[LV] Tail-folding, runtime scev checks

[SjoerdMeijer]

Summary

Now that we allow tail-folding, not only when we optimise for size, make
sure we do not run in this assert.

[Ayal]

llvm/lib/Transforms/Vectorize/LoopVectorize.cpp

2699 ↗

(On Diff #217805)

Error message should be updated as well.

llvm/test/Transforms/LoopVectorize/X86/tail-folding-scevcheck.ll

12 ↗

(On Diff #217805)

Better also check instructions, not only labels?

[SjoerdMeijer]

Thanks, comments addressed

[SjoerdMeijer]

friendly ping

llvm/trunk/lib/Transforms/Vectorize/LoopVectorize.cpp

SCEVExpander Exp(*PSE.getSE(), Bypass->getModule()->getDataLayout(),
                    "scev.check");
   Value *SCEVCheck =
       Exp.expandCodeForPredicate(&PSE.getUnionPredicate(), BB->getTerminator());
 
   if (auto *C = dyn_cast<ConstantInt>(SCEVCheck))
     if (C->isZero())
       return;
 
-  assert(!Cost->foldTailByMasking() &&
-         "Cannot SCEV check stride or overflow when folding tail");
+  assert(!BB->getParent()->hasOptSize() &&
+         "Cannot SCEV check stride or overflow when optimizing for size");
 
   // Create a new block containing the stride check.
   BB->setName("vector.scevcheck");
   auto *NewBB = BB->splitBasicBlock(BB->getTerminator(), "vector.ph");
   // Update dominator tree immediately if the generated block is a
   // LoopBypassBlock because SCEV expansions to generate loop bypass
   // checks may query it before the current function is finished.
   DT->addNewBlock(NewBB, BB);