[DAG] Don't map a TableId to itself in the ReplacedValues map

Summary:
Found some regressions (infinite loop in DAGTypeLegalizer::RemapId)
after r334880. This patch makes sure that we do map a TableId to
itself.

Reviewers: niravd

Reviewed By: niravd

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D48364

llvm-svn: 335141

2 files changed, 7 insertions, 3 deletions

diff --git a/llvm/lib/CodeGen/SelectionDAG/LegalizeTypes.cpp b/llvm/lib/CodeGen/SelectionDAG/LegalizeTypes.cpp
index 77e167dfb08..a9f144c06e9 100644
--- a/llvm/lib/CodeGen/SelectionDAG/LegalizeTypes.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/LegalizeTypes.cpp
@@ -575,6 +575,7 @@ void DAGTypeLegalizer::RemapValue(SDValue &V) {
 void DAGTypeLegalizer::RemapId(TableId &Id) {
   auto I = ReplacedValues.find(Id);
   if (I != ReplacedValues.end()) {
+    assert(Id != I->second && "Id is mapped to itself.");
     // Use path compression to speed up future lookups if values get multiply
     // replaced with other values.
     RemapId(I->second);
@@ -652,7 +653,8 @@ void DAGTypeLegalizer::ReplaceValueWith(SDValue From, SDValue To) {
     auto FromId = getTableId(From);
     auto ToId = getTableId(To);
 
-    ReplacedValues[FromId] = ToId;
+    if (FromId != ToId)
+      ReplacedValues[FromId] = ToId;
     DAG.ReplaceAllUsesOfValueWith(From, To);
 
     // Process the list of nodes that need to be reanalyzed.
@@ -685,7 +687,8 @@ void DAGTypeLegalizer::ReplaceValueWith(SDValue From, SDValue To) {
           auto OldValId = getTableId(OldVal);
           auto NewValId = getTableId(NewVal);
           DAG.ReplaceAllUsesOfValueWith(OldVal, NewVal);
-          ReplacedValues[OldValId] = NewValId;
+          if (OldValId != NewValId)
+            ReplacedValues[OldValId] = NewValId;
         }
         // The original node continues to exist in the DAG, marked NewNode.
       }
diff --git a/llvm/lib/CodeGen/SelectionDAG/LegalizeTypes.h b/llvm/lib/CodeGen/SelectionDAG/LegalizeTypes.h
index 6d577adc6f4..e4d4aac3340 100644
--- a/llvm/lib/CodeGen/SelectionDAG/LegalizeTypes.h
+++ b/llvm/lib/CodeGen/SelectionDAG/LegalizeTypes.h
@@ -186,7 +186,8 @@ public:
       TableId NewId = getTableId(SDValue(New, i));
       TableId OldId = getTableId(SDValue(Old, i));
 
-      ReplacedValues[OldId] = NewId;
+      if (OldId != NewId)
+        ReplacedValues[OldId] = NewId;
 
       // Delete Node from tables.
       ValueToIdMap.erase(SDValue(Old, i));