fallback: buffer related fixes #3275

Job	Run time
macOS / release / homebrew-clang	5m 34s
macOS / debug / homebrew-clang	4m 59s
macOS / release / system-clang	4m 15s
macOS / debug / system-clang	3m 53s
Windows / release / msvc	29m 21s
Windows / release / clang-cl	24m 11s
Windows / release / llvm	15m 59s
Windows / debug / msvc	17m 10s
Windows / debug / clang-cl	18m 44s
Windows / debug / llvm	20m 7s
	2h 24m 13s

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