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...ed familiarity with ScalarEvolution code I would like to propose a solution that may work- Have two levels of caching for data structures for which infinite recursion is possible (like Value -> SCEV, Value->Predicate, Loop->BackedgeTakenCount etc). The first level of caching is the 'PendingCache' and the second one is the 'FinalCache'. PendingCache is similar to PendingLoopPredicates. It is used to break infinite recursion. In addition we keep a Boolean class member 'PessimisticMode' (common to all caches). The lookup logic for the cache is something like this- If (P...

...iedSCEVs.find(AlreadyPresent)) { return Simplified; } return AlreadyPresent; } ... // We discovered zext(s) can be simplified to t UniqueSCEVs.insert({kZeroExtend, S}, t); SimplifiedSCEVs[s] = t; return t; } > The first level of caching is the 'PendingCache' and the second one is the 'FinalCache'. PendingCache is similar to PendingLoopPredicates. It is used to break infinite recursion. In addition we keep a Boolean class member 'PessimisticMode' (common to all caches). > > The lookup logic for the cache is something like this...

...d by the same 'IsTopCall' approach. > > ScalarEvolution::getSCEVImpl (Value *V, bool IsTopCall = false) { > // Look up in cache using logic described above > If (S = getExistingSCEV()) > return S; > > if (IsTopCall) { > PessimisticMode = false; > PendingCache.clear(); > PendingCache.insert(V, getUnknown(V)); >> Can this be assert(!PessimisticMode && !PendingCache.empty()) since on a "top call" we could not have hit self recursion yet? Yes, if we reset them before exiting 'IsTopCall'. I wasn't doing that :)...

...ch. > >> >> ScalarEvolution::getSCEVImpl (Value *V, bool IsTopCall = false) { >> // Look up in cache using logic described above >> If (S = getExistingSCEV()) >> return S; >> >> if (IsTopCall) { >> PessimisticMode = false; >> PendingCache.clear(); >> PendingCache.insert(V, getUnknown(V)); > >>> Can this be assert(!PessimisticMode && !PendingCache.empty()) since on a "top call" we could not have hit self recursion yet? > > > Yes, if we reset them before exiting 'IsTopCall'. I wa...

...d by the same 'IsTopCall' approach. > > ScalarEvolution::getSCEVImpl (Value *V, bool IsTopCall = false) { > // Look up in cache using logic described above > If (S = getExistingSCEV()) > return S; > > if (IsTopCall) { > PessimisticMode = false; > PendingCache.clear(); > PendingCache.insert(V, getUnknown(V)); >> Can this be assert(!PessimisticMode && !PendingCache.empty()) since on a "top call" we could not have hit self recursion yet? Yes, if we reset them before exiting 'IsTopCall'. I wasn't doing that :)...

Hi, +CC Max, Serguei This looks like a textbook case of why caching is hard. We first call getZeroExtendExpr on %dec, and this call does end up returning an add rec. However, in the process of simplifying the zext, it also calls into isLoopBackedgeGuardedByCond which in turn calls getZeroExtendExpr(%dec) again. However, this second (recursive) time, we don't simplify the zext and cache a

...ch. > >> >> ScalarEvolution::getSCEVImpl (Value *V, bool IsTopCall = false) { >> // Look up in cache using logic described above >> If (S = getExistingSCEV()) >> return S; >> >> if (IsTopCall) { >> PessimisticMode = false; >> PendingCache.clear(); >> PendingCache.insert(V, getUnknown(V)); > >>> Can this be assert(!PessimisticMode && !PendingCache.empty()) since on a "top call" we could not have hit self recursion yet? > > > Yes, if we reset them before exiting 'IsTopCall'. I wa...

Hi Sanjoy, SCEV is behaving inconsistently when forming SCEV for this zext instruction in the attached test case- %conv5 = zext i32 %dec to i64 If we request a SCEV for the instruction, it returns- (zext i32 {{-1,+,1}<nw><%for.body>,+,-1}<nw><%for.body7> to i64) This can be seen by invoking- $ opt -analyze -scalar-evolution inconsistent-scev-zext.ll But when computing

...calarEvolution::getSCEVImpl (Value *V, bool IsTopCall = false) { >>> // Look up in cache using logic described above >>> If (S = getExistingSCEV()) >>> return S; >>> >>> if (IsTopCall) { >>> PessimisticMode = false; >>> PendingCache.clear(); >>> PendingCache.insert(V, getUnknown(V)); >> >>>> Can this be assert(!PessimisticMode && !PendingCache.empty()) since on a "top call" we could not have hit self recursion yet? >> >> >> Yes, if we reset them before exiting &...