From: lkcl Date: Mon, 26 Oct 2020 22:41:15 +0000 (+0000) Subject: (no commit message) X-Git-Tag: convert-csv-opcode-to-binary~1922 X-Git-Url: https://git.libre-soc.org/?a=commitdiff_plain;h=e72076699ae8486fbbd8efb4a18800e6bbee9a23;hp=e1f783c7326a8ca8f62870f4c60a373af949f695;p=libreriscv.git --- diff --git a/openpower/sv/predication.mdwn b/openpower/sv/predication.mdwn index d3c722798..c4bc0897f 100644 --- a/openpower/sv/predication.mdwn +++ b/openpower/sv/predication.mdwn @@ -25,7 +25,7 @@ * two modes, "zeroing" and "non-zeroing". zeroing mode places a zero in the masked-out element results, where non-zeroing leaves the destination (result) element unmodified. * predicate must be invertable via an opcode bit (to avoid the need for an instruction which inverts all bits of the predicate mask) -Implementation note: even in in-order microarchitectures it is strongly adviseable to use byte-level write-enable lines on the register file. This in combination with 8-bit SIMD element overrides allows, in "non-zeroing" mode, the predicate mask to be directly ANDed with the regfile write-enable lines to achieve the required functionality. The alternative is to perform a READ-MODIFY-MASK-WRITE cycle which is costly and compromises performance. Avoided very simply with byte-level write-enable. +Implementation note: even in in-order microarchitectures it is strongly adviseable to use byte-level write-enable lines on the register file. This in combination with 8-bit SIMD element overrides allows, in "non-zeroing" mode, the predicate mask can very simply be directly ANDed with the regfile write-enable lines to achieve the required functionality of leaving masked-out elements unmodified. The alternative is to perform a READ-MODIFY-MASK-WRITE cycle which is costly and compromises performance. Avoided very simply with byte-level write-enable. ## General implications and considerations