[SLP] Enable 64-bit wide vectorization on AArch64

ARM Neon has native support for half-sized vector registers (64 bits).  This
is beneficial for example for 2D and 3D graphics.  This patch adds the option
to lower MinVecRegSize from 128 via a TTI in the SLP Vectorizer.

*** Performance Analysis

This change was motivated by some internal benchmarks but it is also
beneficial on SPEC and the LLVM testsuite.

The results are with -O3 and PGO.  A negative percentage is an improvement.
The testsuite was run with a sample size of 4.

** SPEC

* CFP2006/482.sphinx3  -3.34%

A pretty hot loop is SLP vectorized resulting in nice instruction reduction.
This used to be a +22% regression before rL299482.

* CFP2000/177.mesa     -3.34%
* CINT2000/256.bzip2   +6.97%

My current plan is to extend the fix in rL299482 to i16 which brings the
regression down to +2.5%.  There are also other problems with the codegen in
this loop so there is further room for improvement.

** LLVM testsuite

* SingleSource/Benchmarks/Misc/ReedSolomon               -10.75%

There are multiple small SLP vectorizations outside the hot code.  It's a bit
surprising that it adds up to 10%.  Some of this may be code-layout noise.

* MultiSource/Benchmarks/VersaBench/beamformer/beamformer -8.40%

The opt-viewer screenshot can be seen at F3218284.  We start at a colder store
but the tree leads us into the hottest loop.

* MultiSource/Applications/lambda-0.1.3/lambda            -2.68%
* MultiSource/Benchmarks/Bullet/bullet                    -2.18%

This is using 3D vectors.

* SingleSource/Benchmarks/Shootout-C++/Shootout-C++-lists +6.67%

Noise, binary is unchanged.

* MultiSource/Benchmarks/Ptrdist/anagram/anagram          +4.90%

There is an additional SLP in the cold code.  The test runs for ~1sec and
prints out over 2000 lines. This is most likely noise.

* MultiSource/Applications/aha/aha                        +1.63%
* MultiSource/Applications/JM/lencod/lencod               +1.41%
* SingleSource/Benchmarks/Misc/richards_benchmark         +1.15%

Differential Revision: https://reviews.llvm.org/D31965

llvm-svn: 303116

1 files changed, 8 insertions, 0 deletions

diff --git a/llvm/lib/Target/AArch64/AArch64Subtarget.cpp b/llvm/lib/Target/AArch64/AArch64Subtarget.cpp
index abdeac019a1..1c81d34014f 100644
--- a/llvm/lib/Target/AArch64/AArch64Subtarget.cpp
+++ b/llvm/lib/Target/AArch64/AArch64Subtarget.cpp
@@ -91,6 +91,8 @@ void AArch64Subtarget::initializeProperties() {
   case Falkor:
     MaxInterleaveFactor = 4;
     VectorInsertExtractBaseCost = 2;
+    // FIXME: remove this to enable 64-bit SLP if performance looks good.
+    MinVectorRegisterBitWidth = 128;
     break;
   case Kryo:
     MaxInterleaveFactor = 4;
@@ -99,6 +101,8 @@ void AArch64Subtarget::initializeProperties() {
     PrefetchDistance = 740;
     MinPrefetchStride = 1024;
     MaxPrefetchIterationsAhead = 11;
+    // FIXME: remove this to enable 64-bit SLP if performance looks good.
+    MinVectorRegisterBitWidth = 128;
     break;
   case ThunderX2T99:
     CacheLineSize = 64;
@@ -108,6 +112,8 @@ void AArch64Subtarget::initializeProperties() {
     PrefetchDistance = 128;
     MinPrefetchStride = 1024;
     MaxPrefetchIterationsAhead = 4;
+    // FIXME: remove this to enable 64-bit SLP if performance looks good.
+    MinVectorRegisterBitWidth = 128;
     break;
   case ThunderX:
   case ThunderXT88:
@@ -116,6 +122,8 @@ void AArch64Subtarget::initializeProperties() {
     CacheLineSize = 128;
     PrefFunctionAlignment = 3;
     PrefLoopAlignment = 2;
+    // FIXME: remove this to enable 64-bit SLP if performance looks good.
+    MinVectorRegisterBitWidth = 128;
     break;
   case CortexA35: break;
   case CortexA53: break;