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-rw-r--r--compiler/optimizing/constant_folding.cc124
-rw-r--r--compiler/optimizing/constant_folding.h7
-rw-r--r--compiler/optimizing/instruction_simplifier.h7
3 files changed, 91 insertions, 47 deletions
diff --git a/compiler/optimizing/constant_folding.cc b/compiler/optimizing/constant_folding.cc
index 014353d615..7ddabdee78 100644
--- a/compiler/optimizing/constant_folding.cc
+++ b/compiler/optimizing/constant_folding.cc
@@ -18,8 +18,28 @@
namespace art {
-// This visitor tries to simplify operations that yield a constant. For example
-// `input * 0` is replaced by a null constant.
+// This visitor tries to simplify instructions that can be evaluated
+// as constants.
+class HConstantFoldingVisitor : public HGraphDelegateVisitor {
+ public:
+ explicit HConstantFoldingVisitor(HGraph* graph)
+ : HGraphDelegateVisitor(graph) {}
+
+ private:
+ void VisitBasicBlock(HBasicBlock* block) OVERRIDE;
+
+ void VisitUnaryOperation(HUnaryOperation* inst) OVERRIDE;
+ void VisitBinaryOperation(HBinaryOperation* inst) OVERRIDE;
+
+ void VisitTypeConversion(HTypeConversion* inst) OVERRIDE;
+ void VisitDivZeroCheck(HDivZeroCheck* inst) OVERRIDE;
+
+ DISALLOW_COPY_AND_ASSIGN(HConstantFoldingVisitor);
+};
+
+// This visitor tries to simplify operations with an absorbing input,
+// yielding a constant. For example `input * 0` is replaced by a
+// null constant.
class InstructionWithAbsorbingInputSimplifier : public HGraphVisitor {
public:
explicit InstructionWithAbsorbingInputSimplifier(HGraph* graph) : HGraphVisitor(graph) {}
@@ -44,59 +64,69 @@ class InstructionWithAbsorbingInputSimplifier : public HGraphVisitor {
void VisitXor(HXor* instruction) OVERRIDE;
};
+
void HConstantFolding::Run() {
- InstructionWithAbsorbingInputSimplifier simplifier(graph_);
+ HConstantFoldingVisitor visitor(graph_);
// Process basic blocks in reverse post-order in the dominator tree,
// so that an instruction turned into a constant, used as input of
// another instruction, may possibly be used to turn that second
// instruction into a constant as well.
- for (HReversePostOrderIterator it(*graph_); !it.Done(); it.Advance()) {
- HBasicBlock* block = it.Current();
- // Traverse this block's instructions in (forward) order and
- // replace the ones that can be statically evaluated by a
- // compile-time counterpart.
- for (HInstructionIterator inst_it(block->GetInstructions());
- !inst_it.Done(); inst_it.Advance()) {
- HInstruction* inst = inst_it.Current();
- if (inst->IsBinaryOperation()) {
- // Constant folding: replace `op(a, b)' with a constant at
- // compile time if `a' and `b' are both constants.
- HConstant* constant = inst->AsBinaryOperation()->TryStaticEvaluation();
- if (constant != nullptr) {
- inst->ReplaceWith(constant);
- inst->GetBlock()->RemoveInstruction(inst);
- } else {
- inst->Accept(&simplifier);
- }
- } else if (inst->IsUnaryOperation()) {
- // Constant folding: replace `op(a)' with a constant at compile
- // time if `a' is a constant.
- HConstant* constant = inst->AsUnaryOperation()->TryStaticEvaluation();
- if (constant != nullptr) {
- inst->ReplaceWith(constant);
- inst->GetBlock()->RemoveInstruction(inst);
- }
- } else if (inst->IsTypeConversion()) {
- // Constant folding: replace `TypeConversion(a)' with a constant at
- // compile time if `a' is a constant.
- HConstant* constant = inst->AsTypeConversion()->TryStaticEvaluation();
- if (constant != nullptr) {
- inst->ReplaceWith(constant);
- inst->GetBlock()->RemoveInstruction(inst);
- }
- } else if (inst->IsDivZeroCheck()) {
- // We can safely remove the check if the input is a non-null constant.
