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a=ul9cdbp4aOFLsgKbc677:22 TL;DR: Thinking and experimenting a bit on the possible approaches for avoiding unaligned accesses in the SFrame FRE layout (in SFrame V3), I am not convinced that avoiding unaligned accesses for performance is worth it. IMO, forsaking compactness for avoiding unaligned accesses is not a good trade off for SFrame. Problem Statement On architectures such as x86_64, AArch64, and s390x, unaligned memory accesses are handled transparently by the hardware but incur a performance penalty. The objective of this analysis is to evaluate if these unaligned accesses can be eliminated from the SFrame FRE layout and if doing so provides a net performance benefit. The central challenge is that any alternative must demonstrate a clear performance improvement while avoiding significant size overhead. Introducing "bloat" to the format to solve a potential performance issue is a poor trade-off. Source of unaligned accesses in SFrame FRE - (#1) Access to the SFrame FRE start address (sfre_start_address) - (#2) Access to the SFrame FRE stack offsets, This is varlen data tailing SFrame FRE top-level members (sfre_start_address and FRE info), usually interpreted as stack offsets) (Note that in the SFrame specification, SFrame Header, and SFrame FDE (function descriptor entry) have aligned accesses.) Updated notes on the various approaches and respective evaluation notes on the wiki page: https://sourceware.org/binutils/wiki/sframe/sframev3todo#Avoid_unaligned_accesses Summary of Approaches and Analysis/Notes Unaligned accesses may mean lower performance, but the alternative we pick must at least provide better performance. It is also important that the chosen approach does not add bloat to the format. Avoiding unaligned accesses at the expense of bloating up the format is not a good idea IMO. Approach 1a: Bucketed members Pros: Negligible bloat. Cons: 1. Writing out the FRE data is somewhat more involved. Affects assemblers, linkers. 2. For the common case though, accessing stack offsets now needs more memory accesses per FRE. This approach will not bring clear performance benefits; the additional complexity in SFrame readers and writers is not justified then either. Approach 1b: Bucketed members with Index Cons: Significant bloat (~30%). Approach 2: De-duplicated "stack offsets" Pros: Will help reduce the size of SFrame sections. Cons: 1. SFrame FRE layout is designed to be flexible so that it can serve needs of new ABIs: The varlen data is interpreted as stack offsets on x86_64, and AArch64, but may not be the case for other ABIs. De-duplicating non-structured data is not meaningful. 2. Writing out the FRE data is quite more involved, increasing the complexity in Toolchain. Approach 3: Good old basic padding Cons: Significant bloat (~22%). Performance win arguable as well. IMO, none of these approaches provide viable way to move forward. The proposed methods either fail to deliver the desired clear performance gain or introduce a significant size penalty or complexity, which is an unacceptable trade-off. Would like to gather inputs from the interested folks on this. Please take a look and chime in. Other ideas welcome. Thanks