Const-string args were pinned (AddRef before the call, Release after)
regardless of shape. ConstArgMode now classifies them: string literals
and named consts are immortal and emit no ARC ops at all; +1 owned
temps (function/method/getter returns) emit a single post-call Release
that consumes the transferred reference — previously these leaked one
buffer per call (the pin pair netted to zero and EmitOwnedArgReleases
deliberately skipped const-string params); every other shape keeps the
pin. The hot TStringList lookup signatures (Compare, KeyEquals,
HashOf, Find, FindSorted, IndexOf) become const.
Borrowed elision for plain local variables — the larger win — is
deliberately NOT enabled: it is sound at the ARC level, but removing
the balanced pin pairs changes caller register allocation and exposes a
latent use-before-def of a callee-saved register in the native
backend's EmitInterfaceCall (a second-generation compiler then reads
the caller's leftover %r13 as an AST pointer and crashes). The full
repro and bisect trail are recorded in the bug log; the camPin branch
carries a pointer to it.
Verified through two self-hosted generations plus both fixpoints;
contract pinned by 7 IR tests in cp.test.constarg.pas.
91f44ec823