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Which docs are you looking at? Looking at my copy of the v7-A/R ARM ARM (DDI 0406B) it only lists a v6 (v6 for ARM, v6T2 for Thumb) and v7 encoding for the SMLSD (section A8.6.172). The instruction doesn't appear in my old printed copy of the v5TE ARM ARM.
What version of the tools are you using?