[LV] Support invariant addresses in speculation logic
Implement a TODO from rL371452, and handle loop invariant addresses in predicated blocks. If we can prove that the load is safe to speculate into the header, then we can avoid using a masked.load in favour of a normal load.
This is mostly about vectorization robustness. In the common case, it's generally expected that LICM/LoadStorePromotion would have eliminated such loads entirely.
Differential Revision: https://reviews.llvm.org/D67372
llvm-svn: 371745
diff --git a/llvm/lib/Analysis/Loads.cpp b/llvm/lib/Analysis/Loads.cpp
index ea98ca9..f689a17 100644
--- a/llvm/lib/Analysis/Loads.cpp
+++ b/llvm/lib/Analysis/Loads.cpp
@@ -198,18 +198,31 @@
DominatorTree &DT) {
auto &DL = LI->getModule()->getDataLayout();
Value *Ptr = LI->getPointerOperand();
+
+ APInt EltSize(DL.getIndexTypeSizeInBits(Ptr->getType()),
+ DL.getTypeStoreSize(LI->getType()));
+ unsigned Align = LI->getAlignment();
+ if (Align == 0)
+ Align = DL.getABITypeAlignment(LI->getType());
+
+ Instruction *HeaderFirstNonPHI = L->getHeader()->getFirstNonPHI();
+
+ // If given a uniform (i.e. non-varying) address, see if we can prove the
+ // access is safe within the loop w/o needing predication.
+ if (L->isLoopInvariant(Ptr))
+ return isDereferenceableAndAlignedPointer(Ptr, Align, EltSize, DL,
+ HeaderFirstNonPHI, &DT);
+
+ // Otherwise, check to see if we have a repeating access pattern where we can
+ // prove that all accesses are well aligned and dereferenceable.
auto *AddRec = dyn_cast<SCEVAddRecExpr>(SE.getSCEV(Ptr));
if (!AddRec || AddRec->getLoop() != L || !AddRec->isAffine())
return false;
auto* Step = dyn_cast<SCEVConstant>(AddRec->getStepRecurrence(SE));
if (!Step)
return false;
- APInt StepC = Step->getAPInt();
- APInt EltSize(DL.getIndexTypeSizeInBits(Ptr->getType()),
- DL.getTypeStoreSize(LI->getType()));
// TODO: generalize to access patterns which have gaps
- // TODO: handle uniform addresses (if not already handled by LICM)
- if (StepC != EltSize)
+ if (Step->getAPInt() != EltSize)
return false;
// TODO: If the symbolic trip count has a small bound (max count), we might
@@ -226,11 +239,6 @@
assert(SE.isLoopInvariant(StartS, L) && "implied by addrec definition");
Value *Base = StartS->getValue();
- Instruction *HeaderFirstNonPHI = L->getHeader()->getFirstNonPHI();
-
- unsigned Align = LI->getAlignment();
- if (Align == 0)
- Align = DL.getABITypeAlignment(LI->getType());
// For the moment, restrict ourselves to the case where the access size is a
// multiple of the requested alignment and the base is aligned.
// TODO: generalize if a case found which warrants