iverilog/devel/sv_call_chain.md

SystemVerilog chained calls: a().b()

This note describes the parser and elaboration support for chained calls: a function call whose value is a class handle, followed by one or more .method(args) segments (e.g. get_c().f(), a().b().c()).

Language shape

• Parse: A dedicated nonterminal call_chain_expr in parse.y builds a left-associated chain:
  • hierarchy_identifier attribute_list_opt argument_list_parens — first call;
  • call_chain_expr '.' hierarchy_identifier attribute_list_opt argument_list_parens — each further segment.
• expr_primary includes call_chain_expr before the bare hierarchy_identifier alternative so id ( is parsed as a call, not as an identifier plus a stray (.

Parse tree (PExpr)

• PECallFunction (PExpr.h / PExpr.cc):
  • Optional chain_prefix_: inner PExpr for the prefix (another PECallFunction for longer chains).
  • Constructors and accessors: peek_path(), peek_chain_prefix().
• pform_make_chained_call_function (pform.cc) — requires SystemVerilog; builds PECallFunction(prefix, method_name, args).

Elaboration (elab_expr.cc)

• PECallFunction::elaborate_expr_ delegates to elaborate_expr_chain_ when chain_prefix_ is set.
• elaborate_class_method_net_this_ passes the elaborated prefix as the implicit this argument (first parameter slot), including nested NetEUFunc for inner calls — not only NetESignal(net).
• resolve_call_chain_prefix_class (static helper) resolves the class type of the prefix for multi-hop chains (e.g. width checks), walking the chain prefix recursively instead of searching only the tail name.

Dump / debug

• pform_dump.cc prints chained calls with a prefix. prefix before the method path.

Regression

• ivtest/ivltests/sv_call_chain_method1.v
• ivtest/vvp_tests/sv_call_chain_method1.json (-g2012)
• Listed in ivtest/regress-vvp.list as sv_call_chain_method1.

Using a locally built iverilog

iverilog invokes the installed compiler under your prefix, typically $PREFIX/lib/ivl/ivl, not the ivl binary in the build tree. After changing the parser, reinstall or copy the new ivl into that lib directory so iverilog picks up the change; otherwise chained-call syntax may still fail with a syntax error while a direct ./ivl -C... test from the build tree succeeds.

# Example after building in-tree
make install
# or copy only the compiler binary to your existing install
cp ivl "$PREFIX/lib/ivl/ivl"

Related files (non-exhaustive)

Area	Files
Grammar	parse.y (call_chain_expr, expr_primary)
Parse form	pform.cc, pform.h
AST	PExpr.h, PExpr.cc
Elab	elab_expr.cc
Dump	pform_dump.cc