[PATCH] D144943: [clang][Interp] Implement bitcasts (WIP)

[Timm Bäder via Phabricator via cfe-commits]

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This implements bitcasts by traversing the pointer fields at interpretation-time, copying them into a buffer and then either creating a new primitive value from the buffer, or traversing the destination pointer and reading the field values from that buffer.

This is a bit non-idiomatic to the new interpreter since we do so much work at interpretation time instead of doing it at compile-time.
I can imagine ways to change this, but it would require bytecode instructions that are rather awkward, I think. So this is my attempt at
doing it this way instead.

It's also missing all the eligibility checks for bitcasts of course.
I have also not tested this on a big-endian host, which I definitely need to do (is the bit rotation needed if the host is BE //and// the target is BE?).

I'll try to leave a few comments in the diff.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D144943

Files:
  clang/lib/AST/Interp/Boolean.h
  clang/lib/AST/Interp/ByteCodeExprGen.cpp
  clang/lib/AST/Interp/ByteCodeExprGen.h
  clang/lib/AST/Interp/Descriptor.h
  clang/lib/AST/Interp/Floating.h
  clang/lib/AST/Interp/Integral.h
  clang/lib/AST/Interp/Interp.h
  clang/lib/AST/Interp/InterpBuiltin.cpp
  clang/lib/AST/Interp/Opcodes.td
  clang/lib/AST/Interp/Pointer.cpp
  clang/lib/AST/Interp/Pointer.h
  clang/lib/AST/Interp/PrimType.h
  clang/test/AST/Interp/builtin-bit-cast.cpp

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