From: lkcl Date: Wed, 11 Nov 2020 21:27:32 +0000 (+0000) Subject: (no commit message) X-Git-Tag: convert-csv-opcode-to-binary~1844 X-Git-Url: https://git.libre-soc.org/?a=commitdiff_plain;h=c1b0c8df3bfb2ec3133b8653eab2f066ecf11d7e;p=libreriscv.git --- diff --git a/openpower/sv/predication.mdwn b/openpower/sv/predication.mdwn index 5d7a989ba..7e866414f 100644 --- a/openpower/sv/predication.mdwn +++ b/openpower/sv/predication.mdwn @@ -26,7 +26,7 @@ * 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 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. +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 very simply be directly ANDed with the regfile write-enable lines to achieve the required functionality of leaving masked-out elements unmodified, right down to the 8 bit element level. 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