ImportVerilog: fix signedness propagation in ConversionExpression lowering

lib/Conversion/ImportVerilog/Expressions.cpp

@@ -969,7 +969,7 @@ struct RvalueExprVisitor : public ExprVisitor {
     auto type = context.convertType(*expr.type);
     if (!type)
       return {};
-    return context.convertRvalueExpression(expr.operand(), type);
+    return context.convertRvalueExpression(expr.operand(), type, expr.type->isSigned());
   }
 
   // Handle blocking and non-blocking assignments.
@@ -2517,6 +2517,15 @@ Value Context::convertRvalueExpression(const slang::ast::Expression &expr,
         materializeConversion(requiredType, value, expr.type->isSigned(), loc);
   return value;
 }
+Value Context::convertRvalueExpression(const slang::ast::Expression &expr,
+                                       Type requiredType,bool conversionIsSigned) {
+  auto loc = convertLocation(expr.sourceRange);
+  auto value = expr.visit(RvalueExprVisitor(*this, loc));
+  if (value && requiredType)
+    value =
+        materializeConversion(requiredType, value, conversionIsSigned, loc);
+  return value;
+}
 
 Value Context::convertLvalueExpression(const slang::ast::Expression &expr) {
   auto loc = convertLocation(expr.sourceRange);

lib/Conversion/ImportVerilog/ImportVerilogInternals.h

@@ -243,6 +243,10 @@ struct Context {
   // Convert an expression AST node to MLIR ops.
   Value convertRvalueExpression(const slang::ast::Expression &expr,
                                 Type requiredType = {});
+  // When materializing a conversion, the caller may need to override the
+  // source expression's signedness with the conversion's own semantics.
+  Value convertRvalueExpression(const slang::ast::Expression &expr,
+                                       Type requiredType,bool conversionIsSigned); 
   Value convertLvalueExpression(const slang::ast::Expression &expr);
 
   // Convert an assertion expression AST node to MLIR ops.

test/Conversion/ImportVerilog/conversion-signedness.sv

@@ -0,0 +1,24 @@
+// RUN: circt-verilog --ir-moore %s | FileCheck %s --check-prefix=MOORE
+// REQUIRES: slang
+
+module M(
+    input  logic [7:0]        in1,
+    input  logic signed [7:0] in2,
+    output logic signed [8:0] mux_out
+);
+  logic [7:0] unsigned_src;
+  logic signed [7:0] signed_src;
+
+  always_comb signed_src = in2 >>> 1;
+  always_comb unsigned_src = in1 >> 1;
+  always_comb mux_out = signed_src + unsigned_src;
+endmodule
+
+// MOORE-LABEL: moore.module @M(
+// MOORE: moore.procedure always_comb {
+// MOORE:   %[[SIGNED_READ:.+]] = moore.read %signed_src : <l8>
+// MOORE:   %[[SIGNED_ZEXT:.+]] = moore.zext %[[SIGNED_READ]] : l8 -> l9
+// MOORE-NOT: moore.sext
+// MOORE:   %[[UNSIGNED_READ:.+]] = moore.read %unsigned_src : <l8>
+// MOORE:   %[[UNSIGNED_ZEXT:.+]] = moore.zext %[[UNSIGNED_READ]] : l8 -> l9
+// MOORE:   %[[ADD:.+]] = moore.add %[[SIGNED_ZEXT]], %[[UNSIGNED_ZEXT]] : l9