8160404: RelocationHolder constructors have bugs

Reviewed-by: kvn, jrose, jvernee

src/hotspot/cpu/x86/assembler_x86.cpp

@@ -2495,7 +2495,7 @@ void Assembler::jmp_literal(address dest, RelocationHolder const& rspec) {
   assert(dest != NULL, "must have a target");
   intptr_t disp = dest - (pc() + sizeof(int32_t));
   assert(is_simm32(disp), "must be 32bit offset (jmp)");
-  emit_data(disp, rspec.reloc(), call32_operand);
+  emit_data(disp, rspec, call32_operand);
 }
 
 void Assembler::jmpb_0(Label& L, const char* file, int line) {

src/hotspot/share/code/relocInfo.cpp

@@ -36,6 +36,9 @@
 #include "utilities/align.hpp"
 #include "utilities/copy.hpp"
 
+#include <new>
+#include <type_traits>
+
 const RelocationHolder RelocationHolder::none; // its type is relocInfo::none
 
 
@@ -235,12 +238,44 @@ Relocation* RelocIterator::reloc() {
   APPLY_TO_RELOCATIONS(EACH_TYPE);
   #undef EACH_TYPE
   assert(t == relocInfo::none, "must be padding");
-  return new(_rh) Relocation(t);
+  _rh = RelocationHolder::none;
+  return _rh.reloc();
 }
 
+// Verify all the destructors are trivial, so we don't need to worry about
+// destroying old contents of a RelocationHolder being assigned or destroyed.
+#define VERIFY_TRIVIALLY_DESTRUCTIBLE_AUX(Reloc) \
+  static_assert(std::is_trivially_destructible<Reloc>::value, "must be");
 
-//////// Methods for flyweight Relocation types
+#define VERIFY_TRIVIALLY_DESTRUCTIBLE(name) \
+  VERIFY_TRIVIALLY_DESTRUCTIBLE_AUX(PASTE_TOKENS(name, _Relocation));
+
+APPLY_TO_RELOCATIONS(VERIFY_TRIVIALLY_DESTRUCTIBLE)
+VERIFY_TRIVIALLY_DESTRUCTIBLE_AUX(Relocation)
+
+#undef VERIFY_TRIVIALLY_DESTRUCTIBLE_AUX
+#undef VERIFY_TRIVIALLY_DESTRUCTIBLE
+
+// Define all the copy_into functions.  These rely on all Relocation types
+// being trivially destructible (verified above).  So it doesn't matter
+// whether the target holder has been previously initialized or not.  There's
+// no need to consider that distinction and destruct the relocation in an
+// already initialized holder.
+#define DEFINE_COPY_INTO_AUX(Reloc)                             \
+  void Reloc::copy_into(RelocationHolder& holder) const {       \
+    copy_into_helper(*this, holder);                            \
+  }
 
+#define DEFINE_COPY_INTO(name) \
+  DEFINE_COPY_INTO_AUX(PASTE_TOKENS(name, _Relocation))
+
+APPLY_TO_RELOCATIONS(DEFINE_COPY_INTO)
+DEFINE_COPY_INTO_AUX(Relocation)
+
+#undef DEFINE_COPY_INTO_AUX
+#undef DEFINE_COPY_INTO
+
+//////// Methods for RelocationHolder
 
 RelocationHolder RelocationHolder::plus(int offset) const {
   if (offset != 0) {
@@ -264,6 +299,8 @@ RelocationHolder RelocationHolder::plus(int offset) const {
   return (*this);
 }
 
+//////// Methods for flyweight Relocation types
+
 // some relocations can compute their own values
 address Relocation::value() {
   ShouldNotReachHere();