[all-commits] [llvm/llvm-project] a1ca69: [AArch64] recognise zip1/zip2 with flipped operand...

[Philip Ginsbach-Chen via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: a1ca69098d6c02c5d7f5a54f84a54636522b38be
      https://github.com/llvm/llvm-project/commit/a1ca69098d6c02c5d7f5a54f84a54636522b38be
  Author: Philip Ginsbach-Chen <philip.ginsbach at cantab.net>
  Date:   2025-11-27 (Thu, 27 Nov 2025)

  Changed paths:
    M llvm/lib/Target/AArch64/AArch64ISelLowering.cpp
    M llvm/lib/Target/AArch64/AArch64PerfectShuffle.h
    M llvm/lib/Target/AArch64/AArch64TargetTransformInfo.cpp
    M llvm/lib/Target/AArch64/GISel/AArch64PostLegalizerLowering.cpp
    M llvm/test/CodeGen/AArch64/arm64-zip.ll
    M llvm/test/CodeGen/AArch64/fixed-vector-deinterleave.ll
    M llvm/test/CodeGen/AArch64/insert-extend.ll
    M llvm/test/CodeGen/AArch64/insert-subvector.ll
    M llvm/test/CodeGen/AArch64/neon-widen-shuffle.ll
    M llvm/test/CodeGen/AArch64/reduce-shuffle.ll

  Log Message:
  -----------
  [AArch64] recognise zip1/zip2 with flipped operands (#167235)

Currently, the following two snippets get treated very differently from
each other (https://godbolt.org/z/rYGj9TGz6):
```LLVM
define <8 x i8> @foo(<8 x i8> %x, <8 x i8> %y) local_unnamed_addr #0 {
entry:
  %0 = shufflevector <8 x i8> %x, <8 x i8> %y, <8 x i32>
       <i32 0, i32 8, i32 1, i32 9, i32 2, i32 10, i32 3, i32 11>
  ret <8 x i8> %0
}

define <8 x i8> @bar(<8 x i8> %x, <8 x i8> %y) local_unnamed_addr #0 {
entry:
  %0 = shufflevector <8 x i8> %x, <8 x i8> %y, <8 x i32>
       <i32 8, i32 0, i32 9, i32 1, i32 10, i32 2, i32 11, i32 3>
  ret <8 x i8> %0
}
```
```
foo:                                    // @foo
        zip1    v0.8b, v0.8b, v1.8b
        ret
.LCPI1_0:
        .byte   8                               // 0x8
        .byte   0                               // 0x0
        .byte   9                               // 0x9
        .byte   1                               // 0x1
        .byte   10                              // 0xa
        .byte   2                               // 0x2
        .byte   11                              // 0xb
        .byte   3                               // 0x3
bar:                                    // @bar
        adrp    x8, .LCPI1_0
        mov     v0.d[1], v1.d[0]
        ldr     d1, [x8, :lo12:.LCPI1_0]
        tbl     v0.8b, { v0.16b }, v1.8b
        ret
```
The reason is that `isZIPMask` does not recognise the pattern when the
operands are flipped.

This PR fixes `isZIPMask` so that both `foo` and `bar` get compiled as
expected:
```
foo:                                    // @foo
	zip1	v0.8b, v0.8b, v1.8b
	ret
bar:                                    // @bar
	zip1	v0.8b, v1.8b, v0.8b
	ret
```

I intend to open a similar follow-up PR for `isTRNMask`, which seems to
have the same problem.

I noticed this while working on
https://github.com/llvm/llvm-project/issues/137447, though the change
does not on itself fix that issue.



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