[ADT] PointerUnion::getAddrOfPtr1(): fix/silence -Wcast-qual warning.

[lebedev.ri]

Summary

Previously, when D33102 landed, this broke -Werror buildbots.

http://lab.llvm.org:8011/builders/clang-with-lto-ubuntu/builds/3249

FAILED: /home/buildbot/Buildbot/Slave1a/clang-with-lto-ubuntu/install/stage1/bin/clang++   -DGTEST_HAS_RTTI=0 -DLLVM_BUILD_GLOBAL_ISEL -D_DEBUG -D_GNU_SOURCE -D__STDC_CONSTANT_MACROS -D__STDC_FORMAT_MACROS -D__STDC_LIMIT_MACROS -Ilib/CodeGen/AsmPrinter -I/home/buildbot/Buildbot/Slave1a/clang-with-lto-ubuntu/llvm.src/lib/CodeGen/AsmPrinter -Iinclude -I/home/buildbot/Buildbot/Slave1a/clang-with-lto-ubuntu/llvm.src/include -fPIC -fvisibility-inlines-hidden -Werror -Werror=date-time -std=c++11 -Wall -W -Wno-unused-parameter -Wwrite-strings -Wcast-qual -Wmissing-field-initializers -pedantic -Wno-long-long -Wcovered-switch-default -Wnon-virtual-dtor -Wdelete-non-virtual-dtor -Wstring-conversion -fcolor-diagnostics -ffunction-sections -fdata-sections -O3    -UNDEBUG  -fno-exceptions -fno-rtti -MMD -MT lib/CodeGen/AsmPrinter/CMakeFiles/LLVMAsmPrinter.dir/CodeViewDebug.cpp.o -MF lib/CodeGen/AsmPrinter/CMakeFiles/LLVMAsmPrinter.dir/CodeViewDebug.cpp.o.d -o lib/CodeGen/AsmPrinter/CMakeFiles/LLVMAsmPrinter.dir/CodeViewDebug.cpp.o -c /home/buildbot/Buildbot/Slave1a/clang-with-lto-ubuntu/llvm.src/lib/CodeGen/AsmPrinter/CodeViewDebug.cpp
In file included from /home/buildbot/Buildbot/Slave1a/clang-with-lto-ubuntu/llvm.src/lib/CodeGen/AsmPrinter/CodeViewDebug.cpp:14:
In file included from /home/buildbot/Buildbot/Slave1a/clang-with-lto-ubuntu/llvm.src/lib/CodeGen/AsmPrinter/CodeViewDebug.h:17:
In file included from /home/buildbot/Buildbot/Slave1a/clang-with-lto-ubuntu/llvm.src/lib/CodeGen/AsmPrinter/DbgValueHistoryCalculator.h:15:
In file included from /home/buildbot/Buildbot/Slave1a/clang-with-lto-ubuntu/llvm.src/include/llvm/IR/DebugInfoMetadata.h:26:
In file included from /home/buildbot/Buildbot/Slave1a/clang-with-lto-ubuntu/llvm.src/include/llvm/IR/Metadata.h:23:
/home/buildbot/Buildbot/Slave1a/clang-with-lto-ubuntu/llvm.src/include/llvm/ADT/PointerUnion.h:161:19: error: cast from 'void **' to 'const llvm::DISubprogram **' must have all intermediate pointers const qualified to be safe [-Werror,-Wcast-qual]
    return (PT1 *)Val.getAddrOfPointer();
                  ^
/home/buildbot/Buildbot/Slave1a/clang-with-lto-ubuntu/llvm.src/include/llvm/ADT/TinyPtrVector.h:177:18: note: in instantiation of member function 'llvm::PointerUnion<const llvm::DISubprogram *, llvm::SmallVector<const llvm::DISubprogram *, 4> *>::getAddrOfPtr1' requested here
      return Val.getAddrOfPtr1();
                 ^
/home/buildbot/Buildbot/Slave1a/clang-with-lto-ubuntu/llvm.src/lib/CodeGen/AsmPrinter/CodeViewDebug.cpp:1885:33: note: in instantiation of member function 'llvm::TinyPtrVector<const llvm::DISubprogram *>::begin' requested here
    for (const DISubprogram *SP : MethodItr.second) {
                                ^
1 error generated.

[dblaikie]

I'd probably go with const_cast + reinterpret_cast, rather than C-style cast. To be clear which conversions are happening.

[lebedev.ri]

Address review notes: replaced C-style cast with reinterpret_cast<>()

llvm/trunk/include/llvm/ADT/PointerUnion.h

public:
 
   /// If the union is set to the first pointer type get an address pointing to
   /// it.
   PT1 *getAddrOfPtr1() {
     assert(is<PT1>() && "Val is not the first pointer");
     assert(
         get<PT1>() == Val.getPointer() &&
         "Can't get the address because PointerLikeTypeTraits changes the ptr");
-    return (PT1 *)Val.getAddrOfPointer();
+    return const_cast<PT1 *>(reinterpret_cast<const PT1 *>(Val.getAddrOfPointer()));
   }
 
   /// Assignment from nullptr which just clears the union.
   const PointerUnion &operator=(std::nullptr_t) {
     Val.initWithPointer(nullptr);
     return *this;
   }