src/share/vm/opto/compile.cpp

rev 10974 : 8155729: C2: Skip transformation of LoadConP for heap-based compressed oops
Reviewed-by:

*** 2850,2868 ****
  #ifdef _LP64
      if ((UseCompressedOops || UseCompressedClassPointers) &&
          addp->Opcode() == Op_ConP &&
          addp == n->in(AddPNode::Base) &&
          n->in(AddPNode::Offset)->is_Con()) {
        // Use addressing with narrow klass to load with offset on x86.
!       // On sparc loading 32-bits constant and decoding it have less
!       // instructions (4) then load 64-bits constant (7).
        // Do this transformation here since IGVN will convert ConN back to ConP.
        const Type* t = addp->bottom_type();
!       if (t->isa_oopptr() || t->isa_klassptr()) {
          Node* nn = NULL;
  
!         int op = t->isa_oopptr() ? Op_ConN : Op_ConNKlass;
  
          // Look for existing ConN node of the same exact type.
          Node* r  = root();
          uint cnt = r->outcnt();
          for (uint i = 0; i < cnt; i++) {
--- 2850,2873 ----
  #ifdef _LP64
      if ((UseCompressedOops || UseCompressedClassPointers) &&
          addp->Opcode() == Op_ConP &&
          addp == n->in(AddPNode::Base) &&
          n->in(AddPNode::Offset)->is_Con()) {
+       // If the transformation of ConP to ConN+DecodeN is beneficial depends
+       // on the platform and on the compressed oops mode.
        // Use addressing with narrow klass to load with offset on x86.
!       // Some platforms can use the constant pool to load ConP.
        // Do this transformation here since IGVN will convert ConN back to ConP.
        const Type* t = addp->bottom_type();
!       bool is_oop   = t->isa_oopptr(),
!            is_klass = t->isa_klassptr();
! 
!       if ((is_oop   && Matcher::const_oop_prefer_decode()  ) ||
!           (is_klass && Matcher::const_klass_prefer_decode())) {
          Node* nn = NULL;
  
!         int op = is_oop ? Op_ConN : Op_ConNKlass;
  
          // Look for existing ConN node of the same exact type.
          Node* r  = root();
          uint cnt = r->outcnt();
          for (uint i = 0; i < cnt; i++) {
*** 2874,2884 ****
            }
          }
          if (nn != NULL) {
            // Decode a narrow oop to match address
            // [R12 + narrow_oop_reg<<3 + offset]
!           if (t->isa_oopptr()) {
              nn = new DecodeNNode(nn, t);
            } else {
              nn = new DecodeNKlassNode(nn, t);
            }
            // Check for succeeding AddP which uses the same Base.
--- 2879,2889 ----
            }
          }
          if (nn != NULL) {
            // Decode a narrow oop to match address
            // [R12 + narrow_oop_reg<<3 + offset]
!           if (is_oop) {
              nn = new DecodeNNode(nn, t);
            } else {
              nn = new DecodeNKlassNode(nn, t);
            }
            // Check for succeeding AddP which uses the same Base.