to_cast is not always talloced #7373

Job	Run time
pre-ci	9s
master-self-ubuntu20-linux-gcc-lean	5m 26s
master-self-ubuntu20-linux-gcc	5m 54s
master-self-ubuntu20-linux-gcc-O2-g3	6m 9s
master-self-ubuntu20-linux-gcc-ndebug	5m 48s
master-self-ubuntu20-linux-clang-lean	5m 50s
master-self-ubuntu20-linux-clang	5m 21s
master-self-ubuntu20-linux-clang-O2-g3	5m 50s
master-self-ubuntu20-linux-clang-ndebug	5m 26s
master-self-ubuntu20-linux-clang-altlibs	5m 41s
master-self-ubuntu20-linux-fuzzer	11m 19s
Merge preflight	0s
Merge into upstream	0s
	1h 2m 53s

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