Summary:
This allows further normalisation now that terms contain linear
expressions in normal form.
Reviewed By: skcho
Differential Revision: D23241499
fbshipit-source-id: f8e4e759c
Summary:
Linear arithmetic is able to simplify more atoms, eg `x+y <= x+y`
becomes `True` by normalising to "lhs - rhs <= 0". This does the first
step of normalisation, but to get True in this example we also need to
substitute inside atoms according to the linear equalities, which is the
next diff (for now we only substitute variables inside atoms for other
variables or for constants).
Reviewed By: skcho
Differential Revision: D23241457
fbshipit-source-id: 0da0b545c
Summary:
More scaffolding, nothing creates `Linear _` terms yet. Some changes to
variables substitution to allow substituting variables for linear terms
(as well as constants and other variables).
Reviewed By: skcho
Differential Revision: D23241461
fbshipit-source-id: fc870255e
Summary:
This is needed for the rest of the stack that introduces a `Linear of
LinArith.t` variant in `Term.t` to enable more normalisation inside of
terms.
Reviewed By: skcho
Differential Revision: D23241353
fbshipit-source-id: ad765cd13
Summary:
Make term simplification a bit more structured and separate the
"simplification" phase from the "evaluating constant expressions" phase.
Also implement the latter for all possible terms.
Reviewed By: skcho
Differential Revision: D23241334
fbshipit-source-id: 2964aa477
Summary: Not much to see here, extracted to make further changes more readable.
Reviewed By: da319
Differential Revision: D23241335
fbshipit-source-id: 81181f23a
Summary:
Since this is where almost all of the reasoning is concentrated, let's
make sure we use it at every opportunity!
Reviewed By: skcho
Differential Revision: D23194224
fbshipit-source-id: fedb2811e
Summary:
Reset the state before each test so that adding tests doesn't affect
other tests by shifting the ids of their anonymous variables.
Reviewed By: skcho
Differential Revision: D23194171
fbshipit-source-id: 7b717f160
Summary:
These are the only ones we need, it turns out the other types (string,
proc names, ...) were dead code. The changes the integer constants to
rational constants, to match the domain of the linear arithmetic engine.
Reviewed By: skcho
Differential Revision: D23164136
fbshipit-source-id: 755c3f526
Summary:
Instead of alternating between a normal form and a tree structure,
always keep a normal form. Except the normal form is not always fully
normalized. Overall, it's a bit faster than the previous iteration,
while being more precise! In particular, linear arithmetic aims at being
much more complete.
Reviewed By: skcho
Differential Revision: D23134209
fbshipit-source-id: 5f9ec6ece
Summary:
At the end of analysing a procedure we call `simplify
~keep:vars_live_in_pre_post`. Any variable not in
`vars_live_in_pre_post` is not mentioned anywhere else in the state and
therefore is not going to contribute constraints in callers of the
procedure (in other words: they're dead). We want to also forget
arithmetic facts about these variables as this is a good opportunity to
make the path condition smaller, sometimes by a lot!
The main issue is that dead variables may be useful intermediate terms
in the formula, eg trying to keep only facts about `x` in `y = x + 1 &&
y = 0` is going to lose a lot of precision. But, if a variable not in
`keep` is only mentioned in a simple atom `z = 42` atom, for example,
it's safe to forget about it, eg it's safe to remember only `x=0` in
`x=0 && z=42` (if only `x` is live).
In other words, we can get rid of all atoms containing variables not
transitively involved in other atoms that eventually involve live
variables. A graph problem! This is guaranteed not to forget anything
important and can still trim a lot of atoms in certain situations.
Reviewed By: skcho
Differential Revision: D22921313
fbshipit-source-id: 6d5db7cbe
Summary:
Perhaps a bit overkill to introduce all this extra complexity but it
makes the unit tests much more readable. In fact, this uncovered a bug
in the dead variable elimination!
Reviewed By: dulmarod
Differential Revision: D22925548
fbshipit-source-id: d1f411683
Summary:
Do not always add parens around sub-terms, and add more parens around
terms in atoms and normal forms when they can be confused with the atom
or normal form structure.
Reviewed By: skcho
Differential Revision: D22925549
fbshipit-source-id: 8646e96a5
Summary:
This time it's personal.
Roll out pulse's own arithmetic domain to be fast and be able to add
precision as needed. Formulas are precise representations of the path
condition to allow for good inter-procedural precision. Reasoning on
these is somewhat ad-hoc (except for equalities, but even these aren't
quite properly saturated in general), so expect lots of holes.
Skipping dead code in the interest of readability as this (at least
temporarily) doesn't use pudge anymore. This may make a come-back as
pudge has/will have better precision: the proposed implementation of
`PulseFormula` is very cheap so can be used any time we could want to
prune paths (see following commits), but this comes at the price of some
precision. Calling into pudge at reporting time still sounds like a good
idea to reduce false positives due to infeasible paths.
#skipdeadcode
Reviewed By: skcho
Differential Revision: D22576004
fbshipit-source-id: c91793256
Jules Villard