Be careful with predecessor/successor index.

When we simplify the CFG, we must preserve things that were already
simplified. For example, the index in the predecessor list or
successor list of a block must be preserved for ensuring the
first block is a loop pre header.

bug:21867463

(cherry picked from commit 8b20f88b0a8d1b374dd5eaae289d19734c77b8f8)

Change-Id: I2581b5a50942290da96cd9ec876f6f2573e0a6c4

5 files changed, 29 insertions, 14 deletions

diff --git a/compiler/optimizing/constant_folding_test.cc b/compiler/optimizing/constant_folding_test.cc
index 422223f..11f6362 100644
--- a/compiler/optimizing/constant_folding_test.cc
+++ b/compiler/optimizing/constant_folding_test.cc
@@ -627,8 +627,8 @@ TEST(ConstantFolding, ConstantCondition) {
     "  9: If(8)\n"
     "BasicBlock 2, pred: 1, succ: 3\n"
     "  12: Goto 3\n"
-    "BasicBlock 3, pred: 2, 5, succ: 4\n"
-    "  22: Phi(3, 5) [15]\n"
+    "BasicBlock 3, pred: 5, 2, succ: 4\n"
+    "  22: Phi(5, 3) [15]\n"
     "  15: Add(22, 3)\n"
     "  17: ReturnVoid\n"
     "BasicBlock 4, pred: 3\n"
diff --git a/compiler/optimizing/dead_code_elimination_test.cc b/compiler/optimizing/dead_code_elimination_test.cc
index 3209d3e..ee3a61a 100644
--- a/compiler/optimizing/dead_code_elimination_test.cc
+++ b/compiler/optimizing/dead_code_elimination_test.cc
@@ -89,8 +89,8 @@ TEST(DeadCodeElimination, AdditionAndConditionalJump) {
     "  9: If(8)\n"
     "BasicBlock 2, pred: 1, succ: 3\n"
     "  12: Goto 3\n"
-    "BasicBlock 3, pred: 2, 5, succ: 4\n"
-    "  22: Phi(3, 5) [15]\n"
+    "BasicBlock 3, pred: 5, 2, succ: 4\n"
+    "  22: Phi(5, 3) [15]\n"
     "  15: Add(22, 3)\n"
     "  17: ReturnVoid\n"
     "BasicBlock 4, pred: 3\n"
@@ -101,7 +101,7 @@ TEST(DeadCodeElimination, AdditionAndConditionalJump) {
   // Expected difference after dead code elimination.
   diff_t expected_diff = {
     { "  3: IntConstant [15, 22, 8]\n", "  3: IntConstant [22, 8]\n" },
-    { "  22: Phi(3, 5) [15]\n",         "  22: Phi(3, 5)\n" },
+    { "  22: Phi(5, 3) [15]\n",         "  22: Phi(5, 3)\n" },
     { "  15: Add(22, 3)\n",             removed }
   };
   std::string expected_after = Patch(expected_before, expected_diff);
diff --git a/compiler/optimizing/nodes.cc b/compiler/optimizing/nodes.cc
index fb150c3..c01364a 100644
--- a/compiler/optimizing/nodes.cc
+++ b/compiler/optimizing/nodes.cc
@@ -179,8 +179,9 @@ void HGraph::SplitCriticalEdge(HBasicBlock* block, HBasicBlock* successor) {
   HBasicBlock* new_block = new (arena_) HBasicBlock(this, successor->GetDexPc());
   AddBlock(new_block);
   new_block->AddInstruction(new (arena_) HGoto());
-  block->ReplaceSuccessor(successor, new_block);
-  new_block->AddSuccessor(successor);
+  // Use `InsertBetween` to ensure the predecessor index and successor index of
+  // `block` and `successor` are preserved.
+  new_block->InsertBetween(block, successor);
   if (successor->IsLoopHeader()) {
     // If we split at a back edge boundary, make the new block the back edge.
     HLoopInformation* info = successor->GetLoopInformation();
diff --git a/compiler/optimizing/nodes.h b/compiler/optimizing/nodes.h
index c1f1c9d..394e3fc 100644
--- a/compiler/optimizing/nodes.h
+++ b/compiler/optimizing/nodes.h
@@ -582,6 +582,20 @@ class HBasicBlock : public ArenaObject<kArenaAllocMisc> {
     predecessors_.Put(predecessor_index, new_block);
   }
 
