[InterleavedAccessPass] Don't increase the number of bytes loaded.

Even if the interleaving transform would otherwise be legal, we shouldn't
introduce an interleaved load that is wider than the original load: it might
have undefined behavior.

It might be possible to perform some sort of mask-narrowing transform in
some cases (using a narrower interleaved load, then extending the
results using shufflevectors).  But I haven't tried to implement that,
at least for now.

Fixes https://bugs.llvm.org/show_bug.cgi?id=41245 .

Differential Revision: https://reviews.llvm.org/D59954

llvm-svn: 357212

1 files changed, 9 insertions, 3 deletions

diff --git a/llvm/lib/CodeGen/InterleavedAccessPass.cpp b/llvm/lib/CodeGen/InterleavedAccessPass.cpp
index 2f8012aeeef..14bc560a561 100644
--- a/llvm/lib/CodeGen/InterleavedAccessPass.cpp
+++ b/llvm/lib/CodeGen/InterleavedAccessPass.cpp
@@ -163,14 +163,19 @@ static bool isDeInterleaveMaskOfFactor(ArrayRef<int> Mask, unsigned Factor,
 ///     <0, 2, 4, 6>    (mask of index 0 to extract even elements)
 ///     <1, 3, 5, 7>    (mask of index 1 to extract odd elements)
 static bool isDeInterleaveMask(ArrayRef<int> Mask, unsigned &Factor,
-                               unsigned &Index, unsigned MaxFactor) {
+                               unsigned &Index, unsigned MaxFactor,
+                               unsigned NumLoadElements) {
   if (Mask.size() < 2)
     return false;
 
   // Check potential Factors.
-  for (Factor = 2; Factor <= MaxFactor; Factor++)
+  for (Factor = 2; Factor <= MaxFactor; Factor++) {
+    // Make sure we don't produce a load wider than the input load.
+    if (Mask.size() * Factor > NumLoadElements)
+      return false;
     if (isDeInterleaveMaskOfFactor(Mask, Factor, Index))
       return true;
+  }
 
   return false;
 }
@@ -302,9 +307,10 @@ bool InterleavedAccess::lowerInterleavedLoad(
 
   unsigned Factor, Index;
 
+  unsigned NumLoadElements = LI->getType()->getVectorNumElements();
   // Check if the first shufflevector is DE-interleave shuffle.
   if (!isDeInterleaveMask(Shuffles[0]->getShuffleMask(), Factor, Index,
-                          MaxFactor))
+                          MaxFactor, NumLoadElements))
     return false;
 
   // Holds the corresponding index for each DE-interleave shuffle.