SMT: Add property and counterexample directive

Rather than generating SMT from a function called check_sat, now find
any function with a $property directive and generate SMT for it, e.g.

$property
function prop_cap_round_trip(cap: bits(128)) -> bool = {
  let cap_rt = capToBits(capBitsToCapability(true, cap));
  cap == cap_rt
}

$property
function prop_base_lteq_top(capbits: bits(128)) -> bool = {
  let c = capBitsToCapability(true, capbits);
  let (base, top) = getCapBounds(c);
  let e = unsigned(c.E);
  e >= 51 | base <= top
}

The file property.ml has a function for gathering all the properties
in a file, as well as a rewrite-pass for properties with type
quantifiers, which allows us to handle properties like

function prop forall 'n, 'n <= 100. (bv: bits('n)) -> bool = exp

by rewriting to (conceptually)

function prop(bv: bits(MAX_BIT_WIDTH)) -> bool =
  if length(bv) > 100 then true else exp

The function return is now automatically negated (i.e. always true =
unsat, sometimes false = sat), which makes sense for quickcheck-type
properties.

1 files changed, 4 insertions, 3 deletions

diff --git a/test/smt/rv_add_decode.unsat.sail b/test/smt/rv_add_decode.unsat.sail
index d5952e09..01653c6f 100644
--- a/test/smt/rv_add_decode.unsat.sail
+++ b/test/smt/rv_add_decode.unsat.sail
@@ -17,9 +17,10 @@ function clause decode imm : bits(12) @ rs1 : regbits @ 0b000 @ rd : regbits @ 0
 
 function clause decode _ = None()
 
-function check_sat(imm:  bits(12), rs1: regbits, rd: regbits) -> bool = {
+$property
+function prop(imm:  bits(12), rs1: regbits, rd: regbits) -> bool = {
   match decode(imm @ rs1 @ 0b000 @ rd @ 0b0010011) {
-    Some(ITYPE(_)) => false,
-    _ => true
+    Some(ITYPE(_)) => true,
+    _ => false
   }
 }
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