[all-commits] [llvm/llvm-project] bb03cd: RISCV: Remove shouldForceRelocation and unneeded r...

[Fangrui Song via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: bb03cdcb441fd68da9d1ebb7d5f39f73667cd39c
      https://github.com/llvm/llvm-project/commit/bb03cdcb441fd68da9d1ebb7d5f39f73667cd39c
  Author: Fangrui Song <i at maskray.me>
  Date:   2025-05-23 (Fri, 23 May 2025)

  Changed paths:
    M bolt/test/RISCV/reloc-label-diff.s
    M bolt/test/RISCV/reorder-blocks-reverse.s
    M llvm/include/llvm/MC/MCAssembler.h
    M llvm/include/llvm/MC/MCFixup.h
    M llvm/include/llvm/MC/MCSection.h
    M llvm/lib/MC/MCAssembler.cpp
    M llvm/lib/MC/MCELFStreamer.cpp
    M llvm/lib/MC/MCExpr.cpp
    M llvm/lib/MC/MCSection.cpp
    M llvm/lib/Target/LoongArch/MCTargetDesc/LoongArchAsmBackend.cpp
    M llvm/lib/Target/LoongArch/MCTargetDesc/LoongArchMCCodeEmitter.cpp
    M llvm/lib/Target/RISCV/AsmParser/RISCVAsmParser.cpp
    M llvm/lib/Target/RISCV/MCTargetDesc/RISCVAsmBackend.cpp
    M llvm/lib/Target/RISCV/MCTargetDesc/RISCVAsmBackend.h
    M llvm/lib/Target/RISCV/MCTargetDesc/RISCVELFStreamer.cpp
    M llvm/lib/Target/RISCV/MCTargetDesc/RISCVMCCodeEmitter.cpp
    M llvm/test/CodeGen/RISCV/option-relax-relocation.ll
    M llvm/test/MC/RISCV/fixups-binary-expression.s
    M llvm/test/MC/RISCV/linker-relaxation.s
    M llvm/test/MC/RISCV/long-conditional-jump.s
    M llvm/test/MC/RISCV/option-relax.s
    M llvm/test/MC/RISCV/xqcibi-long-conditional-jump.s

  Log Message:
  -----------
  RISCV: Remove shouldForceRelocation and unneeded relocations

Follow-up to #140494

`shouldForceRelocation` is conservative and produces redundant
relocations.

For example, RISCVAsmBackend::ForceRelocs (introduced to support mixed
relax/norelax code) leads to redundant relocations in the following
example adapted from #77436

```
.option norelax
j label
// For assembly input, RISCVAsmParser::ParseInstruction sets ForceRelocs (https://reviews.llvm.org/D46423).
// For direct object emission, RISCVELFStreamer sets ForceRelocs (#77436)
.option relax
call foo  // linker-relaxable

.option norelax
j label   // redundant relocation due to ForceRelocs
.option relax

label:
```

Root problem: The `isSymbolRefDifferenceFullyResolvedImpl` condition in
MCAssembler::evaluateFixup does not check whether two locations are
separated by a fragment whose size can be indeterminate due to linker
instruction (e.g. MCDataFragment with relaxation, or MCAlignFragment
due to indeterminate start offst).

This patch

* Updates the fragment walk code in
  `attemptToFoldSymbolOffsetDifference` to treat MCRelaxableFragment
  (for --riscv-asm-relax-branches) as fixed size after finishLayout.
* Adds a condition in `addReloc` to complement
  `isSymbolRefDifferenceFullyResolvedImpl`.
* Removes the no longer needed `shouldForceRelocation`.

This fragment walk code path handles nicely handles
mixed relax/norelax case from
https://discourse.llvm.org/t/possible-problem-related-to-subtarget-usage/75283
and allows us to remove `MCSubtargetInfo` argument (#73721) as a follow-up.

This fragment walk code should be avoided in the absence of
linker-relaxable fragments within the current section.

Adjust two bolt/test/RISCV tests (#141310)

Pull Request: https://github.com/llvm/llvm-project/pull/140692



To unsubscribe from these emails, change your notification settings at https://github.com/llvm/llvm-project/settings/notifications