varDsc->GetPerSsaData(ssaNum);
 
     // RangeCheck does not care about uninitialized variables.
     if (ssaDef->GetAssignment() == nullptr)
@@ -472,6 +477,11 @@ LclSsaVarDsc* RangeCheck::GetSsaDefAsg(GenTreeLclVarCommon* lclUse)
 #ifdef DEBUG
 UINT64 RangeCheck::HashCode(unsigned lclNum, unsigned ssaNum)
 {
+    LclVarDsc* varDsc = m_pCompiler->lvaGetDesc(lclNum);
+    if (varDsc->CanBeReplacedWithItsField(m_pCompiler))
+    {
+        lclNum = varDsc->lvFieldLclStart;
+    }
     assert(ssaNum != SsaConfig::RESERVED_SSA_NUM);
     return UINT64(lclNum) << 32 | ssaNum;
 }
@@ -499,7 +509,8 @@ RangeCheck::Location* RangeCheck::GetDef(unsigned lclNum, unsigned ssaNum)
 
 RangeCheck::Location* RangeCheck::GetDef(GenTreeLclVarCommon* lcl)
 {
-    return GetDef(lcl->GetLclNum(), lcl->GetSsaNum());
+    unsigned lclNum = lcl->GetLclNum();
+    return GetDef(lclNum, lcl->GetSsaNum());
 }
 
 // Add the def location to the hash table.
@@ -546,7 +557,12 @@ void RangeCheck::MergeEdgeAssertions(GenTreeLclVarCommon* lcl, ASSERT_VALARG_TP
         Limit      limit(Limit::keUndef);
         genTreeOps cmpOper = GT_NONE;
 
-        LclSsaVarDsc* ssaData     = m_pCompiler->lvaTable[lcl->GetLclNum()].GetPerSsaData(lcl->GetSsaNum());
+        LclVarDsc* varDsc = m_pCompiler->lvaGetDesc(lcl);
+        if (varDsc->CanBeReplacedWithItsField(m_pCompiler))
+        {
+            varDsc = m_pCompiler->lvaGetDesc(varDsc->lvFieldLclStart);
+        }
+        LclSsaVarDsc* ssaData     = varDsc->GetPerSsaData(lcl->GetSsaNum());
         ValueNum      normalLclVN = m_pCompiler->vnStore->VNConservativeNormalValue(ssaData->m_vnPair);
 
         // Current assertion is of the form (i < len - cns) != 0
diff --git a/src/coreclr/src/jit/ssabuilder.cpp b/src/coreclr/src/jit/ssabuilder.cpp
index 3bd0b44c4f2b4..5a1df78f21e59 100644
--- a/src/coreclr/src/jit/ssabuilder.cpp
+++ b/src/coreclr/src/jit/ssabuilder.cpp
@@ -749,7 +749,15 @@ void SsaBuilder::RenameDef(GenTreeOp* asgNode, BasicBlock* block)
 
     if (isLocal)
     {
-        unsigned lclNum = lclNode->GetLclNum();
+        unsigned   lclNum = lclNode->GetLclNum();
+        LclVarDsc* varDsc = m_pCompiler->lvaGetDesc(lclNum);
+
+        if (!m_pCompiler->lvaInSsa(lclNum) && varDsc->CanBeReplacedWithItsField(m_pCompiler))
+        {
+            lclNum = varDsc->lvFieldLclStart;
+            varDsc = m_pCompiler->lvaGetDesc(lclNum);
+            assert(isFullDef);
+        }
 
         if (m_pCompiler->lvaInSsa(lclNum))
         {
@@ -758,7 +766,7 @@ void SsaBuilder::RenameDef(GenTreeOp* asgNode, BasicBlock* block)
             // This should have been marked as defintion.
             assert((lclNode->gtFlags & GTF_VAR_DEF) != 0);
 
-            unsigned ssaNum = m_pCompiler->lvaGetDesc(lclNum)->lvPerSsaData.AllocSsaNum(m_allocator, block, asgNode);
+            unsigned ssaNum = varDsc->lvPerSsaData.AllocSsaNum(m_allocator, block, asgNode);
 
             if (!isFullDef)
             {
@@ -787,7 +795,7 @@ void SsaBuilder::RenameDef(GenTreeOp* asgNode, BasicBlock* block)
             }
 
             // If it's a SSA local then it cannot be address exposed and thus does not define SSA memory.
-            assert(!m_pCompiler->lvaVarAddrExposed(lclNode->GetLclNum()));
+            assert(!m_pCompiler->lvaVarAddrExposed(lclNum));
             return;
         }
 
diff --git a/src/coreclr/src/jit/valuenum.cpp b/src/coreclr/src/jit/valuenum.cpp
index 2fb9c3ce14e46..2e65f36aa163b 100644
--- a/src/coreclr/src/jit/valuenum.cpp
+++ b/src/coreclr/src/jit/valuenum.cpp
@@ -6859,6 +6859,12 @@ void Compiler::fgValueNumberTree(GenTree* tree)
                 unsigned             lclNum = lcl->GetLclNum();
                 LclVarDsc*           varDsc = &lvaTable[lclNum];
 
+                if (varDsc->CanBeReplacedWithItsField(this))
+                {
+                    lclNum = varDsc->lvFieldLclStart;
+                    varDsc = &lvaTable[lclNum];
+                }
+
                 // Do we have a Use (read) of the LclVar?
                 //
                 if ((lcl->gtFlags & GTF_VAR_DEF) == 0 ||