src/hotspot/share/opto/subnode.cpp

rev 51704 : 8210152: Optimize integer divisible by power-of-2 check
Summary: Integer conditional negation operation before zero check is eliminated
Reviewed-by: duke
Contributed-by: pengfei.li@arm.com

*** 1520,1529 ****
--- 1520,1560 ----
      const TypeInt* cmp1_in2 = phase->type(cmp1->in(2))->is_int();
      Node *ncmp = phase->transform( new CmpINode(cmp1->in(1),phase->intcon(-cmp1_in2->_hi)));
      return new BoolNode( ncmp, _test._test );
    }
  
+   // Change "bool eq/ne (cmp (phi (X -X) 0))" into "bool eq/ne (cmp X 0)"
+   // since zero check of conditional negation of an integer is equal to
+   // zero check of the integer directly.
+   if( (_test._test == BoolTest::eq || _test._test == BoolTest::ne) &&
+       (cop == Op_CmpI) &&
+       (cmp2_type == TypeInt::ZERO) &&
+       (cmp1_op == Op_Phi) ) {
+     // There should be a diamond phi with true path at index 1 or 2
+     PhiNode *phi = cmp1->as_Phi();
+     int idx_true = phi->is_diamond_phi();
+     if ( idx_true != 0 ) {
+       // True input is in(idx_true) while false input is in(3 - idx_true)
+       Node *tin = phi->in(idx_true);
+       Node *fin = phi->in(3 - idx_true);
+       if( (tin->Opcode() == Op_SubI) &&
+           (phase->type(tin->in(1)) == TypeInt::ZERO) &&
+           (tin->in(2) == fin) ) {
+         // Found conditional negation at true path, create a new CmpINode without that
+         Node *ncmp = phase->transform( new CmpINode(fin, cmp2) );
+         return new BoolNode( ncmp, _test._test );
+       }
+       if( (fin->Opcode() == Op_SubI) &&
+           (phase->type(fin->in(1)) == TypeInt::ZERO) &&
+           (fin->in(2) == tin) ) {
+         // Found conditional negation at false path, create a new CmpINode without that
+         Node *ncmp = phase->transform( new CmpINode(tin, cmp2) );
+         return new BoolNode( ncmp, _test._test );
+       }
+     }
+   }
+ 
    // Change (-A vs 0) into (A vs 0) by commuting the test.  Disallow in the
    // most general case because negating 0x80000000 does nothing.  Needed for
    // the CmpF3/SubI/CmpI idiom.
    if( cop == Op_CmpI &&
        cmp1_op == Op_SubI &&