[xlscc] Add hls_block pragma and attribute for multi-block designs

Beginning of ping-pong implementation.

PiperOrigin-RevId: 698540382

xls/contrib/xlscc/cc_parser.cc

@@ -202,6 +202,42 @@ struct XlsTopAttrInfo : public clang::ParsedAttrInfo {
 static clang::ParsedAttrInfoRegistry::Add<XlsTopAttrInfo> hls_top(
     "hls_top", "Marks a function as the top function of an HLS block.");
 
+struct XlsBlockAttrInfo : public clang::ParsedAttrInfo {
+  XlsBlockAttrInfo() {
+    // GNU-style __attribute__(("hls_block")) and C++/C23-style [[hls_block]]
+    // and [[xlscc::hls_block]] supported.
+    static constexpr Spelling S[] = {
+        {clang::ParsedAttr::AS_GNU, "hls_block"},
+        {clang::ParsedAttr::AS_C23, "hls_block"},
+        {clang::ParsedAttr::AS_CXX11, "hls_block"},
+        {clang::ParsedAttr::AS_CXX11, "xlscc::hls_block"}};
+    Spellings = S;
+  }
+
+  bool diagAppertainsToDecl(clang::Sema& S, const clang::ParsedAttr& Attr,
+                            const clang::Decl* D) const override {
+    // This attribute appertains to functions only.
+    if (!isa<clang::FunctionDecl>(D)) {
+      S.Diag(Attr.getLoc(), clang::diag::warn_attribute_wrong_decl_type_str)
+          << Attr << Attr.isRegularKeywordAttribute() << "functions";
+      return false;
+    }
+    return true;
+  }
+
+  AttrHandling handleDeclAttribute(
+      clang::Sema& S, clang::Decl* D,
+      const clang::ParsedAttr& Attr) const override {
+    // Attach an annotate attribute to the Decl.
+    D->addAttr(clang::AnnotateAttr::Create(S.Context, "hls_block", nullptr, 0,
+                                           Attr.getRange()));
+    return AttributeApplied;
+  }
+};
+static clang::ParsedAttrInfoRegistry::Add<XlsBlockAttrInfo> hls_block(
+    "hls_block",
+    "Marks a function its own HLS block, below the top in the hierarchy.");
+
 struct XlsAllowDefaultPadAttrInfo : public clang::ParsedAttrInfo {
   XlsAllowDefaultPadAttrInfo() {
     // GNU-style __attribute__(("hls_array_allow_default_pad")) and
@@ -777,6 +813,24 @@ static clang::PragmaHandlerRegistry::Add<HlsTopPragmaHandler> hls_top_pragma(
     "hls_top",
     "Pragma to mark a function or method as the entrypoint for translation.");
 
+class HlsBlockPragmaHandler : public HlsArgsPragmaHandler {
+ public:
+  explicit HlsBlockPragmaHandler()
+      : HlsArgsPragmaHandler("hls_block", /*num_args=*/0) {}
+
+  void HandlePragma(clang::Preprocessor& PP, clang::PragmaIntroducer Introducer,
+                    clang::Token& firstToken,
+                    const std::vector<clang::Token>& toks) override {
+    GenerateAnnotation(PP, clang::PragmaHandler::getName(), firstToken,
+                       /*arguments=*/{});
+  }
+};
+
+static clang::PragmaHandlerRegistry::Add<HlsBlockPragmaHandler>
+    hls_block_pragma("hls_block",
+                     "Pragma to mark a function or method as the entrypoint "
+                     "for translation.");
+
 class HlsAllowDefaultPadPragmaHandler : public HlsArgsPragmaHandler {
  public:
   explicit HlsAllowDefaultPadPragmaHandler()

xls/contrib/xlscc/unit_tests/cc_parser_test.cc

@@ -25,6 +25,7 @@
 #include "absl/status/status_matchers.h"
 #include "absl/status/statusor.h"
 #include "clang/include/clang/AST/Attr.h"
+#include "clang/include/clang/AST/AttrIterator.h"
 #include "clang/include/clang/AST/Attrs.inc"
 #include "clang/include/clang/AST/Decl.h"
 #include "clang/include/clang/AST/Expr.h"
@@ -270,6 +271,33 @@ TEST_F(CCParserTest, TopNotFound) {
               absl_testing::StatusIs(absl::StatusCode::kNotFound));
 }
 
+TEST_F(CCParserTest, Block) {
+  xlscc::CCParser parser;
+
+  const std::string cpp_src = R"(
+    #pragma hls_block
+    int bar(int a, int b) {
+      const int foo = a + b;
+      return foo+1;
+    }
+  )";
+
+  XLS_ASSERT_OK(
+      ScanTempFileWithContent(cpp_src, {}, &parser, /*top_name=*/"bar"));
+  XLS_ASSERT_OK_AND_ASSIGN(const auto* top_ptr, parser.GetTopFunction());
+  ASSERT_NE(top_ptr, nullptr);
+  EXPECT_EQ(top_ptr->getNameAsString(), "bar");
+  top_ptr->specific_attrs<clang::AnnotateAttr>();
+
+  const clang::AttrVec& attrs = top_ptr->getAttrs();
+  ASSERT_EQ(attrs.size(), 1);
+  const clang::Attr* attr = attrs.data()[0];
+  const clang::AnnotateAttr* annotate =
+      llvm::dyn_cast<clang::AnnotateAttr>(attr);
+  ASSERT_NE(annotate, nullptr);
+  EXPECT_EQ(annotate->getAnnotation(), "hls_block");
+}
+
 TEST_F(CCParserTest, SourceMeta) {
   xlscc::CCParser parser;