[vbtcl]

A constant function called from a parameter initializer is evaluated once per instance of the enclosing module, even when every instance passes the same arguments. On the PULP astral SoC, hsiao_ecc_pkg::hsiao_matrix(DataWidth, ProtWidth) is called 108 times with 6 distinct argument sets. It accounts for 145 s of a 148 s elaboration. The value is needed for each instance's instance-cache key, so the evaluation can't be skipped.

This change memoizes top-level constant function calls on the Compilation. The key is the subroutine, the eval flags, the AST flags and the exact argument values: integers compare width, sign and X/Z bits, and reals compare bit patterns, so +0.0 and -0.0 are different keys. A result is recorded only when the evaluation:

• took at least 64 steps,
• added no diagnostics to the EvalContext, and
• did not depend on the call site. NamedValueExpression::checkConstant flags any non-package parameter checked against the outermost frame's lookup location.

Calls made from inside a package, calls with a queue target or lvalues on the stack, class methods, tasks and subroutines with output arguments are never memoized. On a hit, the original step count is added to the context. If the hit would cross maxConstexprSteps, the call is evaluated for real so that it fails exactly as it would have. The memo is mutex-guarded and holds at most 65,536 entries.

Measured with the boson native-elab driver setup, getAllDiagnostics, 1 thread:

design	before	after
astral (carfield top)	112.3 s	8.6 s
carfield	27.5 s	4.4 s

The rendered diagnostics are byte-identical on both designs.

New tests in ParameterTests.cpp cover values across instances and generate blocks, +0.0/-0.0 arguments, the step limit with memo hits, and call-site-dependent diagnostics (ConstEvalIdUsedInCEBeforeDecl). The full unittests pass: 22082 assertions in 2204 test cases, with #3 applied too.

Ships to boson as scripts/patches/slang/0010-memoize-top-level-constant-function-calls.patch (partcleda/boson#13187).

🤖 Generated with Claude Code

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[vbtcl]

Pushed 6b20f34: std::unique_lock<std::mutex> instead of CTAD (clang -Wctad-maybe-unsupported under -Werror, which upstream CI hit), plus a test that calls a memoized function with array, string, queue, associative-array and shortreal arguments. Unit tests: 22084 assertions in 2205 test cases, all pass (with #3). boson's 0010 differs from this branch only in that lock spelling: gcc builds both the same way.