SplitLint knew that CALL restores A, B and Data Pointers 0 to 2, so a
pointer set before a call is still set after it. That is true, and it made
the tool give advice that was correct today and unsafe to take.
Of the 178 redundant SETDs it found across the corpus, 122 were redundant
ONLY because of that restore - the shape is everywhere, because it is how a
helper is given its arguments:
SETD.0 SbfsBlock
SETD.2 SbfsFileStart
CALL sbfsSetWord
SETD.0 SbfsBlock <- flagged
Removing that last line is right until sbfsSetWord is reached with RCAL,
which restores nothing - and that is not hypothetical, it is what RCAL was
added to this machine for, measured at close to halving the assembler's
memory traffic. The failure would also be silent from the linter's side: it
forgets everything across an RCAL, so it would stop reporting while the
removals stayed removed.
So a claim now ends at any call, for pointers and for registers, the way a
claim about carry already did. 257 warnings become 127, and the redundant
SETDs 178 become 54 - which is exactly the number an independent count of
"no CALL in between" had arrived at separately.
The fixture gained a SETD and an INIA repeated across a CALL, which must
stay quiet, and the harness fails with the old behaviour put back. Two
mistakes worth recording: the new expectations first pointed at the LABEL
above the repeats rather than the repeats, which passes for free because
nothing ever warns about a label; and the block landed in the middle of
another check's comment, leaving that comment describing the code below it
instead of its own.
SplitLint reports valid assembly that has a shorter direct expression:
zero loads that could be RSTA or RSTB, Q moved through the stack where MVQA
would do, self-cancelling push and pop pairs, assignments overwritten
before use, unreachable fallthrough, one-byte pointer moves that could be
INCD or DECD, a branch to the label directly below it, a SETD reloading an
address the pointer already holds, and branches whose carry is known.
Its model is deliberately local and conservative: every label and every
directive forgets all known state, so a claim only ever lives inside a
straight-line region. It knows the calling convention - CALL forgets DP3
and keeps the rest, RCAL and SWI forget everything - and it shares
assembly.o with the assembler, so an added opcode cannot leave it holding a
private copy of the instruction table.
260 warnings across the corpus, of which three were wrong in the way that
matters: branchTest.asm and interruptFlagTest.asm exist to check that a
branch whose carry is known behaves correctly, so a diagnostic saying the
outcome is known is exactly right and exactly unwanted.
A line whose comment says "splitlint: <reason>" is now not reported on. THE
REASON IS REQUIRED and a bare marker is refused, because a suppression
nobody explained outlives whatever made it necessary. Suppressed warnings
are not counted, so --fatal-warnings does not fail on one, and the number
of them is printed at the end so the claim is visible rather than silent.
Tests/lint.sh checked a TOTAL: twenty three warnings expected, twenty three
found. That number stays right while the thing behind it goes wrong - a
rule that stopped firing while another fired twice would pass, and so would
a rule reporting at the wrong line. It now checks which warning came out
and at which line, that nothing else came out, and that the four lines
meant to stay quiet did. Confirmed by breaking one rule's message and
watching it name that rule: the old assertion passed the same sabotage,
because the warning still fired and the count never moved.
Written with the user while I was away; my part is the suppression
mechanism, the harness rewrite, and the three marks in the test programs.
Anachronaut