6991577: add IfOp optimization to C1

Summary: Ifop optimization for c1
Reviewed-by: never, phh, iveresov

src/share/vm/c1/c1_Compilation.hpp

@@ -178,15 +178,11 @@ class Compilation: public StackObj {
     return (int) NMethodSizeLimit;  // default 256K or 512K
 #else
     // conditional branches on PPC are restricted to 16 bit signed
-    return MAX2((unsigned int)NMethodSizeLimit,32*K);
+    return MIN2((unsigned int)NMethodSizeLimit,32*K);
 #endif
   }
   static int desired_max_constant_size() {
-#ifndef PPC
-    return (int) NMethodSizeLimit / 10;  // about 25K
-#else
-    return (MAX2((unsigned int)NMethodSizeLimit, 32*K)) / 10;
-#endif
+    return desired_max_code_buffer_size() / 10;
   }
 
   static void setup_code_buffer(CodeBuffer* cb, int call_stub_estimate);

src/share/vm/c1/c1_IR.cpp

@@ -321,7 +321,7 @@ class UseCountComputer: public ValueVisitor, BlockClosure {
   void visit(Value* n) {
     // Local instructions and Phis for expression stack values at the
     // start of basic blocks are not added to the instruction list
-    if (!(*n)->is_linked()&& (*n)->can_be_linked()) {
+    if (!(*n)->is_linked() && (*n)->can_be_linked()) {
       assert(false, "a node was not appended to the graph");
       Compilation::current()->bailout("a node was not appended to the graph");
     }

src/share/vm/c1/c1_Instruction.cpp

@@ -415,28 +415,26 @@ bool Constant::is_equal(Value v) const {
   return false;
 }
 
-
-BlockBegin* Constant::compare(Instruction::Condition cond, Value right,
-                              BlockBegin* true_sux, BlockBegin* false_sux) {
+Constant::CompareResult Constant::compare(Instruction::Condition cond, Value right) const {
   Constant* rc = right->as_Constant();
   // other is not a constant
-  if (rc == NULL) return NULL;
+  if (rc == NULL) return not_comparable;
 
   ValueType* lt = type();
   ValueType* rt = rc->type();
   // different types
-  if (lt->base() != rt->base()) return NULL;
+  if (lt->base() != rt->base()) return not_comparable;
   switch (lt->tag()) {
   case intTag: {
     int x = lt->as_IntConstant()->value();
     int y = rt->as_IntConstant()->value();
     switch (cond) {
-    case If::eql: return x == y ? true_sux : false_sux;
-    case If::neq: return x != y ? true_sux : false_sux;
-    case If::lss: return x <  y ? true_sux : false_sux;
-    case If::leq: return x <= y ? true_sux : false_sux;
-    case If::gtr: return x >  y ? true_sux : false_sux;
-    case If::geq: return x >= y ? true_sux : false_sux;
+    case If::eql: return x == y ? cond_true : cond_false;
+    case If::neq: return x != y ? cond_true : cond_false;
+    case If::lss: return x <  y ? cond_true : cond_false;
+    case If::leq: return x <= y ? cond_true : cond_false;
+    case If::gtr: return x >  y ? cond_true : cond_false;
+    case If::geq: return x >= y ? cond_true : cond_false;
     }
     break;
   }
@@ -444,12 +442,12 @@ BlockBegin* Constant::compare(Instruction::Condition cond, Value right,
     jlong x = lt->as_LongConstant()->value();
     jlong y = rt->as_LongConstant()->value();
     switch (cond) {
-    case If::eql: return x == y ? true_sux : false_sux;
-    case If::neq: return x != y ? true_sux : false_sux;
-    case If::lss: return x <  y ? true_sux : false_sux;
-    case If::leq: return x <= y ? true_sux : false_sux;
-    case If::gtr: return x >  y ? true_sux : false_sux;
-    case If::geq: return x >= y ? true_sux : false_sux;
+    case If::eql: return x == y ? cond_true : cond_false;
+    case If::neq: return x != y ? cond_true : cond_false;
+    case If::lss: return x <  y ? cond_true : cond_false;
+    case If::leq: return x <= y ? cond_true : cond_false;
+    case If::gtr: return x >  y ? cond_true : cond_false;
+    case If::geq: return x >= y ? cond_true : cond_false;
     }
     break;
   }
@@ -459,14 +457,14 @@ BlockBegin* Constant::compare(Instruction::Condition cond, Value right,
     assert(xvalue != NULL && yvalue != NULL, "not constants");
     if (xvalue->is_loaded() && yvalue->is_loaded()) {
       switch (cond) {
-      case If::eql: return xvalue == yvalue ? true_sux : false_sux;
-      case If::neq: return xvalue != yvalue ? true_sux : false_sux;
+      case If::eql: return xvalue == yvalue ? cond_true : cond_false;
+      case If::neq: return xvalue != yvalue ? cond_true : cond_false;
       }
     }
     break;
   }
   }
-  return NULL;
+  return not_comparable;
 }
 
