In Record only store the direct superclasses instead of all
superclasses. getSuperClasses recurses to find all superclasses when
necessary.
This gives a small reduction in memory usage. On lib/Target/X86/X86.td I
measured about 2.0% reduction in total bytes allocated (measured by
valgrind) and 1.3% reduction in peak memory usage (measured by
/usr/bin/time -v).
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Co-authored-by: Min-Yih Hsu <min@myhsu.dev>
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