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([2607:fea8:a263:f600::3dbe]) by smtp.gmail.com with ESMTPSA id cb24-20020a05622a1f9800b0034355a352d1sm12164725qtb.92.2022.10.04.08.42.33 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 04 Oct 2022 08:42:33 -0700 (PDT) Message-ID: <974d3399-7eac-803d-2c64-fb7d7bf3f71f@redhat.com> Date: Tue, 4 Oct 2022 11:42:32 -0400 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.2.1 Subject: Re: [COMMITTED] Convert nonzero mask in irange to wide_int. To: Aldy Hernandez , Richard Biener Cc: GCC patches References: <07FCA378-7E86-4E06-B506-FED0C60CE31C@gmail.com> From: Andrew MacLeod In-Reply-To: X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Spam-Status: No, score=-7.6 required=5.0 tests=BAYES_00,DKIMWL_WL_HIGH,DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,NICE_REPLY_A,RCVD_IN_DNSWL_NONE,SPF_HELO_NONE,SPF_NONE,TXREP autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on server2.sourceware.org List-Id: On 10/4/22 11:14, Aldy Hernandez wrote: > On Tue, Oct 4, 2022 at 4:34 PM Richard Biener > wrote: >> >> >>> Am 04.10.2022 um 16:30 schrieb Aldy Hernandez : >>> >>> On Tue, Oct 4, 2022 at 3:27 PM Andrew MacLeod wrote: >>>> >>>>> On 10/4/22 08:13, Aldy Hernandez via Gcc-patches wrote: >>>>>> On Tue, Oct 4, 2022, 13:28 Aldy Hernandez wrote: >>>>>> On Tue, Oct 4, 2022 at 9:55 AM Richard Biener >>>>>> wrote: >>>>>>> Am 04.10.2022 um 09:36 schrieb Aldy Hernandez via Gcc-patches < >>>>>> gcc-patches@gcc.gnu.org>: >>>>>>>> The reason the nonzero mask was kept in a tree was basically inertia, >>>>>>>> as everything in irange is a tree. However, there's no need to keep >>>>>>>> it in a tree, as the conversions to and from wide ints are very >>>>>>>> annoying. That, plus special casing NULL masks to be -1 is prone >>>>>>>> to error. >>>>>>>> >>>>>>>> I have not only rewritten all the uses to assume a wide int, but >>>>>>>> have corrected a few places where we weren't propagating the masks, or >>>>>>>> rather pessimizing them to -1. This will become more important in >>>>>>>> upcoming patches where we make better use of the masks. >>>>>>>> >>>>>>>> Performance testing shows a trivial improvement in VRP, as things like >>>>>>>> irange::contains_p() are tied to a tree. Ughh, can't wait for trees in >>>>>>>> iranges to go away. >>>>>>> You want trailing wide int storage though. A wide_int is quite large. >>>>>> Absolutely, this is only for short term storage. Any time we need >>>>>> long term storage, say global ranges in SSA_NAME_RANGE_INFO, we go >>>>>> through vrange_storage which will stream things in a more memory >>>>>> efficient manner. For irange, vrange_storage will stream all the >>>>>> sub-ranges, including the nonzero bitmask which is the first entry in >>>>>> such storage, as trailing_wide_ints. >>>>>> >>>>>> See irange_storage_slot to see how it lives in GC memory. >>>>>> >>>>> That being said, the ranger's internal cache uses iranges, albeit with a >>>>> squished down number of subranges (the minimum amount to represent the >>>>> range). So each cache entry will now be bigger by the difference between >>>>> one tree and one wide int. >>>>> >>>>> I wonder if we should change the cache to use vrange_storage. If not now, >>>>> then when we convert all the subranges to wide ints. >>>>> >>>>> Of course, the memory pressure of the cache is not nearly as problematic as >>>>> SSA_NAME_RANGE_INFO. The cache only stores names it cares about. >>>> Rangers cache can be a memory bottleneck in pathological cases.. >>>> Certainly not as bad as it use to be, but I'm sure it can still be >>>> problematic. Its suppose to be a memory efficient representation >>>> because of that. The cache can have an entry for any live ssa-name >>>> (which means all of them at some point in the IL) multiplied by a factor >>>> involving the number of dominator blocks and outgoing edges ranges are >>>> calculated on. So while SSA_NAME_RANGE_INFO is a linear thing, the >>>> cache lies somewhere between a logarithmic and exponential factor based >>>> on the CFG size. >>> Hmmm, perhaps the ultimate goal here should be to convert the cache to >>> use vrange_storage, which uses trailing wide ints for all of the end >>> points plus the masks (known_ones included for the next release). >>> >>>> if you are growing the common cases of 1 to 2 endpoints to more than >>>> double in size (and most of the time not be needed), that would not be >>>> very appealing :-P If we have any wide-ints, they would need to be a >>>> memory efficient version. The Cache uses an irange_allocator, which is >>>> suppose to provide a memory efficient objects.. hence why it trims the >>>> number of ranges down to only what is needed. It seems like a trailing >>>> wide-Int might be in order based on that.. >>>> >>>> Andrew >>>> >>>> >>>> PS. which will be more problematic if you eventually introduce a >>>> known_ones wide_int. I thought the mask tracking was/could be >>>> something simple like HOST_WIDE_INT.. then you only tracks masks in >>>> types up to the size of a HOST_WIDE_INT. then storage and masking is >>>> all trivial without going thru a wide_int. Is that not so/possible? >>> That's certainly easy and cheaper to do. The hard part was fixing all >>> the places where we weren't keeping the masks up to date, and that's >>> done (sans any bugs ;-)). >>> >>> Can we get consensus here on only tracking masks for type sizes less >>> than HOST_WIDE_INT? I'd hate to do all the work only to realize we >>> need to track 512 bit masks on a 32-bit host cross :-). >> 64bits are not enough, 128 might be. But there’s trailing wide int storage so I don’t see the point in restricting ourselves? > Fair enough. Perhaps we should bite the bullet and convert the cache > to vrange_storage which is all set up for streaming irange's with > trailing_wide_ints. No changes should be necessary for irange, since > we never have more than 3-4 live at any one time. It's the cache that > needs twiddling. > Wouldnt it be irange_allocator that needs twiddling?  It purpose in life is to allocate iranges for memory storage...  the cache is just a client, as is rangers global cache, etc...  that was the intention of irange_allocator to isolate clients from having to worry about memory storage issues? Or is that problematic? Andrew