[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, 3 insertions, 2 deletions

diff --git a/llvm/lib/Transforms/Vectorize/LoopVectorizationLegality.cpp b/llvm/lib/Transforms/Vectorize/LoopVectorizationLegality.cpp
index 3f943f4c068..0072a7db94e 100644
--- a/llvm/lib/Transforms/Vectorize/LoopVectorizationLegality.cpp
+++ b/llvm/lib/Transforms/Vectorize/LoopVectorizationLegality.cpp
@@ -670,7 +670,7 @@ bool LoopVectorizationLegality::canVectorizeInstrs() {
       if (CI && !getVectorIntrinsicIDForCall(CI, TLI) &&
           !isa<DbgInfoIntrinsic>(CI) &&
           !(CI->getCalledFunction() && TLI &&
-            TLI->isFunctionVectorizable(CI->getCalledFunction()->getName()))) {
+            !VFDatabase::getMappings(*CI).empty())) {
         // If the call is a recognized math libary call, it is likely that
         // we can vectorize it given loosened floating-point constraints.
         LibFunc Func;
@@ -685,7 +685,8 @@ bool LoopVectorizationLegality::canVectorizeInstrs() {
           // but it's hard to provide meaningful yet generic advice.
           // Also, should this be guarded by allowExtraAnalysis() and/or be part
           // of the returned info from isFunctionVectorizable()?
-          reportVectorizationFailure("Found a non-intrinsic callsite",
+          reportVectorizationFailure(
+              "Found a non-intrinsic callsite",
               "library call cannot be vectorized. "
               "Try compiling with -fno-math-errno, -ffast-math, "
               "or similar flags",