[LAA] Introduce enum for vectorization safety status (NFC).

This patch adds a VectorizationSafetyStatus enum, which will be extended
in a follow up patch to distinguish between 'safe with runtime checks'
and 'known unsafe' dependences.

Reviewers: anemet, anna, Ayal, hsaito

Reviewed By: Ayal

Differential Revision: https://reviews.llvm.org/D54892

llvm-svn: 349556

1 files changed, 12 insertions, 6 deletions

diff --git a/llvm/lib/Analysis/LoopAccessAnalysis.cpp b/llvm/lib/Analysis/LoopAccessAnalysis.cpp
index bc01f04..245f318 100644
--- a/llvm/lib/Analysis/LoopAccessAnalysis.cpp
+++ b/llvm/lib/Analysis/LoopAccessAnalysis.cpp
@@ -1221,18 +1221,19 @@ bool llvm::isConsecutiveAccess(Value *A, Value *B, const DataLayout &DL,
   return X == PtrSCEVB;
 }
 
-bool MemoryDepChecker::Dependence::isSafeForVectorization(DepType Type) {
+MemoryDepChecker::VectorizationSafetyStatus
+MemoryDepChecker::Dependence::isSafeForVectorization(DepType Type) {
   switch (Type) {
   case NoDep:
   case Forward:
   case BackwardVectorizable:
-    return true;
+    return VectorizationSafetyStatus::Safe;
 
   case Unknown:
   case ForwardButPreventsForwarding:
   case Backward:
   case BackwardVectorizableButPreventsForwarding:
-    return false;
+    return VectorizationSafetyStatus::Unsafe;
   }
   llvm_unreachable("unexpected DepType!");
 }
@@ -1317,6 +1318,11 @@ bool MemoryDepChecker::couldPreventStoreLoadForward(uint64_t Distance,
   return false;
 }
 
+void MemoryDepChecker::mergeInStatus(VectorizationSafetyStatus S) {
+  if (Status < S)
+    Status = S;
+}
+
 /// Given a non-constant (unknown) dependence-distance \p Dist between two
 /// memory accesses, that have the same stride whose absolute value is given
 /// in \p Stride, and that have the same type size \p TypeByteSize,
@@ -1652,7 +1658,7 @@ bool MemoryDepChecker::areDepsSafe(DepCandidates &AccessSets,
 
             Dependence::DepType Type =
                 isDependent(*A.first, A.second, *B.first, B.second, Strides);
-            SafeForVectorization &= Dependence::isSafeForVectorization(Type);
+            mergeInStatus(Dependence::isSafeForVectorization(Type));
 
             // Gather dependences unless we accumulated MaxDependences
             // dependences.  In that case return as soon as we find the first
@@ -1669,7 +1675,7 @@ bool MemoryDepChecker::areDepsSafe(DepCandidates &AccessSets,
                            << "Too many dependences, stopped recording\n");
               }
             }
-            if (!RecordDependences && !SafeForVectorization)
+            if (!RecordDependences && !isSafeForVectorization())
               return false;
           }
         ++OI;
@@ -1679,7 +1685,7 @@ bool MemoryDepChecker::areDepsSafe(DepCandidates &AccessSets,
   }
 
   LLVM_DEBUG(dbgs() << "Total Dependences: " << Dependences.size() << "\n");
-  return SafeForVectorization;
+  return isSafeForVectorization();
 }
 
 SmallVector<Instruction *, 4>