[VFDatabase] Scalar functions are vector functions with VF =1

Summary:
Return scalar function when VF==1. The new trivial mapping scalar --> scalar when VF==1 to prevent false positive for "isVectorizable" query.

Author: masoud.ataei (Masoud Ataei)

Reviewers: Whitney (Whitney Tsang), fhahn (Florian Hahn), pjeeva01 (Jeeva P.), fpetrogalli (Francesco Petrogalli), rengolin (Renato Golin)

Reviewed By: fpetrogalli (Francesco Petrogalli)

Subscribers: hiraditya (Aditya Kumar), llvm-commits, LLVM

Tag: LLVM

Differential Revision: https://reviews.llvm.org/D78054

llvm/include/llvm/Analysis/VectorUtils.h

@@ -96,6 +96,12 @@ struct VFShape {
     assert(hasValidParameterList() && "Invalid parameter list");
   }
 
+  // Retrieve the VFShape that can be used to map a (scalar) function to itself,
+  // with VF = 1.
+  static VFShape getScalarShape(const CallInst &CI) {
+    return VFShape::get(CI, /*EC*/ {1, false}, /*HasGlobalPredicate*/ false);
+  }
+
   // Retrieve the basic vectorization shape of the function, where all
   // parameters are mapped to VFParamKind::Vector with \p EC
   // lanes. Specifies whether the function has a Global Predicate
@@ -186,6 +192,8 @@ void getVectorVariantNames(const CallInst &CI,
 class VFDatabase {
   /// The Module of the CallInst CI.
   const Module *M;
+  /// The CallInst instance being queried for scalar to vector mappings.
+  const CallInst &CI;
   /// List of vector functions descritors associated to the call
   /// instruction.
   const SmallVector<VFInfo, 8> ScalarToVectorMappings;
@@ -233,13 +241,16 @@ public:
 
   /// Constructor, requires a CallInst instance.
   VFDatabase(CallInst &CI)
-      : M(CI.getModule()), ScalarToVectorMappings(VFDatabase::getMappings(CI)) {
-  }
+      : M(CI.getModule()), CI(CI),
+        ScalarToVectorMappings(VFDatabase::getMappings(CI)) {}
   /// \defgroup VFDatabase query interface.
   ///
   /// @{
   /// Retrieve the Function with VFShape \p Shape.
   Function *getVectorizedFunction(const VFShape &Shape) const {
+    if (Shape == VFShape::getScalarShape(CI))
+      return CI.getCalledFunction();
+
     for (const auto &Info : ScalarToVectorMappings)
       if (Info.Shape == Shape)
         return M->getFunction(Info.VectorName);

llvm/lib/Transforms/Vectorize/LoopVectorize.cpp

@@ -4384,22 +4384,17 @@ void InnerLoopVectorizer::widenCallInstruction(CallInst &I, VPUser &ArgOperands,
       if (VF > 1)
         TysForDecl[0] = VectorType::get(CI->getType()->getScalarType(), VF);
       VectorF = Intrinsic::getDeclaration(M, ID, TysForDecl);
+      assert(VectorF && "Can't retrieve vector intrinsic.");
     } else {
       // Use vector version of the function call.
       const VFShape Shape =
           VFShape::get(*CI, {VF, false} /*EC*/, false /*HasGlobalPred*/);
 #ifndef NDEBUG
-        const SmallVector<VFInfo, 8> Infos = VFDatabase::getMappings(*CI);
-        assert(std::find_if(Infos.begin(), Infos.end(),
-                            [&Shape](const VFInfo &Info) {
-                              return Info.Shape == Shape;
-                            }) != Infos.end() &&
-               "Vector function shape is missing from the database.");
+      assert(VFDatabase(*CI).getVectorizedFunction(Shape) != nullptr &&
+             "Can't create vector function.");
 #endif
         VectorF = VFDatabase(*CI).getVectorizedFunction(Shape);
     }
-      assert(VectorF && "Can't create vector function.");
-
       SmallVector<OperandBundleDef, 1> OpBundles;
       CI->getOperandBundlesAsDefs(OpBundles);
       CallInst *V = Builder.CreateCall(VectorF, Args, OpBundles);

llvm/test/Transforms/LoopVectorize/vectorizeVFone.ll

@@ -0,0 +1,30 @@
+; RUN: opt < %s -passes=loop-vectorize -S 2>&1 | FileCheck %s
+
+target triple = "powerpc64le-unknown-linux-gnu"
+%type = type { [3 x double] }
+
+define void @getScalarFunc(double* %A, double* %C, %type* %B) #0 {
+; CHECK-LABEL: getScalarFunc
+; This check will catch also the massv version of the function.
+; CHECK-NOT: call fast <{{[0-9]+}} x double> @{{.*}}atan{{.*}}(<{{[0-9]+}} x double> %{{[0-9]+}})
+entry:
+  br label %for.body
+
+for.body: 
+  %i = phi i64 [ %inc, %for.body ], [ 0, %entry ]
+  %dummyload2 = load double, double* %A, align 8
+  %arrayidx.i24 = getelementptr inbounds %type, %type* %B, i64 %i, i32 0, i32 0
+  %_15 = load double, double* %arrayidx.i24, align 8
+  %call10 = tail call fast double @atan(double %_15) #1
+  %inc = add i64 %i, 1
+  %cmp = icmp ugt i64 1000, %inc
+  br i1 %cmp, label %for.body, label %for.end
+
+for.end: 
+  ret void
+}
+
+declare double @atan(double) local_unnamed_addr
+declare <2 x double> @__atand2_massv(<2 x double>) #1
+attributes #0 = { "target-cpu"="pwr9" }
+attributes #1 = { nounwind readnone "vector-function-abi-variant"="_ZGV_LLVM_N2v_atan(__atand2_massv)" }

llvm/unittests/Analysis/VectorUtilsTest.cpp

@@ -536,6 +536,24 @@ TEST_F(VFShapeAPITest, API_buildVFShape) {
   EXPECT_EQ(Shape, Expected);
 }
 
+TEST_F(VFShapeAPITest, API_getScalarShape) {
+  buildShape(/*VF*/ 1, /*IsScalable*/ false, /*HasGlobalPred*/ false);
+  EXPECT_EQ(VFShape::getScalarShape(*CI), Shape);
+}
+
+TEST_F(VFShapeAPITest, API_getVectorizedFunction) {
+  VFShape ScalarShape = VFShape::getScalarShape(*CI);
+  EXPECT_EQ(VFDatabase(*CI).getVectorizedFunction(ScalarShape),
+            M->getFunction("g"));
+
+  buildShape(/*VF*/ 1, /*IsScalable*/ true, /*HasGlobalPred*/ false);
+  EXPECT_EQ(VFDatabase(*CI).getVectorizedFunction(Shape), nullptr);
+  buildShape(/*VF*/ 1, /*IsScalable*/ false, /*HasGlobalPred*/ true);
+  EXPECT_EQ(VFDatabase(*CI).getVectorizedFunction(Shape), nullptr);
+  buildShape(/*VF*/ 1, /*IsScalable*/ true, /*HasGlobalPred*/ true);
+  EXPECT_EQ(VFDatabase(*CI).getVectorizedFunction(Shape), nullptr);
+}
+
 TEST_F(VFShapeAPITest, API_updateVFShape) {
 
   buildShape(/*VF*/ 2, /*IsScalable*/ false, /*HasGlobalPred*/ false);