[all-commits] [llvm/llvm-project] a62b86: [AArch64, ELF] Restrict MOVZ/MOVK to non-PIC large ...

[Fangrui Song via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: a62b86a3e66f6e328adc88bbd3a0c8b1991d35bb
      https://github.com/llvm/llvm-project/commit/a62b86a3e66f6e328adc88bbd3a0c8b1991d35bb
  Author: Fangrui Song <i at maskray.me>
  Date:   2023-11-01 (Wed, 01 Nov 2023)

  Changed paths:
    M llvm/lib/Target/AArch64/AArch64ISelLowering.cpp
    M llvm/lib/Target/AArch64/GISel/AArch64InstructionSelector.cpp
    M llvm/test/CodeGen/AArch64/GlobalISel/select-blockaddress.mir
    M llvm/test/CodeGen/AArch64/GlobalISel/select-gv-cmodel-large.mir
    M llvm/test/CodeGen/AArch64/GlobalISel/select-gv-with-offset.mir
    M llvm/test/CodeGen/AArch64/blockaddress.ll
    R llvm/test/CodeGen/AArch64/code-model-large-abs.ll
    A llvm/test/CodeGen/AArch64/code-model-large.ll
    M llvm/test/CodeGen/AArch64/jump-table.ll

  Log Message:
  -----------
  [AArch64,ELF] Restrict MOVZ/MOVK to non-PIC large code model (#70178)

There is no PIC support for -mcmodel=large

(https://github.com/ARM-software/abi-aa/blob/main/sysvabi64/sysvabi64.rst)
and Clang recently rejects -mcmodel= with PIC (#70262).

The current backend code assumes that the large code model is non-PIC.
This patch adds `!getTargetMachine().isPositionIndependent()` conditions
to clarify that the support is non-PIC only. In addition, add some tests
as change detectors in case PIC large code model is supported in the
future.

If other front-ends/JITs use the large code model with PIC, they will
get small code model code sequence, instead of potentially-incorrect
MOVZ/MOVK sequence, which is only suitable for non-PIC. The sequence
will cause text relocations using ELF linkers.

(The small code model code sequence is usually sufficient as ADRP+ADD or
ADRP+LDR targets [-2**32,2**32), which has a doubled range of x86-64
R_X86_64_REX_GOTPCRELX/R_X86_64_PC32 [-2**32,2**32).)