From: lkcl Date: Sun, 18 Sep 2022 11:00:14 +0000 (+0100) Subject: (no commit message) X-Git-Tag: opf_rfc_ls005_v1~374 X-Git-Url: https://git.libre-soc.org/?a=commitdiff_plain;h=2c6e5b01930d0f5f1dbd30b8e33e78ef0e7b7a73;p=libreriscv.git --- diff --git a/openpower/sv/rfc/ls001.mdwn b/openpower/sv/rfc/ls001.mdwn index b8c860b25..8b510c2d8 100644 --- a/openpower/sv/rfc/ls001.mdwn +++ b/openpower/sv/rfc/ls001.mdwn @@ -423,15 +423,16 @@ much more powerful with the operations, and secondly by adding powerful binary and ternary CR Field operations into the bitmanip extension.[^crops] -On top of these additional instructions, RM Modes may still be applied, particularly mapreduce and Data-Dependent Fail-first. The usefulness of +On these instructions RM Modes may still be applied (mapreduce and Data-Dependent Fail-first). The usefulness of being able to auto-truncate subsequent Vector Processing at the point -at which a CR Field test fails should be very clear. - -With element-width overrides being meaningless for CR Fields the -decision to use those bits in RM for other purposes was an easy one. -This does provide more uniformity and flexibility to CR Field -operations, but there are less options: neither Saturation nor -Predicate-Result make sense. +at which a CR Field test fails, based on any arbitary logical operation involving `three` CR Field Vectors (`crternlogi`) should be clear, as +should the benefits of being able to do mapreduce and REMAP Parallel +Reduction on `crternlogi`: dramatic reduction in instruction count +for Branch-based control flow when faced with complex analysis of +multiple Vectors. + +Overall the addition of the CR Operations and the CR RM Modes is about +getting instruction count down and increasing the power and flexibility of CR Fields as pressed into service for the purpose of Predicate Masks. [^crops]: the alternative to powerful transfer instructions between GPR and CR Fields was to add the full duplicated suite of BMI and TBM operations present in GPR (popcnt, cntlz, set-before-first) as CR Field Operations. all of which was deemed inappropriate.