 

src/share/vm/c1/c1_Instruction.hpp

@@ -650,8 +650,24 @@ LEAF(Constant, Instruction)
   virtual intx hash() const;
   virtual bool is_equal(Value v) const;
 
-  virtual BlockBegin* compare(Instruction::Condition condition, Value right,
-                              BlockBegin* true_sux, BlockBegin* false_sux);
+
+  enum CompareResult { not_comparable = -1, cond_false, cond_true };
+
+  virtual CompareResult compare(Instruction::Condition condition, Value right) const;
+  BlockBegin* compare(Instruction::Condition cond, Value right,
+                      BlockBegin* true_sux, BlockBegin* false_sux) const {
+    switch (compare(cond, right)) {
+    case not_comparable:
+      return NULL;
+    case cond_false:
+      return false_sux;
+    case cond_true:
+      return true_sux;
+    default:
+      ShouldNotReachHere();
+      return NULL;
+    }
+  }
 };
 
 

src/share/vm/c1/c1_Optimizer.cpp

@@ -38,18 +38,20 @@ class CE_Eliminator: public BlockClosure {
  private:
   IR* _hir;
   int _cee_count;                                // the number of CEs successfully eliminated
+  int _ifop_count;                               // the number of IfOps successfully simplified
   int _has_substitution;
 
  public:
-  CE_Eliminator(IR* hir) : _cee_count(0), _hir(hir) {
+  CE_Eliminator(IR* hir) : _cee_count(0), _ifop_count(0), _hir(hir) {
     _has_substitution = false;
     _hir->iterate_preorder(this);
     if (_has_substitution) {
-      // substituted some phis so resolve the substitution
+      // substituted some ifops/phis, so resolve the substitution
       SubstitutionResolver sr(_hir);
     }
   }
   int cee_count() const                          { return _cee_count; }
+  int ifop_count() const                         { return _ifop_count; }
 
   void adjust_exception_edges(BlockBegin* block, BlockBegin* sux) {
     int e = sux->number_of_exception_handlers();
@@ -68,7 +70,13 @@ class CE_Eliminator: public BlockClosure {
     }
   }
 
-  virtual void block_do(BlockBegin* block) {
+  virtual void block_do(BlockBegin* block);
+
+ private:
+  Value make_ifop(Value x, Instruction::Condition cond, Value y, Value tval, Value fval);
+};
+
+void CE_Eliminator::block_do(BlockBegin* block) {
   // 1) find conditional expression
   // check if block ends with an If
   If* if_ = block->end()->as_If();
@@ -155,12 +163,12 @@ class CE_Eliminator: public BlockClosure {
     cur_end = cur_end->set_next(f_value);
   }
 
