From b143274ad0b51709eb7840881eb9857330731fba Mon Sep 17 00:00:00 2001
From: Chandler Carruth <chandlerc@gmail.com>
Date: Mon, 28 Jul 2014 17:55:07 +0000
Subject: [PATCH] [SDAG] Add DEBUG logging to the legalizer, fixing a "bug"
 found by inspection in the proccess, and shuffle the logging in the DAG
 combiner around a bit.

With this it is much easier to follow what the legalizer is doing. It
should even accurately present most of the strange legalization
operations where a single node is replaced by multiple nodes, etc. There
is still some information lost (we log SDNodes not SDValues so we don't
log which result is used for which thing), but I think this is much
closer to a usable system. Notably, this will make it *much* more
apparant when legalization is actually happening inside the combiner, or
when there is a cycle caused by interactions of the legalizer and the
combiner.

The "bug" I fixed here I'm not sure is remotely possible to trigger. We
were only adding one of the nodes in a replacement to the updated set
rather than all of the nodes in the replacement. Realistically, the
worst result of this are nodes not getting back onto the worklist in the
DAG combiner. I doubt it is possible to trigger this today, and
I certainly don't have any ideas about how, but this at least brings the
code into alignment with the principled operation of the routine.

llvm-svn: 214105
---
 llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp |  5 ++---
 llvm/lib/CodeGen/SelectionDAG/LegalizeDAG.cpp | 22 +++++++++++++++++++---
 2 files changed, 21 insertions(+), 6 deletions(-)

diff --git a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
index 8b1854e..5fb0ea9 100644
--- a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -1156,9 +1156,6 @@ void DAGCombiner::Run(CombineLevel AtLevel) {
     if (recursivelyDeleteUnusedNodes(N))
       continue;
 
-    DEBUG(dbgs() << "\nCombining: ";
-          N->dump(&DAG));
-
     // Add any operands of the new node which have not yet been combined to the
     // worklist as well. Because the worklist uniques things already, this
     // won't repeatedly process the same operand.
@@ -1183,6 +1180,8 @@ void DAGCombiner::Run(CombineLevel AtLevel) {
         continue;
     }
 
+    DEBUG(dbgs() << "\nCombining: "; N->dump(&DAG));
+
     SDValue RV = combine(N);
 
     if (!RV.getNode())
diff --git a/llvm/lib/CodeGen/SelectionDAG/LegalizeDAG.cpp b/llvm/lib/CodeGen/SelectionDAG/LegalizeDAG.cpp
index c36e175..6a3402a 100644
--- a/llvm/lib/CodeGen/SelectionDAG/LegalizeDAG.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/LegalizeDAG.cpp
@@ -36,6 +36,8 @@
 #include "llvm/Target/TargetMachine.h"
 using namespace llvm;
 
+#define DEBUG_TYPE "legalizedag"
+
 //===----------------------------------------------------------------------===//
 /// SelectionDAGLegalize - This takes an arbitrary SelectionDAG as input and
 /// hacks on it until the target machine can handle it.  This involves
@@ -180,6 +182,9 @@ public:
     }
   }
   void ReplaceNode(SDNode *Old, SDNode *New) {
+    DEBUG(dbgs() << " ... replacing: "; Old->dump(&DAG);
+          dbgs() << "     with:      "; New->dump(&DAG));
+
     assert(Old->getNumValues() == New->getNumValues() &&
            "Replacing one node with another that produces a different number "
            "of values!");
@@ -191,6 +196,9 @@ public:
     ReplacedNode(Old);
   }
   void ReplaceNode(SDValue Old, SDValue New) {
+    DEBUG(dbgs() << " ... replacing: "; Old->dump(&DAG);
+          dbgs() << "     with:      "; New->dump(&DAG));
+
     DAG.ReplaceAllUsesWith(Old, New);
     DAG.TransferDbgValues(Old, New);
     if (UpdatedNodes)
@@ -198,11 +206,17 @@ public:
     ReplacedNode(Old.getNode());
   }
   void ReplaceNode(SDNode *Old, const SDValue *New) {
+    DEBUG(dbgs() << " ... replacing: "; Old->dump(&DAG));
+
     DAG.ReplaceAllUsesWith(Old, New);
-    for (unsigned i = 0, e = Old->getNumValues(); i != e; ++i)
+    for (unsigned i = 0, e = Old->getNumValues(); i != e; ++i) {
+      DEBUG(dbgs() << (i == 0 ? "     with:      "
+                              : "      and:      ");
+            New[i]->dump(&DAG));
       DAG.TransferDbgValues(SDValue(Old, i), New[i]);
-    if (UpdatedNodes)
-      UpdatedNodes->insert(New->getNode());
+      if (UpdatedNodes)
+        UpdatedNodes->insert(New[i].getNode());
+    }
     ReplacedNode(Old);
   }
 };
@@ -1160,6 +1174,8 @@ void SelectionDAGLegalize::LegalizeLoadOps(SDNode *Node) {
 /// LegalizeOp - Return a legal replacement for the given operation, with
 /// all legal operands.
 void SelectionDAGLegalize::LegalizeOp(SDNode *Node) {
+  DEBUG(dbgs() << "\nLegalizing: "; Node->dump(&DAG));
+
   if (Node->getOpcode() == ISD::TargetConstant) // Allow illegal target nodes.
     return;
 
-- 
2.7.4