From 6b1c68a92f1f6beb901176b845c2bb09d2b3a6c8 Mon Sep 17 00:00:00 2001 From: lkcl Date: Sun, 2 Apr 2023 20:42:43 +0100 Subject: [PATCH] --- openpower/sv/ldst.mdwn | 24 ++++++++++++++++++------ 1 file changed, 18 insertions(+), 6 deletions(-) diff --git a/openpower/sv/ldst.mdwn b/openpower/sv/ldst.mdwn index eabb471b1..92521b0ec 100644 --- a/openpower/sv/ldst.mdwn +++ b/openpower/sv/ldst.mdwn @@ -70,7 +70,7 @@ alternative table definition for [[sv/svp64]] `RM.MODE`. The following modes make sense: * saturation -* predicate-result (mostly for cache-inhibited LD/ST) +* predicate-result would be useful but is lower priority than Data-Dependent Fail-First * simple (no augmentation) * fail-first (where Vector Indexed is banned) * Signed Effective Address computation (Vector Indexed only) @@ -82,8 +82,7 @@ of space, have the following quirks: * LD/ST Immediate has no individual control over src/dest zeroing, whereas LD/ST Indexed does. -* LD/ST Indexed has limited zeroing on pred-result, LD/ST Immediate has - *no* option to select zeroing on pred-result. +* LD/ST Immediate has saturation but LD/ST Indexed does not. ## Format and fields @@ -104,6 +103,12 @@ Fields used in tables below: EA is stored in RA **after** it is actually used. * **LF** - Load/Store Fail or Fault First: for any reason Load or Store Vectors may be truncated to (at least) one element, and VL altered to indicate such. +* **VLi* - Inclusive Data-Dependent Fail-First: the failing element is included + in the Truncated Vector. + +When VLi=0 on Store Operations the Memory update does **not** take place +on the element that failed. EA does **not** update into RA on Load/Store +with Update instructions either. **LD/ST immediate** @@ -456,10 +461,17 @@ when VLi is clear, must all pass the "test", but when VLi is set the update (store) to Memory is **not permitted to take place** should the test fail. Therefore, on testing the value to be stored, and after updating the corresponding CR Field Element, when VLi=0 and finding that the -test fails the Memory store must **not** occur. By contrast if VLi=1 -and the test the Store may proceed *and then* looping terminates. +test fails the Memory store must **not** occur. + +Additionally, when VLi=0 and a test fails then RA does **not** receive a +copy of the Effective Address. Hardware implementations with Out-of-Order +Micro-Architectures should use speculative Shadow-Hold and Cancellation +when the test fails. + +By contrast if VLi=1 +and the test fails, Store may proceed *and then* looping terminates. In this way, when non-Inclusive, the Vector of Truncated results contains -only Stores that passed the test, and when Inclusive the Vector of +only Stores that passed the test (and RA=EA updates if any), and when Inclusive the Vector of Truncated results contains the first-failed data. Below is an example of loading the starting addresses of Linked-List nodes. -- 2.30.2