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

@@ -1520,10 +1520,41 @@
     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 &&