Mark constants early to enable SCCP

[Qchan233]

When debugging, I found that the sccp optimization doesn't work using the following example, though constant folding does the work. I think it would be good that gets optimized early in sccp.

int test()
{
    int c;
    if (1) {
        c = 1;
    } else {
        c = 0;
    }

    return c;
}

---

Summary by cubic

Mark destinations of OP_load_constant as const in SCCP. This enables early constant propagation so SCCP optimizes trivial branches and assignments (e.g., returning a constant after an if/else).

• Bug Fixes
  • In simple_sccp, set rd->is_const when opcode == OP_load_constant to allow SCCP to recognize and propagate constants.

^{Written for commit 483a46a. Summary will update automatically on new commits.}

[jserv]

Make it slightly shorter. That is,

            if (insn->opcode == OP_load_constant)
                insn->rd->is_const = true;

[cubic-dev-ai]

No issues found across 1 file