[LV] Considier non-consecutive but vectorizable accesses for VF selection

When computing the smallest and largest types for selecting the maximum
vectorization factor, we currently ignore loads and stores of pointer types if
the memory access is non-consecutive. We do this because such accesses must be
scalarized regardless of vectorization factor, and thus shouldn't be considered
when determining the factor. This patch makes this check less aggressive by
also considering non-consecutive accesses that may be vectorized, such as
interleaved accesses. Because we don't know at the time of the check if an
accesses will certainly be vectorized (this is a cost model decision given a
particular VF), we consider all accesses that can potentially be vectorized.

Differential Revision: https://reviews.llvm.org/D30305

llvm-svn: 296747

2 files changed, 43 insertions, 3 deletions

diff --git a/llvm/lib/Transforms/Vectorize/LoopVectorize.cpp b/llvm/lib/Transforms/Vectorize/LoopVectorize.cpp
index 36570b49bb0..763ce083837 100644
--- a/llvm/lib/Transforms/Vectorize/LoopVectorize.cpp
+++ b/llvm/lib/Transforms/Vectorize/LoopVectorize.cpp
@@ -6326,9 +6326,16 @@ LoopVectorizationCostModel::getSmallestAndWidestTypes() {
         T = ST->getValueOperand()->getType();
 
       // Ignore loaded pointer types and stored pointer types that are not
-      // consecutive. However, we do want to take consecutive stores/loads of
-      // pointer vectors into account.
-      if (T->isPointerTy() && !isConsecutiveLoadOrStore(&I))
+      // vectorizable.
+      //
+      // FIXME: The check here attempts to predict whether a load or store will
+      //        be vectorized. We only know this for certain after a VF has
+      //        been selected. Here, we assume that if an access can be
+      //        vectorized, it will be. We should also look at extending this
+      //        optimization to non-pointer types.
+      //
+      if (T->isPointerTy() && !isConsecutiveLoadOrStore(&I) &&
+          !Legal->isAccessInterleaved(&I) && !Legal->isLegalGatherOrScatter(&I))
         continue;
 
       MinWidth = std::min(MinWidth,
diff --git a/llvm/test/Transforms/LoopVectorize/AArch64/smallest-and-widest-types.ll b/llvm/test/Transforms/LoopVectorize/AArch64/smallest-and-widest-types.ll
new file mode 100644
index 00000000000..1ae7dadeffd
--- /dev/null
+++ b/llvm/test/Transforms/LoopVectorize/AArch64/smallest-and-widest-types.ll
@@ -0,0 +1,33 @@
+; REQUIRES: asserts
+; RUN: opt < %s -loop-vectorize -debug-only=loop-vectorize -disable-output 2>&1 | FileCheck %s
+
+target datalayout = "e-m:e-i8:8:32-i16:16:32-i64:64-i128:128-n32:64-S128"
+target triple = "aarch64--linux-gnu"
+
+; CHECK-LABEL: Checking a loop in "interleaved_access"
+; CHECK:         The Smallest and Widest types: 64 / 64 bits
+;
+define void @interleaved_access(i8** %A, i64 %N) {
+for.ph:
+  br label %for.body
+
+for.body:
+  %i = phi i64 [ %i.next.3, %for.body ], [ 0, %for.ph ]
+  %tmp0 = getelementptr inbounds i8*, i8** %A, i64 %i
+  store i8* null, i8** %tmp0, align 8
+  %i.next.0 = add nuw nsw i64 %i, 1
+  %tmp1 = getelementptr inbounds i8*, i8** %A, i64 %i.next.0
+  store i8* null, i8** %tmp1, align 8
+  %i.next.1 = add nsw i64 %i, 2
+  %tmp2 = getelementptr inbounds i8*, i8** %A, i64 %i.next.1
+  store i8* null, i8** %tmp2, align 8
+  %i.next.2 = add nsw i64 %i, 3
+  %tmp3 = getelementptr inbounds i8*, i8** %A, i64 %i.next.2
+  store i8* null, i8** %tmp3, align 8
+  %i.next.3 = add nsw i64 %i, 4
+  %cond = icmp slt i64 %i.next.3, %N
+  br i1 %cond, label %for.body, label %for.end
+
+for.end:
+  ret void
+}