- HDivZeroCheck* check = inst->AsDivZeroCheck();
- HInstruction* check_input = check->InputAt(0);
- if (check_input->IsConstant() && !check_input->AsConstant()->IsZero()) {
- check->ReplaceWith(check_input);
- check->GetBlock()->RemoveInstruction(check);
- }
- }
- }
+ visitor.VisitReversePostOrder();
+}
+
+
+void HConstantFoldingVisitor::VisitBasicBlock(HBasicBlock* block) {
+ // Traverse this block's instructions (phis don't need to be
+ // processed) in (forward) order and replace the ones that can be
+ // statically evaluated by a compile-time counterpart.
+ for (HInstructionIterator it(block->GetInstructions()); !it.Done(); it.Advance()) {
+ it.Current()->Accept(this);
}
}
+void HConstantFoldingVisitor::VisitUnaryOperation(HUnaryOperation* inst) {
+ // Constant folding: replace `op(a)' with a constant at compile
+ // time if `a' is a constant.
+ HConstant* constant = inst->TryStaticEvaluation();
+ if (constant != nullptr) {
+ inst->ReplaceWith(constant);
+ inst->GetBlock()->RemoveInstruction(inst);
+ }
+}
+
+void HConstantFoldingVisitor::VisitBinaryOperation(HBinaryOperation* inst) {
+ // Constant folding: replace `op(a, b)' with a constant at
+ // compile time if `a' and `b' are both constants.
+ HConstant* constant = inst->TryStaticEvaluation();
+ if (constant != nullptr) {
+ inst->ReplaceWith(constant);
+ inst->GetBlock()->RemoveInstruction(inst);
+ } else {
+ InstructionWithAbsorbingInputSimplifier simplifier(GetGraph());
+ inst->Accept(&simplifier);
+ }
+}
+
+void HConstantFoldingVisitor::VisitTypeConversion(HTypeConversion* inst) {
+ // Constant folding: replace `TypeConversion(a)' with a constant at
+ // compile time if `a' is a constant.
+ HConstant* constant = inst->AsTypeConversion()->TryStaticEvaluation();
+ if (constant != nullptr) {
+ inst->ReplaceWith(constant);
+ inst->GetBlock()->RemoveInstruction(inst);
+ }
+}
+
+void HConstantFoldingVisitor::VisitDivZeroCheck(HDivZeroCheck* inst) {
+ // We can safely remove the check if the input is a non-null constant.
+ HInstruction* check_input = inst->InputAt(0);
+ if (check_input->IsConstant() && !check_input->AsConstant()->IsZero()) {
+ inst->ReplaceWith(check_input);
+ inst->GetBlock()->RemoveInstruction(inst);
+ }
+}
+
+
void InstructionWithAbsorbingInputSimplifier::VisitShift(HBinaryOperation* instruction) {
DCHECK(instruction->IsShl() || instruction->IsShr() || instruction->IsUShr());
HInstruction* left = instruction->GetLeft();
diff --git a/compiler/optimizing/constant_folding.h b/compiler/optimizing/constant_folding.h
index 2698b2d690..e0bc6f73dc 100644
--- a/compiler/optimizing/constant_folding.h
+++ b/compiler/optimizing/constant_folding.h
@@ -26,6 +26,13 @@ namespace art {
* Optimization pass performing a simple constant-expression
* evaluation on the SSA form.
*
+ * Note that graph simplifications producing a constant should be
+ * implemented in art::HConstantFolding, while graph simplifications
+ * not producing constants should be implemented in
+ * art::InstructionSimplifier. (This convention is a choice that was
+ * made during the development of these parts of the compiler and is
+ * not bound by any technical requirement.)
+ *
* This class is named art::HConstantFolding to avoid name
* clashes with the art::ConstantPropagation class defined in
* compiler/dex/post_opt_passes.h.
diff --git a/compiler/optimizing/instruction_simplifier.h b/compiler/optimizing/instruction_simplifier.h
index cc4b6f6adc..7905104ed4 100644
--- a/compiler/optimizing/instruction_simplifier.h
+++ b/compiler/optimizing/instruction_simplifier.h
@@ -25,6 +25,13 @@ namespace art {
/**
* Implements optimizations specific to each instruction.
+ *
+ * Note that graph simplifications producing a constant should be
+ * implemented in art::HConstantFolding, while graph simplifications
+ * not producing constants should be implemented in
+ * art::InstructionSimplifier. (This convention is a choice that was
+ * made during the development of these parts of the compiler and is
+ * not bound by any technical requirement.)
*/
class InstructionSimplifier : public HOptimization {
public:
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