[llvm] [LLVM][CodeGen][SVE] Use BFMLALB for promoted bfloat fma operations. (PR #167340)

[Benjamin Maxwell via llvm-commits]

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@@ -2578,6 +2578,10 @@ let Predicates = [HasBF16, HasSVE_or_SME] in {
   defm BFMLALB_ZZZI : sve2_fp_mla_long_by_indexed_elem<0b100, "bfmlalb", nxv4f32, nxv8bf16, int_aarch64_sve_bfmlalb_lane_v2>;
   defm BFMLALT_ZZZI : sve2_fp_mla_long_by_indexed_elem<0b101, "bfmlalt", nxv4f32, nxv8bf16, int_aarch64_sve_bfmlalt_lane_v2>;
 
+  def : Pat<(nxv4f32 (AArch64fmla_p (SVEAllActive), nxv4f32:$acc, (nxv4f32 (AArch64fcvte_mt (SVEAllActive), nxv4bf16:$Zn, (undef))),
+                                                                  (nxv4f32 (AArch64fcvte_mt (SVEAllActive), nxv4bf16:$Zm, (undef))))),
+            (BFMLALB_ZZZ nxv4f32:$acc, ZPR:$Zn, ZPR:$Zm)>;
----------------
MacDue wrote:

nit: Can you line wrap this, it's hard to read on GitHub:
```suggestion
  def : Pat<(nxv4f32 (AArch64fmla_p (SVEAllActive), nxv4f32:$acc, 
              (nxv4f32 (AArch64fcvte_mt (SVEAllActive), nxv4bf16:$Zn, (undef))),
              (nxv4f32 (AArch64fcvte_mt (SVEAllActive), nxv4bf16:$Zm, (undef))))),
            (BFMLALB_ZZZ nxv4f32:$acc, ZPR:$Zn, ZPR:$Zm)>;
```

https://github.com/llvm/llvm-project/pull/167340