[clang] [llvm] [Vectorize][OpenMP] Support header-provided declare simd math variants (PR #189523)

[Alexey Bataev via cfe-commits]

================
@@ -11919,29 +11211,196 @@ evaluateCDTSize(const FunctionDecl *FD,
   return C.getTypeSize(CDT);
 }
 
+/// Mangle the parameter part of the vector function name according to
+/// their OpenMP classification. The mangling function is defined in
+/// section 4.5 of the AAVFABI(2021Q1).
+static std::string mangleVectorParameters(ArrayRef<ParamAttrTy> ParamAttrs) {
+  SmallString<256> Buffer;
+  llvm::raw_svector_ostream Out(Buffer);
+  for (const auto &ParamAttr : ParamAttrs) {
+    switch (ParamAttr.Kind) {
+    case Linear:
+      Out << 'l';
+      break;
+    case LinearRef:
+      Out << 'R';
+      break;
+    case LinearUVal:
+      Out << 'U';
+      break;
+    case LinearVal:
+      Out << 'L';
+      break;
+    case Uniform:
+      Out << 'u';
+      break;
+    case Vector:
+      Out << 'v';
+      break;
+    }
+    if (ParamAttr.HasVarStride)
+      Out << "s" << ParamAttr.StrideOrArg;
+    else if (ParamAttr.Kind == Linear || ParamAttr.Kind == LinearRef ||
+             ParamAttr.Kind == LinearUVal || ParamAttr.Kind == LinearVal) {
+      // Don't print the step value if it is not present or if it is
+      // equal to 1.
+      if (ParamAttr.StrideOrArg < 0)
+        Out << 'n' << -ParamAttr.StrideOrArg;
+      else if (ParamAttr.StrideOrArg != 1)
+        Out << ParamAttr.StrideOrArg;
+    }
+
+    if (!!ParamAttr.Alignment)
+      Out << 'a' << ParamAttr.Alignment;
+  }
+
+  return std::string(Out.str());
+}
+
+static void
+emitX86DeclareSimdFunction(const FunctionDecl *FD, llvm::Function *Fn,
+                           const llvm::APSInt &VLENVal,
+                           ArrayRef<ParamAttrTy> ParamAttrs,
+                           OMPDeclareSimdDeclAttr::BranchStateTy State) {
+  struct ISADataTy {
+    char ISA;
+    unsigned VecRegSize;
+  };
+  ISADataTy ISAData[] = {
+      {
+          'b', 128
+      }, // SSE
+      {
+          'c', 256
+      }, // AVX
+      {
+          'd', 256
+      }, // AVX2
+      {
+          'e', 512
+      }, // AVX512
+  };
+  llvm::SmallVector<char, 2> Masked;
+  switch (State) {
+  case OMPDeclareSimdDeclAttr::BS_Undefined:
+    Masked.push_back('N');
+    Masked.push_back('M');
+    break;
+  case OMPDeclareSimdDeclAttr::BS_Notinbranch:
+    Masked.push_back('N');
+    break;
+  case OMPDeclareSimdDeclAttr::BS_Inbranch:
+    Masked.push_back('M');
+    break;
+  }
+  for (char Mask : Masked) {
+    for (const ISADataTy &Data : ISAData) {
+      SmallString<256> Buffer;
+      llvm::raw_svector_ostream Out(Buffer);
+      Out << "_ZGV" << Data.ISA << Mask;
+      if (!VLENVal) {
+        unsigned NumElts = evaluateCDTSize(FD, ParamAttrs);
+        assert(NumElts && "Non-zero simdlen/cdtsize expected");
+        Out << llvm::APSInt::getUnsigned(Data.VecRegSize / NumElts);
+      } else {
+        Out << VLENVal;
+      }
+      Out << mangleVectorParameters(ParamAttrs);
+      Out << '_' << Fn->getName();
+      Fn->addFnAttr(Out.str());
+    }
+  }
+}
+
+static void emitDeclareSimdVariantMetadata(CodeGenModule &CGM,
+                                           llvm::Function *Fn) {
+  llvm::SmallVector<std::string, 8> VariantMappings;
+  for (llvm::Attribute Attr : Fn->getAttributes().getFnAttrs()) {
+    if (!Attr.isStringAttribute())
+      continue;
+
+    StringRef VariantName = Attr.getKindAsString();
+    if (!VariantName.starts_with("_ZGV"))
+      continue;
+
+    std::optional<llvm::VFInfo> Info =
+        llvm::VFABI::tryDemangleForVFABI(VariantName, Fn->getFunctionType());
+    if (!Info)
+      continue;
+
+    llvm::FunctionType *VectorTy =
+        llvm::VFABI::createFunctionType(*Info, Fn->getFunctionType());
+    llvm::Function *VecFn = llvm::cast<llvm::Function>(
+        Fn->getParent()->getOrInsertFunction(Info->VectorName, VectorTy)
+            .getCallee());
+    CGM.addCompilerUsedGlobal(VecFn);
+    VariantMappings.push_back(std::string(VariantName));
+  }
+
+  if (VariantMappings.empty())
+    return;
+
+  SmallString<256> Buffer;
+  llvm::raw_svector_ostream Out(Buffer);
+  for (const std::string &VariantName : VariantMappings)
+    Out << VariantName << ',';
+  Buffer.pop_back();
+
+  Fn->removeFnAttr(llvm::VFABI::MappingsAttrName);
+  Fn->addFnAttr(llvm::VFABI::MappingsAttrName, Buffer.str());
+}
+
+static bool shouldEmitDeclareSimdVariantMetadata(const FunctionDecl *FD,
+                                                 const SourceManager &SM) {
+  if (!FD)
+    return false;
+
+  for (const FunctionDecl *Redecl : FD->redecls()) {
+    if (!Redecl->hasAttr<OMPDeclareSimdDeclAttr>())
+      continue;
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alexey-bataev wrote:

Same pattern as before, worth adding helper function

https://github.com/llvm/llvm-project/pull/189523