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df7e45dd98
I think currently isImpliedViaMerge can incorrectly return true for phis in a loop/cycle, if the found condition involves the previous value of Consider the case in exit_cond_depends_on_inner_loop. At some point, we call (modulo simplifications) isImpliedViaMerge(<=, %x.lcssa, -1, %call, -1). The existing code tries to prove IncV <= -1 for all incoming values InvV using the found condition (%call <= -1). At the moment this succeeds, but only because it does not compare the same runtime value. The found condition checks the value of the last iteration, but the incoming value is from the *previous* iteration. Hence we incorrectly determine that the *previous* value was <= -1, which may not be true. I think we need to be more careful when looking at the incoming values here. In particular, we need to rule out that a found condition refers to any value that may refer to one of the previous iterations. I'm not sure there's a reliable way to do so (that also works of irreducible control flow). So for now this patch adds an additional requirement that the incoming value must properly dominate the phi block. This should ensure the values do not change in a cycle. I am not entirely sure if will catch all cases and I appreciate a through second look in that regard. Alternatively we could also unconditionally bail out in this case, instead of checking the incoming values Reviewed By: nikic Differential Revision: https://reviews.llvm.org/D101829 |
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| .. | ||
| models/inliner | ||
| AliasAnalysis.cpp | ||
| AliasAnalysisEvaluator.cpp | ||
| AliasAnalysisSummary.cpp | ||
| AliasAnalysisSummary.h | ||
| AliasSetTracker.cpp | ||
| Analysis.cpp | ||
| AssumeBundleQueries.cpp | ||
| AssumptionCache.cpp | ||
| BasicAliasAnalysis.cpp | ||
| BlockFrequencyInfo.cpp | ||
| BlockFrequencyInfoImpl.cpp | ||
| BranchProbabilityInfo.cpp | ||
| CallGraph.cpp | ||
| CallGraphSCCPass.cpp | ||
| CallPrinter.cpp | ||
| CaptureTracking.cpp | ||
| CFG.cpp | ||
| CFGPrinter.cpp | ||
| CFLAndersAliasAnalysis.cpp | ||
| CFLGraph.h | ||
| CFLSteensAliasAnalysis.cpp | ||
| CGSCCPassManager.cpp | ||
| CMakeLists.txt | ||
| CmpInstAnalysis.cpp | ||
| CodeMetrics.cpp | ||
| ConstantFolding.cpp | ||
| ConstraintSystem.cpp | ||
| CostModel.cpp | ||
| DDG.cpp | ||
| DDGPrinter.cpp | ||
| Delinearization.cpp | ||
| DemandedBits.cpp | ||
| DependenceAnalysis.cpp | ||
| DependenceGraphBuilder.cpp | ||
| DevelopmentModeInlineAdvisor.cpp | ||
| DivergenceAnalysis.cpp | ||
| DominanceFrontier.cpp | ||
| DomPrinter.cpp | ||
| DomTreeUpdater.cpp | ||
| EHPersonalities.cpp | ||
| FunctionPropertiesAnalysis.cpp | ||
| GlobalsModRef.cpp | ||
| GuardUtils.cpp | ||
| HeatUtils.cpp | ||
| ImportedFunctionsInliningStatistics.cpp | ||
| IndirectCallPromotionAnalysis.cpp | ||
| InlineAdvisor.cpp | ||
| InlineCost.cpp | ||
| InlineSizeEstimatorAnalysis.cpp | ||
| InstCount.cpp | ||
| InstructionPrecedenceTracking.cpp | ||
| InstructionSimplify.cpp | ||
| Interval.cpp | ||
| IntervalPartition.cpp | ||
| IRSimilarityIdentifier.cpp | ||
| IVDescriptors.cpp | ||
| IVUsers.cpp | ||
| LazyBlockFrequencyInfo.cpp | ||
| LazyBranchProbabilityInfo.cpp | ||
| LazyCallGraph.cpp | ||
| LazyValueInfo.cpp | ||
| LegacyDivergenceAnalysis.cpp | ||
| Lint.cpp | ||
| Loads.cpp | ||
| LoopAccessAnalysis.cpp | ||
| LoopAnalysisManager.cpp | ||
| LoopCacheAnalysis.cpp | ||
| LoopInfo.cpp | ||
| LoopNestAnalysis.cpp | ||
| LoopPass.cpp | ||
| LoopUnrollAnalyzer.cpp | ||
| MemDepPrinter.cpp | ||
| MemDerefPrinter.cpp | ||
| MemoryBuiltins.cpp | ||
| MemoryDependenceAnalysis.cpp | ||
| MemoryLocation.cpp | ||
| MemorySSA.cpp | ||
| MemorySSAUpdater.cpp | ||
| MLInlineAdvisor.cpp | ||
| ModuleDebugInfoPrinter.cpp | ||
| ModuleSummaryAnalysis.cpp | ||
| MustExecute.cpp | ||
| ObjCARCAliasAnalysis.cpp | ||
| ObjCARCAnalysisUtils.cpp | ||
| ObjCARCInstKind.cpp | ||
| OptimizationRemarkEmitter.cpp | ||
| OverflowInstAnalysis.cpp | ||
| PHITransAddr.cpp | ||
| PhiValues.cpp | ||
| PostDominators.cpp | ||
| ProfileSummaryInfo.cpp | ||
| PtrUseVisitor.cpp | ||
| README.txt | ||
| RegionInfo.cpp | ||
| RegionPass.cpp | ||
| RegionPrinter.cpp | ||
| ReleaseModeModelRunner.cpp | ||
| ReplayInlineAdvisor.cpp | ||
| ScalarEvolution.cpp | ||
| ScalarEvolutionAliasAnalysis.cpp | ||
| ScalarEvolutionDivision.cpp | ||
| ScalarEvolutionNormalization.cpp | ||
| ScopedNoAliasAA.cpp | ||
| StackLifetime.cpp | ||
| StackSafetyAnalysis.cpp | ||
| StratifiedSets.h | ||
| SyncDependenceAnalysis.cpp | ||
| SyntheticCountsUtils.cpp | ||
| TargetLibraryInfo.cpp | ||
| TargetTransformInfo.cpp | ||
| TFUtils.cpp | ||
| Trace.cpp | ||
| TypeBasedAliasAnalysis.cpp | ||
| TypeMetadataUtils.cpp | ||
| ValueLattice.cpp | ||
| ValueLatticeUtils.cpp | ||
| ValueTracking.cpp | ||
| VectorUtils.cpp | ||
| VFABIDemangling.cpp | ||
Analysis Opportunities:
//===---------------------------------------------------------------------===//
In test/Transforms/LoopStrengthReduce/quadradic-exit-value.ll, the
ScalarEvolution expression for %r is this:
{1,+,3,+,2}<loop>
Outside the loop, this could be evaluated simply as (%n * %n), however
ScalarEvolution currently evaluates it as
(-2 + (2 * (trunc i65 (((zext i64 (-2 + %n) to i65) * (zext i64 (-1 + %n) to i65)) /u 2) to i64)) + (3 * %n))
In addition to being much more complicated, it involves i65 arithmetic,
which is very inefficient when expanded into code.
//===---------------------------------------------------------------------===//
In formatValue in test/CodeGen/X86/lsr-delayed-fold.ll,
ScalarEvolution is forming this expression:
((trunc i64 (-1 * %arg5) to i32) + (trunc i64 %arg5 to i32) + (-1 * (trunc i64 undef to i32)))
This could be folded to
(-1 * (trunc i64 undef to i32))
//===---------------------------------------------------------------------===//