[all-commits] [llvm/llvm-project] c727b4: [SDAG][ISel][TableGen][LoongArch] Report error for...

[Yingwei Zheng via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: c727b48287cc96888f9e262f23d53cf635cf3b3d
      https://github.com/llvm/llvm-project/commit/c727b48287cc96888f9e262f23d53cf635cf3b3d
  Author: Yingwei Zheng <dtcxzyw2333 at gmail.com>
  Date:   2024-11-19 (Tue, 19 Nov 2024)

  Changed paths:
    M llvm/lib/Target/LoongArch/LoongArchLSXInstrInfo.td
    A llvm/test/CodeGen/LoongArch/lsx/pr116008.ll
    M llvm/utils/TableGen/Common/CodeGenDAGPatterns.cpp

  Log Message:
  -----------
  [SDAG][ISel][TableGen][LoongArch] Report error for trivial bitcasts when there are predicate calls (#116075)

On loongarch64 with lsx extension, we select `VBITREV_W` for `v4i32 (xor
X, (shl splat(1), Y))`:

https://github.com/llvm/llvm-project/blob/8e6630391699116641cf390a10476295b7d4b95c/llvm/lib/Target/LoongArch/LoongArchLSXInstrInfo.td#L1583-L1584

And `vsplat_imm_eq_1` is defined as:

https://github.com/llvm/llvm-project/blob/8e6630391699116641cf390a10476295b7d4b95c/llvm/lib/Target/LoongArch/LoongArchLSXInstrInfo.td#L77-L87

For the `(bitconvert (v4i32 (build_vector)))` case, the pattern is
expected to be:
```
PATTERN: (xor:{ *:[v4i32] } v4i32:{ *:[v4i32] }:$vj, (shl:{ *:[v4i32] } (bitconvert:{ *:[v4i32] } (build_vector:{ *:[v4i32] }))<<P:Predicate_vsplat_imm_eq_1>>, v4i32:{ *:[v4i32] }:$vk))
RESULT:  (VBITREV_W:{ *:[v4i32] } v4i32:{ *:[v4i32] }:$vj, v4i32:{ *:[v4i32] }:$vk)
```

However, `simplifyTree` drops the `bitconvert` node and its predicates:

https://github.com/llvm/llvm-project/blob/8e6630391699116641cf390a10476295b7d4b95c/llvm/utils/TableGen/Common/CodeGenDAGPatterns.cpp#L3036-L3062

Then llvm will match `vsplat_imm_eq_1` for any v4i32 splats and cause a
miscompilation:
```
PATTERN: (xor:{ *:[v4i32] } v4i32:{ *:[v4i32] }:$vj, (shl:{ *:[v4i32] } (build_vector:{ *:[v4i32] }), v4i32:{ *:[v4i32] }:$vk))
RESULT:  (VBITREV_W:{ *:[v4i32] } v4i32:{ *:[v4i32] }:$vj, v4i32:{ *:[v4i32] }:$vk)
```

This patch adds additional checks for predicates associated with the
trivial bitconvert node. Unused patterns in the LoongArch target are
also removed.

Fixes https://github.com/llvm/llvm-project/issues/116008.



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