Artem-B wrote: The description of the flat address space in the `TargetTransformInfo.h` is somewhat vague and both, soo specific and not precise enough, IMO: ``` The flat address space is a /// generic address space that can be used access multiple segments of memory /// with different address spaces. Access of a memory location through a /// pointer with this address space is expected to be legal but slower /// compared to the same memory location accessed through a pointer with a /// different address space. /// /// This is for targets with different pointer representations which can /// be converted with the addrspacecast instruction. If a pointer is converted /// to this address space, optimizations should attempt to replace the access /// with the source address space. ```
- "can be used access multiple segments of memory with different AS" -- does it mean all of them? If it covers only some of the segments, which ones? - "access expected to be slower" -- that's also not necessarily a universal property. It's conceivable that on some architectures, it's conversion between address spaces that may be non-free, but once you have the pointer, actual accesses work equally fast. > * Can there be more than one flat address space? > - No Why not? E.g. if we have a processor with Harvard architecture, there may conceivably be multiple 'flat', non-overlapping address spaces, each covering a set of specific ASes. I think conceptually we should describe AS hierarchy explicitly, and avoid the assumptions on their number or layout. E.g. `T0:1,2,3,4,5` may mean `AS 0` is a flat superset of `AS 1,2,3,4,5`. ... and then change the API to `getParentAS(AS)` which would return AS itself if it's not contained in any other AS, or the higher level AS. https://github.com/llvm/llvm-project/pull/108786 _______________________________________________ cfe-commits mailing list cfe-commits@lists.llvm.org https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
