[vast] Represent single-bit signed bitvectors as scalars.

Previously, they would be `wire signed [0:0]`. PiperOrigin-RevId: 682511756
hzeller · Oct 5, 2024 · a933ce3 · a933ce3
1 parent d8a8ca0
commit a933ce3
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Showing 3 changed files with 17 additions and 5 deletions.
diff --git a/xls/codegen/vast/vast.cc b/xls/codegen/vast/vast.cc
@@ -302,7 +302,12 @@ std::string ToString(Direction direction) {
 
 std::string ScalarType::Emit(LineInfo* line_info) const {
   // The `DataKind` preceding the type is enough.
-  return EmitNothing(this, line_info);
+  if (!is_signed_) {
+    return EmitNothing(this, line_info);
+  }
+  LineInfoStart(line_info, this);
+  LineInfoEnd(line_info, this);
+  return " signed";
 }
 
 std::string IntegerType::Emit(LineInfo* line_info) const {
@@ -345,8 +350,8 @@ BitVectorType* VerilogFile::BitVectorTypeNoScalar(int64_t bit_count,
 DataType* VerilogFile::BitVectorType(int64_t bit_count, const SourceInfo& loc,
                                      bool is_signed) {
   CHECK_GT(bit_count, 0);
-  if (bit_count == 1 && !is_signed) {
-    return ScalarType(loc);
+  if (bit_count == 1) {
+    return Make<verilog::ScalarType>(loc, is_signed);
   }
   return BitVectorTypeNoScalar(bit_count, loc, is_signed);
 }

diff --git a/xls/codegen/vast/vast.h b/xls/codegen/vast/vast.h
@@ -242,13 +242,20 @@ class DataType : public VastNode {
 //   wire foo;
 class ScalarType final : public DataType {
  public:
-  ScalarType(VerilogFile* file, const SourceInfo& loc) : DataType(file, loc) {}
+  ScalarType(VerilogFile* file, const SourceInfo& loc)
+      : DataType(file, loc), is_signed_(false) {}
+  ScalarType(bool is_signed, VerilogFile* file, const SourceInfo& loc)
+      : DataType(file, loc), is_signed_(is_signed) {}
 
   bool IsScalar() const final { return true; }
+  bool is_signed() const final { return is_signed_; }
   absl::StatusOr<int64_t> WidthAsInt64() const final { return 1; }
   absl::StatusOr<int64_t> FlatBitCountAsInt64() const final { return 1; }
   std::optional<Expression*> width() const final { return std::nullopt; }
   std::string Emit(LineInfo* line_info) const final;
+
+ private:
+  bool is_signed_;
 };
 
 // Represents an integer type. Example:

diff --git a/xls/codegen/vast/vast_test.cc b/xls/codegen/vast/vast_test.cc
@@ -88,7 +88,7 @@ TEST_P(VastTest, DataTypes) {
 
   DataType* s1 = f.BitVectorType(1, SourceInfo(), /*is_signed=*/true);
   EXPECT_FALSE(s1->IsUserDefined());
-  EXPECT_EQ(s1->EmitWithIdentifier(nullptr, "foo"), " signed [0:0] foo");
+  EXPECT_EQ(s1->EmitWithIdentifier(nullptr, "foo"), " signed foo");
   EXPECT_THAT(s1->WidthAsInt64(), IsOkAndHolds(1));
   EXPECT_THAT(s1->FlatBitCountAsInt64(), IsOkAndHolds(1));
   EXPECT_TRUE(s1->is_signed());