[PATCH] D125576: [LLVM][Casting.h] Add ForwardToPointerCast trait

[Aman LaChapelle via Phabricator via llvm-commits]

bzcheeseman created this revision.
Herald added subscribers: Chia-hungDuan, rriddle.
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bzcheeseman requested review of this revision.
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Addresses use cases in Clang/MLIR that need pointer-to-pointer, reference-to-reference, and value-to-value casts from/to the same types. This should reduce boilerplate by allowing the user to simply specify the pointer cast and forward the reference cast directly to the pointer cast.

This cast trait DOES NOT implement `castFailed` and `doCastIfPossible` because in the general case doing so could result in a nullptr dereference. Users can use `NullableValueCastFailed` and `DefaultDoCastIfPossible` as desired for those cases where `nullptr` is acceptable.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D125576

Files:
  llvm/include/llvm/Support/Casting.h


Index: llvm/include/llvm/Support/Casting.h
===================================================================
--- llvm/include/llvm/Support/Casting.h
+++ llvm/include/llvm/Support/Casting.h
@@ -408,6 +408,29 @@
   }
 };
 
+/// Provides a cast trait that uses a defined pointer to pointer cast as a base
+/// for reference-to-reference casts. Note that it does not provide castFailed
+/// and doCastIfPossible because a pointer-to-pointer cast would likely just
+/// return `nullptr` which could cause nullptr dereference. You can use it like
+/// this:
+///
+///   template <> struct CastInfo<foo, bar *> { ... verbose implementation... };
+///
+///   template <>
+///   struct CastInfo<foo, bar>
+///       : public ForwardToPointerCast<foo, bar, CastInfo<foo, bar *>> {};
+///
+template <typename To, typename From, typename ForwardTo>
+struct ForwardToPointerCast {
+  static inline bool isPossible(const From &f) {
+    return ForwardTo::isPossible(&f);
+  }
+
+  static inline decltype(auto) doCast(const From &f) {
+    return *ForwardTo::doCast(&f);
+  }
+};
+
 //===----------------------------------------------------------------------===//
 // CastInfo
 //===----------------------------------------------------------------------===//


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