[LAA] Use type sizes when determining dependence.

In the isDependence function the code does not try hard enough
to determine the dependence between types. If the types are
different it simply gives up, whereas in fact what we really
care about are the type sizes. I've changed the code to compare
sizes instead of types.

Reviewed By: fhahn, sdesmalen

Differential Revision: https://reviews.llvm.org/D108763

1 files changed, 10 insertions, 11 deletions

diff --git a/llvm/lib/Analysis/LoopAccessAnalysis.cpp b/llvm/lib/Analysis/LoopAccessAnalysis.cpp
index 19a24ac..6444518 100644
--- a/llvm/lib/Analysis/LoopAccessAnalysis.cpp
+++ b/llvm/lib/Analysis/LoopAccessAnalysis.cpp
@@ -1568,11 +1568,12 @@ MemoryDepChecker::isDependent(const MemAccessInfo &A, unsigned AIdx,
 
   auto &DL = InnermostLoop->getHeader()->getModule()->getDataLayout();
   uint64_t TypeByteSize = DL.getTypeAllocSize(ATy);
+  bool HasSameSize =
+      DL.getTypeStoreSizeInBits(ATy) == DL.getTypeStoreSizeInBits(BTy);
   uint64_t Stride = std::abs(StrideAPtr);
   const SCEVConstant *C = dyn_cast<SCEVConstant>(Dist);
   if (!C) {
-    if (!isa<SCEVCouldNotCompute>(Dist) &&
-        TypeByteSize == DL.getTypeAllocSize(BTy) &&
+    if (!isa<SCEVCouldNotCompute>(Dist) && HasSameSize &&
         isSafeDependenceDistance(DL, *(PSE.getSE()),
                                  *(PSE.getBackedgeTakenCount()), *Dist, Stride,
                                  TypeByteSize))
@@ -1587,7 +1588,7 @@ MemoryDepChecker::isDependent(const MemAccessInfo &A, unsigned AIdx,
   int64_t Distance = Val.getSExtValue();
 
   // Attempt to prove strided accesses independent.
-  if (std::abs(Distance) > 0 && Stride > 1 && ATy == BTy &&
+  if (std::abs(Distance) > 0 && Stride > 1 && HasSameSize &&
       areStridedAccessesIndependent(std::abs(Distance), Stride, TypeByteSize)) {
     LLVM_DEBUG(dbgs() << "LAA: Strided accesses are independent\n");
     return Dependence::NoDep;
@@ -1598,7 +1599,7 @@ MemoryDepChecker::isDependent(const MemAccessInfo &A, unsigned AIdx,
     bool IsTrueDataDependence = (AIsWrite && !BIsWrite);
     if (IsTrueDataDependence && EnableForwardingConflictDetection &&
         (couldPreventStoreLoadForward(Val.abs().getZExtValue(), TypeByteSize) ||
-         ATy != BTy)) {
+         !HasSameSize)) {
       LLVM_DEBUG(dbgs() << "LAA: Forward but may prevent st->ld forwarding\n");
       return Dependence::ForwardButPreventsForwarding;
     }
@@ -1608,21 +1609,19 @@ MemoryDepChecker::isDependent(const MemAccessInfo &A, unsigned AIdx,
   }
 
   // Write to the same location with the same size.
-  // Could be improved to assert type sizes are the same (i32 == float, etc).
   if (Val == 0) {
-    if (ATy == BTy)
+    if (HasSameSize)
       return Dependence::Forward;
     LLVM_DEBUG(
-        dbgs() << "LAA: Zero dependence difference but different types\n");
+        dbgs() << "LAA: Zero dependence difference but different type sizes\n");
     return Dependence::Unknown;
   }
 
   assert(Val.isStrictlyPositive() && "Expect a positive value");
 
-  if (ATy != BTy) {
-    LLVM_DEBUG(
-        dbgs()
-        << "LAA: ReadWrite-Write positive dependency with different types\n");
+  if (!HasSameSize) {
+    LLVM_DEBUG(dbgs() << "LAA: ReadWrite-Write positive dependency with "
+                         "different type sizes\n");
     return Dependence::Unknown;
   }