llvm-project

46620f84 - Reland "[llvm][ADT] Refactor PointerUnion to use PunnedPointer. NFC." (#188242)

Reland "[llvm][ADT] Refactor PointerUnion to use PunnedPointer. NFC." (#188242) This reverts commit 040b7e0a1deb and re-lands the PointerUnion refactoring from #187950, with a fix for the 32-bit crash. The bug was in doCast: it masked with PointerLikeTypeTraits<To>::NumLowBitsAvailable to strip tag bits, but the old PointerIntPair-based code masked with minLowBitsAvailable() (the minimum across all union members). When a member type's PLTT over-claims spare low bits, the new mask was too aggressive and cleared bits belonging to a nested PointerUnion's tag. Concretely, on 32-bit systems, Redeclarable::DeclLink nests LazyGenerationalUpdatePtr (LGUP) whose PLTT claims 2 spare bits (Decl* has alignas(8) = 3 bits, minus 1). But LGUP's inner PointerUnion<Decl*, LazyData*> only has 1 spare bit on 32-bit (alignof(LazyData) = 4 gives LazyData* only 2 low bits, tagShift = 1). Extracting LGUP from the outer PointerUnion cleared bit 1 (the inner PU's type tag), corrupting the discriminator and breaking redeclaration chains. Added new unit tests that cover this scenario, but we will want to fix the clang side too. Issue: #188269 --------- Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>