[AArch64] Add missing bf16 store pattern (#72844)

We have STURHi store patterns but would fail to select from unscaled
offsets. This adds the missing pattern.

Author: erickq

llvm/lib/Target/AArch64/AArch64InstrInfo.td

@@ -3926,6 +3926,11 @@ defm STURBB : StoreUnscaled<0b00, 0, 0b00, GPR32z, "sturb",
                          [(truncstorei8 GPR32z:$Rt,
                                   (am_unscaled8 GPR64sp:$Rn, simm9:$offset))]>;
 
+// bf16 store pattern
+def : Pat<(store (bf16 FPR16Op:$Rt),
+                 (am_unscaled16 GPR64sp:$Rn, simm9:$offset)),
+          (STURHi FPR16:$Rt, GPR64sp:$Rn, simm9:$offset)>;
+
 // Armv8.4 Weaker Release Consistency enhancements
 //         LDAPR & STLR with Immediate Offset instructions
 let Predicates = [HasRCPC_IMMO] in {

llvm/test/CodeGen/AArch64/bf16.ll

@@ -45,6 +45,16 @@ define void @test_store(ptr %a, bfloat %b) nounwind {
   ret void
 }
 
+define void @test_store_negative_offset(ptr %a, bfloat %b) nounwind {
+; CHECK-LABEL: test_store_negative_offset:
+; CHECK-NEXT: stur    h0, [x0, #-4]
+; CHECK-NEXT: ret
+entry:
+  %0 = getelementptr inbounds bfloat, ptr %a, i64 -2
+  store bfloat %b, ptr %0, align 2
+  ret void
+}
+
 ; Simple store of v4bf16
 define void @test_vec_store(ptr %a, <4 x bfloat> %b) nounwind {
 ; CHECK-LABEL: test_vec_store: