[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.

1 files changed, 8 insertions, 0 deletions

diff --git a/llvm/utils/TableGen/Common/CodeGenDAGPatterns.cpp b/llvm/utils/TableGen/Common/CodeGenDAGPatterns.cpp
index c8186d6..163a1a7 100644
--- a/llvm/utils/TableGen/Common/CodeGenDAGPatterns.cpp
+++ b/llvm/utils/TableGen/Common/CodeGenDAGPatterns.cpp
@@ -3056,6 +3056,14 @@ static bool SimplifyTree(TreePatternNodePtr &N) {
       !N->getExtType(0).empty() &&
       N->getExtType(0) == N->getChild(0).getExtType(0) &&
       N->getName().empty()) {
+    if (!N->getPredicateCalls().empty()) {
+      std::string Str;
+      raw_string_ostream OS(Str);
+      OS << *N
+         << "\n trivial bitconvert node should not have predicate calls\n";
+      PrintFatalError(Str);
+      return false;
+    }
     N = N->getChildShared(0);
     SimplifyTree(N);
     return true;