SCCP currently stores instructions whose lattice value has changed in a worklist, and then updates their users in the main loop. This may result in instructions unnecessarily being visited multiple times (as an instruction will often use multiple other instructions). Additionally, we'd often redundantly visit instructions that were already visited when the containing block first became executable. Instead, change the worklist to directly store the instructions that need to be revisited. Additionally, do not add instructions to the worklist that will already be covered by the main basic block walk. This change is conceptually NFC, but is expected to produce minor differences in practice, because the visitation order interacts with the range widening limit.
Currently predicates are allocated on the heap and tracked with an intrusive list. Use a bump pointer allocator instead, which is more efficient. The list is no longer needed, as we don't have to track predicates for freeing. The bump pointer allocator is provided as a parameter for PredicateInfo to allow reusing the same allocator for all functions during IPSCCP.
Do the cheap intrinsic check before the hash lookup for the PredicateInfo.
So it can be reused between IPSCCP and SCCP. Make the implementation a bit more efficient by only lookup the PredicateInfo once.
Following the work in PR #107279, this patch applies the annotative DebugLocs, which indicate that a particular instruction is intentionally missing a location for a given reason, to existing sites in the compiler where their conditions apply. This is NFC in ordinary LLVM builds (each function `DebugLoc::getFoo()` is inlined as `DebugLoc()`), but marks the instruction in coverage-tracking builds so that it will be ignored by Debugify, allowing only real errors to be reported. From a developer standpoint, it also communicates the intentionality and reason for a missing DebugLoc. Some notes for reviewers: - The difference between `I->dropLocation()` and `I->setDebugLoc(DebugLoc::getDropped())` is that the former _may_ decide to keep some debug info alive, while the latter will always be empty; in this patch, I always used the latter (even if the former could technically be correct), because the former could result in some (barely) different output, and I'd prefer to keep this patch purely NFC. - I've generally documented the uses of `DebugLoc::getUnknown()`, with the exception of the vectorizers - in summary, they are a huge cause of dropped source locations, and I don't have the time or the domain knowledge currently to solve that, so I've plastered it all over them as a form of "fixme".
CVP version: https://github.com/llvm/llvm-project/commit/2d5820cd72255e04aaef2da3c21d62396fdd7fb9 Compile-time impact: https://llvm-compile-time-tracker.com/compare.php?from=3ec0c5c7fef03985b43432c6b914c289d8a5435e&to=92b4df90695dd37defdabf8a30f0b0322b648a00&stat=instructions:u
This patch makes getMRVFunctionsTracked return a reference. runIPSCCP, the sole user of getMRVFunctionsTracked, just needs a read-access to the map. The missing "&" is most likely an oversight as two "sibling" functions getTrackedRetVals and getTrackedGlobals return maps by const reference.
try_emplace can default-construct values, so we do not need to do so on our own. Plus, try_emplace(Key) is much shorter than insert(std::make_pair(Key, Value()).