Fix x86 SSE4.1 ptestnzc #3216
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Fix x86 SSE4.1 ptestnzc #3216
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`(op & mask) == 0` and `(op & mask) == mask` need each to be calculated for the whole vector. For example, given * `op = [0b100, 0b010]` * `mask = [0b100, 0b110]` The correct result would be: * `op & mask = [0b100, 0b010]` Comparisons are done on the vector as a whole: * `all_zero = (op & mask) == [0, 0] = false` * `masked_set = (op & mask) == mask = false` * `!all_zero && !masked_set = true` The previous method: `op & mask = [0b100, 0b010]` Comparisons are done element-wise: * `all_zero = (op & mask) == [0, 0] = [true, true]` * `masked_set = (op & mask) == mask = [true, false]` * `!all_zero && !masked_set = [true, false]` After folding with AND, the final result would be `false`, which is incorrect.
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Ah... unfortunate. I guess we could still express this as a fold if we wanted (by folding over a pair of booleans), but it doesn't seem worth it. @bors r+ |
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Fixes ptestnzc by bringing back the original implementation of #3214.
(op & mask) != 0 && (op & mask) == !askneed to be calculated for the whole vector. It cannot be calculated for each element and then folded.For example, given
op = [0b100, 0b010]mask = [0b100, 0b110]The correct result would be:
op & mask = [0b100, 0b010]Comparisons are done on the vector as a whole:
all_zero = (op & mask) == [0, 0] = falsemasked_set = (op & mask) == mask = false!all_zero && !masked_set = truecorrect resultThe previous method:
op & mask = [0b100, 0b010]Comparisons are done element-wise:
all_zero = (op & mask) == [0, 0] = [true, true]masked_set = (op & mask) == mask = [true, false]!all_zero && !masked_set = [true, false]After folding with AND, the final result would be
false, which is incorrect.