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068181fb4a
This patch extends applyLoopGuards to detect a single-cond range check
idiom that InstCombine generates.
It extends applyLoopGuards to detect conditions of the form
(-C1 + X < C2). InstCombine will create this form when combining two
checks of the form (X u< C2 + C1) and (X >=u C1).
In practice, this enables us to correctly compute a tight trip count
bounds for code as in the function below. InstCombine will fold the
minimum iteration check created by LoopRotate with the user check (< 8).
void unsigned_check(short *pred, unsigned width) {
if (width < 8) {
for (int x = 0; x < width; x++)
pred[x] = pred[x] * pred[x];
}
}
As a consequence, LLVM creates dead vector loops for the code above,
e.g. see https://godbolt.org/z/cb8eTcqET
https://alive2.llvm.org/ce/z/SHHW4d
Reviewed By: nikic
Differential Revision: https://reviews.llvm.org/D104741
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| .. | ||
| AliasSet | ||
| AssumptionCache | ||
| BasicAA | ||
| BlockFrequencyInfo | ||
| BranchProbabilityInfo | ||
| CallGraph | ||
| CFLAliasAnalysis | ||
| CostModel | ||
| DDG | ||
| Delinearization | ||
| DemandedBits | ||
| DependenceAnalysis | ||
| DivergenceAnalysis | ||
| DominanceFrontier | ||
| Dominators | ||
| FunctionPropertiesAnalysis | ||
| GlobalsModRef | ||
| IRSimilarityIdentifier | ||
| IVUsers | ||
| LazyCallGraph | ||
| LazyValueAnalysis | ||
| LegacyDivergenceAnalysis | ||
| Lint | ||
| LoopAccessAnalysis | ||
| LoopCacheAnalysis/PowerPC | ||
| LoopInfo | ||
| LoopNestAnalysis | ||
| MemoryDependenceAnalysis | ||
| MemorySSA | ||
| MustExecute | ||
| PhiValues | ||
| PostDominators | ||
| ProfileSummary | ||
| RegionInfo | ||
| ScalarEvolution | ||
| ScopedNoAliasAA | ||
| StackSafetyAnalysis | ||
| TypeBasedAliasAnalysis | ||
| ValueTracking | ||
| alias-analysis-uses.ll | ||