Constrain PowerPC autovectorization to fix bug 15041.

Certain vector operations don't vectorize well with the current
PowerPC implementation.  Element insert/extract performs poorly
without VSX support because Altivec requires going through memory.
SREM, UREM, and VSELECT all produce bad scalar code.

There's a lot of work to do for the cost model before
autovectorization will be tuned well, and this is not an attempt to
address the larger problem.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@174660 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 19 insertions, 0 deletions

diff --git a/lib/Target/PowerPC/PPCTargetTransformInfo.cpp b/lib/Target/PowerPC/PPCTargetTransformInfo.cpp
index 88b63e65d1..f57d7643e1 100644
--- a/lib/Target/PowerPC/PPCTargetTransformInfo.cpp
+++ b/lib/Target/PowerPC/PPCTargetTransformInfo.cpp
@@ -194,6 +194,25 @@ unsigned PPCTTI::getVectorInstrCost(unsigned Opcode, Type *Val,
                                     unsigned Index) const {
   assert(Val->isVectorTy() && "This must be a vector type");
 
+  const unsigned Awful = 1000;
+
+  // Vector element insert/extract with Altivec is very expensive.
+  // Until VSX is available, avoid vectorizing loops that require
+  // these operations.
+  if (Opcode == ISD::EXTRACT_VECTOR_ELT ||
+      Opcode == ISD::INSERT_VECTOR_ELT)
+    return Awful;
+
+  // We don't vectorize SREM/UREM so well.  Constrain the vectorizer
+  // for those as well.
+  if (Opcode == ISD::SREM || Opcode == ISD::UREM)
+    return Awful;
+
+  // VSELECT is not yet implemented, leading to use of insert/extract
+  // and ISEL, hence not a good idea.
+  if (Opcode == ISD::VSELECT)
+    return Awful;
+
   return TargetTransformInfo::getVectorInstrCost(Opcode, Val, Index);
 }