[PATCH] D149946: [LoongArch] Define `ual` feature and override `allowsMisalignedMemoryAccesses`

[Lu Weining via Phabricator via cfe-commits]

SixWeining created this revision.
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Some CPUs do not allow memory accesses to be unaligned, e.g. 2k1000la
who uses the la264 core on which misaligned access will trigger an
exception.

In this patch, a backend feature called `ual` is defined to decribe
whether the CPU supports unaligned memroy accesses. And this feature
can be toggled by clang options `-m[no-]unaligned-access` or the
aliases `-m[no-]strict-align`. When this feature is on,
`allowsMisalignedMemoryAccesses` sets the speed number to 1 and returns
true that allows the codegen to generate unaligned memory access insns.

Clang options `-m[no-]unaligned-access` are moved from `m_arm_Features_Group`
to `m_Group` because now more than one targets use them. In addition,
to keep compatible with gcc, a new alias `-mno-strict-align` is added
which is equal to `-munaligned-access`.

The feature name `ual` is consistent with linux kernel [1] and the
output of `lscpu` or `/proc/cpuinfo` [2].

There is an `LLT` variant of `allowsMisalignedMemoryAccesses`, but
seems that curently it is only used in GlobalISel which LoongArch
doesn't support yet. So this variant is not implemented in this patch.

[1]: https://github.com/torvalds/linux/blob/master/arch/loongarch/include/asm/cpu.h#L77
[2]: https://github.com/torvalds/linux/blob/master/arch/loongarch/kernel/proc.c#L75


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D149946

Files:
  clang/include/clang/Driver/Options.td
  clang/lib/Driver/ToolChains/Arch/LoongArch.cpp
  clang/test/Driver/loongarch-default-features.c
  clang/test/Driver/loongarch-march.c
  clang/test/Driver/loongarch-mdouble-float.c
  clang/test/Driver/loongarch-mfpu.c
  clang/test/Driver/loongarch-msingle-float.c
  clang/test/Driver/loongarch-msoft-float.c
  clang/test/Driver/loongarch-munaligned-access.c
  llvm/include/llvm/TargetParser/LoongArchTargetParser.def
  llvm/include/llvm/TargetParser/LoongArchTargetParser.h
  llvm/lib/Target/LoongArch/LoongArch.td
  llvm/lib/Target/LoongArch/LoongArchISelLowering.cpp
  llvm/lib/Target/LoongArch/LoongArchISelLowering.h
  llvm/lib/Target/LoongArch/LoongArchSubtarget.h
  llvm/test/CodeGen/LoongArch/calling-conv-lp64d.ll
  llvm/test/CodeGen/LoongArch/ir-instruction/atomicrmw-fp.ll
  llvm/test/CodeGen/LoongArch/tail-calls.ll
  llvm/test/CodeGen/LoongArch/unaligned-access.ll
  llvm/test/CodeGen/LoongArch/unaligned-memcpy-inline.ll

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