-    // it is very unlikely that the condition can be statically decided
-    // (this was checked previously by the Canonicalizer), so always
-    // append IfOp
-    Value result = new IfOp(if_->x(), if_->cond(), if_->y(), t_value, f_value);
+  Value result = make_ifop(if_->x(), if_->cond(), if_->y(), t_value, f_value);
+  assert(result != NULL, "make_ifop must return a non-null instruction");
+  if (!result->is_linked() && result->can_be_linked()) {
     NOT_PRODUCT(result->set_printable_bci(if_->printable_bci()));
     cur_end = cur_end->set_next(result);
+  }
 
   // append Goto to successor
   ValueStack* state_before = if_->is_safepoint() ? if_->state_before() : NULL;
@@ -205,19 +213,71 @@ class CE_Eliminator: public BlockClosure {
   _cee_count++;
   if (PrintCEE) {
     tty->print_cr("%d. CEE in B%d (B%d B%d)", cee_count(), block->block_id(), t_block->block_id(), f_block->block_id());
+    tty->print_cr("%d. IfOp in B%d", ifop_count(), block->block_id());
   }
 
   _hir->verify();
+}
+
+Value CE_Eliminator::make_ifop(Value x, Instruction::Condition cond, Value y, Value tval, Value fval) {
+  if (!OptimizeIfOps) {
+    return new IfOp(x, cond, y, tval, fval);
   }
-};
 
+  tval = tval->subst();
+  fval = fval->subst();
+  if (tval == fval) {
+    _ifop_count++;
+    return tval;
+  }
+
+  x = x->subst();
+  y = y->subst();
+
+  Constant* y_const = y->as_Constant();
+  if (y_const != NULL) {
+    IfOp* x_ifop = x->as_IfOp();
+    if (x_ifop != NULL) {                 // x is an ifop, y is a constant
+      Constant* x_tval_const = x_ifop->tval()->subst()->as_Constant();
+      Constant* x_fval_const = x_ifop->fval()->subst()->as_Constant();
+
+      if (x_tval_const != NULL && x_fval_const != NULL) {
+        Instruction::Condition x_ifop_cond = x_ifop->cond();
+
+        Constant::CompareResult t_compare_res = x_tval_const->compare(cond, y_const);
+        Constant::CompareResult f_compare_res = x_fval_const->compare(cond, y_const);
+
+        guarantee(t_compare_res != Constant::not_comparable && f_compare_res != Constant::not_comparable, "incomparable constants in IfOp");
+
+        Value new_tval = t_compare_res == Constant::cond_true ? tval : fval;
+        Value new_fval = f_compare_res == Constant::cond_true ? tval : fval;
+
+        _ifop_count++;
+        if (new_tval == new_fval) {
+          return new_tval;
+        } else {
+          return new IfOp(x_ifop->x(), x_ifop_cond, x_ifop->y(), new_tval, new_fval);
+        }
+      }
+    } else {
+      Constant* x_const = x->as_Constant();
+      if (x_const != NULL) {         // x and y are constants
+        Constant::CompareResult x_compare_res = x_const->compare(cond, y_const);
+        guarantee(x_compare_res != Constant::not_comparable, "incomparable constants in IfOp");
+
+        _ifop_count++;
+        return x_compare_res == Constant::cond_true ? tval : fval;
+      }
+    }
+  }
+  return new IfOp(x, cond, y, tval, fval);
+}
 
 void Optimizer::eliminate_conditional_expressions() {
   // find conditional expressions & replace them with IfOps
   CE_Eliminator ce(ir());
 }
 
-
 class BlockMerger: public BlockClosure {
  private:
   IR* _hir;

src/share/vm/c1/c1_globals.hpp

@@ -75,6 +75,9 @@
   develop(bool, SelectivePhiFunctions, true,                                \
           "create phi functions at loop headers only when necessary")       \
                                                                             \
+  develop(bool, OptimizeIfOps, true,                                        \
+          "Optimize multiple IfOps")                                        \
+                                                                            \
   develop(bool, DoCEE, true,                                                \
           "Do Conditional Expression Elimination to simplify CFG")          \
                                                                             \