diff options
Diffstat (limited to 'lib/Analysis/ScalarEvolutionExpander.cpp')
-rw-r--r-- | lib/Analysis/ScalarEvolutionExpander.cpp | 41 |
1 files changed, 41 insertions, 0 deletions
diff --git a/lib/Analysis/ScalarEvolutionExpander.cpp b/lib/Analysis/ScalarEvolutionExpander.cpp index e7fe672ad3..b77f8d6ddc 100644 --- a/lib/Analysis/ScalarEvolutionExpander.cpp +++ b/lib/Analysis/ScalarEvolutionExpander.cpp @@ -1700,3 +1700,44 @@ unsigned SCEVExpander::replaceCongruentIVs(Loop *L, const DominatorTree *DT, } return NumElim; } + +namespace { +// Search for a SCEV subexpression that is not safe to expand. Any expression +// that may expand to a !isSafeToSpeculativelyExecute value is unsafe, namely +// UDiv expressions. We don't know if the UDiv is derived from an IR divide +// instruction, but the important thing is that we prove the denominator is +// nonzero before expansion. +// +// IVUsers already checks that IV-derived expressions are safe. So this check is +// only needed when the expression includes some subexpression that is not IV +// derived. +// +// Currently, we only allow division by a nonzero constant here. If this is +// inadequate, we could easily allow division by SCEVUnknown by using +// ValueTracking to check isKnownNonZero(). +struct SCEVFindUnsafe { + bool IsUnsafe; + + SCEVFindUnsafe(): IsUnsafe(false) {} + + bool follow(const SCEV *S) { + const SCEVUDivExpr *D = dyn_cast<SCEVUDivExpr>(S); + if (!D) + return true; + const SCEVConstant *SC = dyn_cast<SCEVConstant>(D->getRHS()); + if (SC && !SC->getValue()->isZero()) + return true; + IsUnsafe = true; + return false; + } + bool isDone() const { return IsUnsafe; } +}; +} + +namespace llvm { +bool isSafeToExpand(const SCEV *S) { + SCEVFindUnsafe Search; + visitAll(S, Search); + return !Search.IsUnsafe; +} +} |