[PATCH] D124571: Avoid strict aliasing violation on type punning inside llvm::PointerIntPair

[Breno Rodrigues Guimaraes via Phabricator via llvm-commits]

brenoguim updated this revision to Diff 425939.
brenoguim added a comment.

- Updated variable names on test to start with upper case
- Added static_assert to check sizeof(Ptr) == sizeof(intptr)
- Added constexpr to toInt method so all are constexpr now, just in case
- Changed the underlying storage to be Ptr, removing the interpret cast


CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D124571/new/

https://reviews.llvm.org/D124571

Files:
  llvm/include/llvm/ADT/PointerIntPair.h
  llvm/unittests/ADT/PointerIntPairTest.cpp


Index: llvm/unittests/ADT/PointerIntPairTest.cpp
===================================================================
--- llvm/unittests/ADT/PointerIntPairTest.cpp
+++ llvm/unittests/ADT/PointerIntPairTest.cpp
@@ -106,4 +106,22 @@
       "trivially copyable");
 }
 
+TEST(PointerIntPairTest, TypePunning) {
+  int I = 0;
+  int *IntPtr = &I;
+
+  int **IntPtrBegin = &IntPtr;
+  int **IntPtrEnd = IntPtrBegin + 1;
+
+  PointerIntPair<int *, 1> Pair;
+  int **PairAddr = Pair.getAddrOfPointer();
+
+  while (IntPtrBegin != IntPtrEnd) {
+    *PairAddr = *IntPtrBegin;
+    ++PairAddr;
+    ++IntPtrBegin;
+  }
+  EXPECT_EQ(Pair.getPointer(), IntPtr);
+}
+
 } // end anonymous namespace
Index: llvm/include/llvm/ADT/PointerIntPair.h
===================================================================
--- llvm/include/llvm/ADT/PointerIntPair.h
+++ llvm/include/llvm/ADT/PointerIntPair.h
@@ -19,10 +19,38 @@
 #include "llvm/Support/type_traits.h"
 #include <cassert>
 #include <cstdint>
+#include <cstring>
 #include <limits>
 
 namespace llvm {
 
+namespace detail {
+template <typename Ptr> struct PunnedPointer {
+  static_assert(sizeof(Ptr) == sizeof(intptr_t), "");
+
+  explicit constexpr PunnedPointer(intptr_t i = 0) { *this = i; }
+
+  constexpr intptr_t asInt() const {
+    intptr_t R = 0;
+    std::memcpy(&R, &Data, sizeof(R));
+    return R;
+  }
+
+  constexpr operator intptr_t() const { return asInt(); }
+
+  constexpr PunnedPointer &operator=(intptr_t V) {
+    std::memcpy(&Data, &V, sizeof(Data));
+    return *this;
+  }
+
+  Ptr *getPointerAddress() { return &Data; }
+  const Ptr *getPointerAddress() const { return &Data; }
+
+private:
+  Ptr Data;
+};
+} // namespace detail
+
 template <typename T, typename Enable> struct DenseMapInfo;
 template <typename PointerT, unsigned IntBits, typename PtrTraits>
 struct PointerIntPairInfo;
@@ -46,7 +74,7 @@
 class PointerIntPair {
   // Used by MSVC visualizer and generally helpful for debugging/visualizing.
   using InfoTy = Info;
-  intptr_t Value = 0;
+  detail::PunnedPointer<PointerTy> Value;
 
 public:
   constexpr PointerIntPair() = default;
@@ -86,10 +114,12 @@
     assert(Value == reinterpret_cast<intptr_t>(getPointer()) &&
            "Can only return the address if IntBits is cleared and "
            "PtrTraits doesn't change the pointer");
-    return reinterpret_cast<PointerTy *>(&Value);
+    return Value.getPointerAddress();
   }
 
-  void *getOpaqueValue() const { return reinterpret_cast<void *>(Value); }
+  void *getOpaqueValue() const {
+    return reinterpret_cast<void *>(Value.asInt());
+  }
 
   void setFromOpaqueValue(void *Val) & {
     Value = reinterpret_cast<intptr_t>(Val);


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