[PATCH] D87916: [PowerPC][LLD] Extend R2 save stub to support offsets of more than 26 bits

[Stefan Pintilie via Phabricator via llvm-commits]

stefanp created this revision.
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The R2 <https://reviews.llvm.org/source/clang-tools-extra/> save stub will now support offsets up to 64 bits.

There are three cases that will be used.

1. The offset fits in 26 bits.

  b <26 bit offset>

2. The offset does not fit in 26 bits but fits in 34 bits.

  paddi r12, 0, <34 bit offset>, 1
  mtctr r12
  bctr

3. The offset does not fit in 34 bits. Since this is an R2 <https://reviews.llvm.org/source/clang-tools-extra/> save stub we can use

the TOC in R2 <https://reviews.llvm.org/source/clang-tools-extra/>. We are not loading the offset but the actual address we want to
branch to.

  addis r12, r2, <address in TOC lo>
  ld r12 <address in TOC hi>(r12)
  mtctr r12
  bctr

In case 1) the stub is only 8 bytes while in cases 2) and 3) the stub will be
20 bytes.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D87916

Files:
  lld/ELF/Thunks.cpp
  lld/test/ELF/ppc64-toc-call-to-pcrel-long-jump.s

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