In general, count-zeros instructions are undefined for a zero input value. However the X86 TZCNT and LZCNT instructions do return the bit-width on a zero input, so make Clang tell LLVM so. One quirk is that these instructions aren't necessarily both defined, so also create a separate predicate so we can do the right thing for all CPUs. --paulr
ctz-clz.diff
Description: ctz-clz.diff
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