Handle tricky case of abs.interp.'ing a `repeat` loop.
Cat's Eye Technologies
8 years ago
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Abstract interpretation extends to `if` blocks. The two incoming contexts are
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merged, and any storage locations poisoned in either context are considered
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poisoned in the result context.
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(Same should apply for `repeat` and `with` and, really, many other cases
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which there just aren't enough test cases for yet.)
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poisoned in the result context. (A similar case applies to `repeat` and
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`with`, but these are different too as there is only one block and it is always
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executed at least once.)
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Declarations can have block scope. Such declarations may only be used within
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the block in which they are declared. `reserve`d storage inside a block is not,
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= A: UpdatedWith (Immediate 8)
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If a location is poisoned in either branch of an `if`, it is poisoned
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after the `if`.
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after the `if`. Note there are several tests for this.
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| reserve byte score
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| routine update_score
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= update_score ([])
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= X: UpdatedWith (Immediate 4)
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= NamedLocation Nothing "score": UpdatedWith X
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Poisoning a high byte or low byte of a word poisons the whole word.
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| reserve word score
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| reserve byte temp
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| routine update_score
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| {
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| ldx #4
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| stx <score
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| }
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| routine main {
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| jsr update_score
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| lda >score
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| sta temp
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| }
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? routine 'main' does not preserve 'NamedLocation Nothing "score"'
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Some more tests...
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| assign word position $fb
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| reserve byte value
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| }
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| }
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? routine 'main' does not preserve 'A'
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A storage location poisoned in a `repeat` continues to be poisoned
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after the `repeat`.
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| reserve byte value
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| routine blah {
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| lda #123
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| }
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| routine main {
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| lda #33
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| ldy #255
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| repeat bne {
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| jsr blah
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| dey
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| }
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| sta value
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| }
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? routine 'main' does not preserve 'A'
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Oh, here's a tricky one. The accumulator isn't poisoned on the first run
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through the `repeat`, but it **is** on the second run through. We handle
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this simply by abstractly interpreting the `repeat`'s block twice — the
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second time in the context of having already interpreted it once.
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| reserve byte value
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| routine blah {
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| lda #123
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| }
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| routine main {
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| lda #33
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| ldy #255
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| repeat bne {
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| sta value
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| jsr blah
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| dey
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| }
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| }
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? routine 'main' does not preserve 'A'
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Poisoning a high byte or low byte of a word poisons the whole word.
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| reserve word score
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| reserve byte temp
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| routine update_score
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| {
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| ldx #4
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| stx <score
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| }
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| routine main {
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| jsr update_score
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| lda >score
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| sta temp
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| }
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? routine 'main' does not preserve 'NamedLocation Nothing "score"'
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| reserve word score
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| reserve byte temp
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| routine update_score
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| {
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| ldx #4
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| stx >score
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| }
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| routine main {
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| jsr update_score
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| lda <score
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| sta temp
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| }
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? routine 'main' does not preserve 'NamedLocation Nothing "score"'
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in
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mergeAlternateRoutCtxs nm routCtx1 routCtx2
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checkInstr nm (REPEAT _ branch blk) progCtx routCtx =
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-- TODO: oooh, this one's gonna be fun too
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--checkBlock blk progCtx routCtx
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routCtx
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-- we analyze the block twice, to simulate it being
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-- repeated. (see tests for a test case on this.
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let
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routCtx' = checkBlock nm blk progCtx routCtx
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routCtx'' = checkBlock nm blk progCtx routCtx'
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in
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routCtx''
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-- TODO -- THESE ARE WEAK --
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checkInstr nm (WITH _ blk) progCtx routCtx =
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