Merge "ART: Try to statically evaluate some conditions."

3 files changed, 44 insertions, 7 deletions

diff --git a/compiler/optimizing/instruction_simplifier.cc b/compiler/optimizing/instruction_simplifier.cc
index a42a85dc1d..53e449bbbe 100644
--- a/compiler/optimizing/instruction_simplifier.cc
+++ b/compiler/optimizing/instruction_simplifier.cc
@@ -994,6 +994,27 @@ void InstructionSimplifierVisitor::VisitIf(HIf* instruction) {
     instruction->GetBlock()->SwapSuccessors();
     RecordSimplification();
   }
+  HInstruction* input = instruction->InputAt(0);
+
+  // If a condition 'cond' is evaluated in an HIf instruction then in the successors of the
+  // IF_BLOCK we statically know the value of the condition (TRUE in TRUE_SUCC, FALSE in
+  // FALSE_SUCC). Using that we can replace another evaluation (use) EVAL of the same 'cond'
+  // with TRUE value (FALSE value) if every path from the ENTRY_BLOCK to EVAL_BLOCK contains the
+  // edge HIF_BLOCK->TRUE_SUCC (HIF_BLOCK->FALSE_SUCC).
+  if (!input->IsConstant()) {
+    HBasicBlock* true_succ = instruction->IfTrueSuccessor();
+    HBasicBlock* false_succ = instruction->IfFalseSuccessor();
+
+    DCHECK_EQ(true_succ->GetPredecessors().size(), 1u);
+    input->ReplaceUsesDominatedBy(
+        true_succ->GetFirstInstruction(), GetGraph()->GetIntConstant(1), /* strictly */ false);
+    RecordSimplification();
+
+    DCHECK_EQ(false_succ->GetPredecessors().size(), 1u);
+    input->ReplaceUsesDominatedBy(
+        false_succ->GetFirstInstruction(), GetGraph()->GetIntConstant(0), /* strictly */ false);
+    RecordSimplification();
+  }
 }
 
 void InstructionSimplifierVisitor::VisitArrayLength(HArrayLength* instruction) {
diff --git a/compiler/optimizing/nodes.cc b/compiler/optimizing/nodes.cc
index 5f33ed6303..d39c2aded5 100644
--- a/compiler/optimizing/nodes.cc
+++ b/compiler/optimizing/nodes.cc
@@ -1111,10 +1111,10 @@ bool HInstructionList::FoundBefore(const HInstruction* instruction1,
   return true;
 }
 
-bool HInstruction::StrictlyDominates(HInstruction* other_instruction) const {
+bool HInstruction::Dominates(HInstruction* other_instruction, bool strictly) const {
   if (other_instruction == this) {
     // An instruction does not strictly dominate itself.
-    return false;
+    return !strictly;
   }
   HBasicBlock* block = GetBlock();
   HBasicBlock* other_block = other_instruction->GetBlock();
@@ -1148,6 +1148,10 @@ bool HInstruction::StrictlyDominates(HInstruction* other_instruction) const {
   }
 }
 
+bool HInstruction::StrictlyDominates(HInstruction* other_instruction) const {
+  return Dominates(other_instruction, /* strictly */ true);
+}
+
 void HInstruction::RemoveEnvironment() {
   RemoveEnvironmentUses(this);
   environment_ = nullptr;
@@ -1170,14 +1174,16 @@ void HInstruction::ReplaceWith(HInstruction* other) {
   DCHECK(env_uses_.empty());
 }
 
-void HInstruction::ReplaceUsesDominatedBy(HInstruction* dominator, HInstruction* replacement) {
+void HInstruction::ReplaceUsesDominatedBy(HInstruction* dominator,
+                                          HInstruction* replacement,
+                                          bool strictly) {
   const HUseList<HInstruction*>& uses = GetUses();
   for (auto it = uses.begin(), end = uses.end(); it != end; /* ++it below */) {
     HInstruction* user = it->GetUser();
     size_t index = it->GetIndex();
     // Increment `it` now because `*it` may disappear thanks to user->ReplaceInput().
     ++it;
-    if (dominator->StrictlyDominates(user)) {
+    if (dominator->Dominates(user, strictly)) {
       user->ReplaceInput(replacement, index);
     }
   }
diff --git a/compiler/optimizing/nodes.h b/compiler/optimizing/nodes.h
index 42a9d95b9a..affd54ed72 100644
--- a/compiler/optimizing/nodes.h
+++ b/compiler/optimizing/nodes.h
@@ -2098,9 +2098,13 @@ class HInstruction : public ArenaObject<kArenaAllocInstruction> {
     return IsRemovable() && !HasUses();
   }
 
-  // Does this instruction strictly dominate `other_instruction`?
-  // Returns false if this instruction and `other_instruction` are the same.
+  // Does this instruction dominate (strictly or in regular sense depending on 'strictly')
+  // `other_instruction`?
+  // Returns '!strictly' if this instruction and `other_instruction` are the same.
   // Aborts if this instruction and `other_instruction` are both phis.
+  bool Dominates(HInstruction* other_instruction, bool strictly) const;
+
+  // Return 'Dominates(other_instruction, /*strictly*/ true)'.
   bool StrictlyDominates(HInstruction* other_instruction) const;
 
   int GetId() const { return id_; }
@@ -2161,7 +2165,13 @@ class HInstruction : public ArenaObject<kArenaAllocInstruction> {
   void SetLocations(LocationSummary* locations) { locations_ = locations; }
 
   void ReplaceWith(HInstruction* instruction);
-  void ReplaceUsesDominatedBy(HInstruction* dominator, HInstruction* replacement);
+
+  // Replace all uses of the instruction which are dominated by 'dominator' with 'replacement'.
+  // 'strictly' determines whether strict or regular domination relation should be checked.
+  void ReplaceUsesDominatedBy(HInstruction* dominator,
+                              HInstruction* replacement,
+                              bool strictly = true);
+
   void ReplaceInput(HInstruction* replacement, size_t index);
 
   // This is almost the same as doing `ReplaceWith()`. But in this helper, the