From: lkcl Date: Sat, 28 Aug 2021 10:49:28 +0000 (+0100) Subject: (no commit message) X-Git-Tag: DRAFT_SVP64_0_1~288 X-Git-Url: https://git.libre-soc.org/?a=commitdiff_plain;h=67c6defe948b699eabd2814bb6c9e7e75ef1a5be;p=libreriscv.git --- diff --git a/openpower/sv/svp64/appendix.mdwn b/openpower/sv/svp64/appendix.mdwn index d374baa50..ce1765351 100644 --- a/openpower/sv/svp64/appendix.mdwn +++ b/openpower/sv/svp64/appendix.mdwn @@ -390,9 +390,12 @@ executed in sequential Program Order, element 0 being the first. CR-creating operation produces a result (including cmp). Similar to branch, an analysis of the CR is performed and if the test fails, the vector operation terminates and discards all element operations at and - above the current one, and VL is truncated to the *previous* element. - Thus the new VL comprises a contiguous vector of results, all of which - pass the testing criteria (equal to zero, less than zero). + above the current one, and VL is truncated to either + the *previous* element or the current one, depending on whether + VLi (VL "inclusive") is set. + +Thus the new VL comprises a contiguous vector of results, +all of which pass the testing criteria (equal to zero, less than zero). The CR-based data-driven fail-on-first is new and not found in ARM SVE or RVV. It is extremely useful for reducing instruction count, @@ -405,6 +408,13 @@ If the CR.eq bit is equal to `inv` then the Vector is truncated and the loop ends. Note that when RC1=1 the result elements are never stored, only the CRs. +VLi is only available as an option when `Rc=0` (or for instructions +which do not have Rc). When set, the current element is always +also included in the count (the new length that VL will be set to). +This may be useful in combination with "inv" to truncate the Vector +to `exclude` elements that fail a test, or, in the case of implementations +of strncpy, to include the terminating zero. + In CR-based data-driven fail-on-first there is only the option to select and test one bit of each CR (just as with branch BO). For more complex tests this may be insufficient. If that is the case, a vectorised crops