[LoopDataPrefetch/Aarch64] Allow selective prefetching of large-strided accesses

Summary:
And use this TTI for Cyclone.  As it was explained in the original RFC
(http://thread.gmane.org/gmane.comp.compilers.llvm.devel/92758), the HW
prefetcher work up to 2KB strides.

I am also adding tests for this and the previous change (D17943):

* Cyclone prefetching accesses with a large stride
* Cyclone not prefetching accesses with a small stride
* Generic Aarch64 subtarget not prefetching either

Reviewers: hfinkel

Subscribers: aemerson, rengolin, llvm-commits, mzolotukhin

Differential Revision: http://reviews.llvm.org/D17945

llvm-svn: 263771

2 files changed, 14 insertions, 0 deletions

diff --git a/llvm/lib/Target/AArch64/AArch64TargetTransformInfo.cpp b/llvm/lib/Target/AArch64/AArch64TargetTransformInfo.cpp
index 5803e07dbcf..aee298998f3 100644
--- a/llvm/lib/Target/AArch64/AArch64TargetTransformInfo.cpp
+++ b/llvm/lib/Target/AArch64/AArch64TargetTransformInfo.cpp
@@ -25,6 +25,12 @@ static cl::opt<unsigned> CyclonePrefetchDistance(
     cl::desc("Number of instructions to prefetch ahead for Cyclone"),
     cl::init(280), cl::Hidden);
 
+// The HW prefetcher handles accesses with strides up to 2KB.
+static cl::opt<unsigned> CycloneMinPrefetchStride(
+    "cyclone-min-prefetch-stride",
+    cl::desc("Min stride to add prefetches for Cyclone"),
+    cl::init(2048), cl::Hidden);
+
 /// \brief Calculate the cost of materializing a 64-bit value. This helper
 /// method might only calculate a fraction of a larger immediate. Therefore it
 /// is valid to return a cost of ZERO.
@@ -590,3 +596,9 @@ unsigned AArch64TTIImpl::getPrefetchDistance() {
     return CyclonePrefetchDistance;
   return BaseT::getPrefetchDistance();
 }
+
+unsigned AArch64TTIImpl::getMinPrefetchStride() {
+  if (ST->isCyclone())
+    return CycloneMinPrefetchStride;
+  return BaseT::getMinPrefetchStride();
+}
diff --git a/llvm/lib/Target/AArch64/AArch64TargetTransformInfo.h b/llvm/lib/Target/AArch64/AArch64TargetTransformInfo.h
index ad711f511e5..a54db00e7d3 100644
--- a/llvm/lib/Target/AArch64/AArch64TargetTransformInfo.h
+++ b/llvm/lib/Target/AArch64/AArch64TargetTransformInfo.h
@@ -131,6 +131,8 @@ public:
   unsigned getCacheLineSize();
 
   unsigned getPrefetchDistance();
+
+  unsigned getMinPrefetchStride();
   /// @}
 };