[llvm] [SelectionDAG] Preserve volatile undef stores. (PR #99918)

[Matt Arsenault via llvm-commits]

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@@ -90,3 +90,19 @@ define void @test_store_def(i64 %param0, i32 %param1, ptr %out) {
   store %struct.T %S2, ptr %out
   ret void
 }
+
+define void @test_store_volatile_undef(ptr %out) {
+; CHECK-LABEL: test_store_volatile_undef(
+; CHECK:       {
+; CHECK-NEXT:    .reg .b32 %r<7>;
+; CHECK-NEXT:    .reg .b64 %rd<3>;
+; CHECK-EMPTY:
+; CHECK-NEXT:  // %bb.0:
+; CHECK-NEXT:    ld.param.u64 %rd1, [test_store_volatile_undef_param_0];
+; CHECK-NEXT:    st.volatile.v4.u32 [%rd1+16], {%r1, %r2, %r3, %r4};
+; CHECK-NEXT:    st.volatile.v2.u32 [%rd1+8], {%r5, %r6};
+; CHECK-NEXT:    st.volatile.u64 [%rd1], %rd2;
+; CHECK-NEXT:    ret;
+  store volatile %struct.T undef, ptr %out
+  ret void
+}
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arsenm wrote:

Specifically a vector that requires legalization splitting 

https://github.com/llvm/llvm-project/pull/99918