+  // Insert `this` between `predecessor` and `successor. This method
+  // preserves the indicies, and will update the first edge found between
+  // `predecessor` and `successor`.
+  void InsertBetween(HBasicBlock* predecessor, HBasicBlock* successor) {
+    size_t predecessor_index = successor->GetPredecessorIndexOf(predecessor);
+    DCHECK_NE(predecessor_index, static_cast<size_t>(-1));
+    size_t successor_index = predecessor->GetSuccessorIndexOf(successor);
+    DCHECK_NE(successor_index, static_cast<size_t>(-1));
+    successor->predecessors_.Put(predecessor_index, this);
+    predecessor->successors_.Put(successor_index, this);
+    successors_.Add(successor);
+    predecessors_.Add(predecessor);
+  }
+
   void RemovePredecessor(HBasicBlock* block) {
     predecessors_.Delete(block);
   }
diff --git a/compiler/optimizing/ssa_test.cc b/compiler/optimizing/ssa_test.cc
index fb3e7d7..0e8c058 100644
--- a/compiler/optimizing/ssa_test.cc
+++ b/compiler/optimizing/ssa_test.cc
@@ -115,7 +115,7 @@ TEST(SsaTest, CFG1) {
     "  3: If(2)\n"
     "BasicBlock 2, pred: 1, succ: 3\n"
     "  4: Goto\n"
-    "BasicBlock 3, pred: 2, 5, succ: 4\n"
+    "BasicBlock 3, pred: 5, 2, succ: 4\n"
     "  5: ReturnVoid\n"
     "BasicBlock 4, pred: 3\n"
     "  6: Exit\n"
@@ -145,8 +145,8 @@ TEST(SsaTest, CFG2) {
     "  4: If(3)\n"
     "BasicBlock 2, pred: 1, succ: 3\n"
     "  5: Goto\n"
-    "BasicBlock 3, pred: 2, 5, succ: 4\n"
-    "  6: Phi(1, 0) [7]\n"
+    "BasicBlock 3, pred: 5, 2, succ: 4\n"
+    "  6: Phi(0, 1) [7]\n"
     "  7: Return(6)\n"
     "BasicBlock 4, pred: 3\n"
     "  8: Exit\n"
@@ -428,8 +428,8 @@ TEST(SsaTest, Loop7) {
     "  10: Goto\n"
     "BasicBlock 5, pred: 3, succ: 2\n"
     "  11: Goto\n"
-    "BasicBlock 6, pred: 4, 8, succ: 7\n"
-    "  12: Phi(2, 5) [13]\n"
+    "BasicBlock 6, pred: 8, 4, succ: 7\n"
+    "  12: Phi(5, 2) [13]\n"
     "  13: Return(12)\n"
     "BasicBlock 7, pred: 6\n"
     "  14: Exit\n"
@@ -480,7 +480,7 @@ TEST(SsaTest, LocalInIf) {
     "  4: If(3)\n"
     "BasicBlock 2, pred: 1, succ: 3\n"
     "  5: Goto\n"
-    "BasicBlock 3, pred: 2, 5, succ: 4\n"
+    "BasicBlock 3, pred: 5, 2, succ: 4\n"
     "  6: ReturnVoid\n"
     "BasicBlock 4, pred: 3\n"
     "  7: Exit\n"
@@ -517,7 +517,7 @@ TEST(SsaTest, MultiplePredecessors) {
     "  8: Add(0, 0)\n"
     "  9: Goto\n"
     // This block should not get a phi for local 1.
-    "BasicBlock 5, pred: 2, 4, 7, succ: 6\n"
+    "BasicBlock 5, pred: 2, 7, 4, succ: 6\n"
     "  10: ReturnVoid\n"
     "BasicBlock 6, pred: 5\n"
     "  11: Exit\n"