[VectorUtils] Introduce the Vector Function Database (VFDatabase).

This patch introduced the VFDatabase, the framework proposed in
http://lists.llvm.org/pipermail/llvm-dev/2019-June/133484.html. [*]

In this patch the VFDatabase is used to bridge the TargetLibraryInfo
(TLI) calls that were previously used to query for the availability of
vector counterparts of scalar functions.

The VFISAKind field `ISA` of VFShape have been moved into into VFInfo,
under the assumption that different vector ISAs may provide the same
vector signature. At the moment, the vectorizer accepts any of the
available ISAs as long as the signature provided by the VFDatabase
matches the one expected in the vectorization process. For example,
when targeting AVX or AVX2, which both have 256-bit registers, the IR
signature of the two vector functions associated to the two ISAs is
the same. The `getVectorizedFunction` method at the moment returns the
first available match. We will need to add more heuristics to the
search system to decide which of the available version (TLI, AVX,
AVX2, ...)  the system should prefer, when multiple versions with the
same VFShape are present.

Some of the code in this patch is based on the work done by Sumedh
Arani in https://reviews.llvm.org/D66025.

[*] Notice that in the proposal the VFDatabase was called SVFS. The
name VFDatabase is more in line with LLVM recommendations for
naming classes and variables.

Differential Revision: https://reviews.llvm.org/D67572

1 files changed, 6 insertions, 2 deletions

diff --git a/llvm/lib/Analysis/LazyCallGraph.cpp b/llvm/lib/Analysis/LazyCallGraph.cpp
index ef31c1e0ba8..a9dd5e01280 100644
--- a/llvm/lib/Analysis/LazyCallGraph.cpp
+++ b/llvm/lib/Analysis/LazyCallGraph.cpp
@@ -15,6 +15,7 @@
 #include "llvm/ADT/SmallVector.h"
 #include "llvm/ADT/iterator_range.h"
 #include "llvm/Analysis/TargetLibraryInfo.h"
+#include "llvm/Analysis/VectorUtils.h"
 #include "llvm/Config/llvm-config.h"
 #include "llvm/IR/CallSite.h"
 #include "llvm/IR/Function.h"
@@ -146,8 +147,11 @@ LLVM_DUMP_METHOD void LazyCallGraph::Node::dump() const {
 static bool isKnownLibFunction(Function &F, TargetLibraryInfo &TLI) {
   LibFunc LF;
 
-  // Either this is a normal library function or a "vectorizable" function.
-  return TLI.getLibFunc(F, LF) || TLI.isFunctionVectorizable(F.getName());
+  // Either this is a normal library function or a "vectorizable"
+  // function.  Not using the VFDatabase here because this query
+  // is related only to libraries handled via the TLI.
+  return TLI.getLibFunc(F, LF) ||
+         TLI.isKnownVectorFunctionInLibrary(F.getName());
 }
 
 LazyCallGraph::LazyCallGraph(