diff options
Diffstat (limited to 'llvm/lib/Transforms/Vectorize/LoopVectorizationLegality.cpp')
| -rw-r--r-- | llvm/lib/Transforms/Vectorize/LoopVectorizationLegality.cpp | 24 |
1 files changed, 22 insertions, 2 deletions
diff --git a/llvm/lib/Transforms/Vectorize/LoopVectorizationLegality.cpp b/llvm/lib/Transforms/Vectorize/LoopVectorizationLegality.cpp index 49f8658ef45..f23347e9cf6 100644 --- a/llvm/lib/Transforms/Vectorize/LoopVectorizationLegality.cpp +++ b/llvm/lib/Transforms/Vectorize/LoopVectorizationLegality.cpp @@ -436,8 +436,6 @@ static bool hasOutsideLoopUser(const Loop *TheLoop, Instruction *Inst, SmallPtrSetImpl<Value *> &AllowedExit) { // Reductions, Inductions and non-header phis are allowed to have exit users. All // other instructions must not have external users. - // TODO: Non-phi instructions can also be taught to have exit users, now that - // we know how to extract the last scalar element from the loop. if (!AllowedExit.count(Inst)) // Check that all of the users of the loop are inside the BB. for (User *U : Inst->users()) { @@ -626,6 +624,20 @@ bool LoopVectorizationLegality::canVectorizeInstrs() { continue; } + // TODO: Instead of recording the AllowedExit, it would be good to record the + // complementary set: NotAllowedExit. These include (but may not be + // limited to): + // 1. Reduction phis as they represent the one-before-last value, which + // is not available when vectorized + // 2. Induction phis and increment when SCEV predicates cannot be used + // outside the loop - see addInductionPhi + // 3. Non-Phis with outside uses when SCEV predicates cannot be used + // outside the loop - see call to hasOutsideLoopUser in the non-phi + // handling below + // 4. FirstOrderRecurrence phis that can possibly be handled by + // extraction. + // By recording these, we can then reason about ways to vectorize each + // of these NotAllowedExit. InductionDescriptor ID; if (InductionDescriptor::isInductionPHI(Phi, TheLoop, PSE, ID)) { addInductionPhi(Phi, ID, AllowedExit); @@ -718,6 +730,14 @@ bool LoopVectorizationLegality::canVectorizeInstrs() { // Reduction instructions are allowed to have exit users. // All other instructions must not have external users. if (hasOutsideLoopUser(TheLoop, &I, AllowedExit)) { + // We can safely vectorize loops where instructions within the loop are + // used outside the loop only if the SCEV predicates within the loop is + // same as outside the loop. Allowing the exit means reusing the SCEV + // outside the loop. + if (PSE.getUnionPredicate().isAlwaysTrue()) { + AllowedExit.insert(&I); + continue; + } ORE->emit(createMissedAnalysis("ValueUsedOutsideLoop", &I) << "value cannot be used outside the loop"); return false; |
