This pass is dedicated to applying a bunch of peephole optimizations
that are useful for decompilation and haven't been implemented in LLVM
for whatever reason.
At the moment it only runs an optimization that tries to reduce the uses
of incoming values of PHINodes, under very specific condidtions, which
enables emitting less LocalVariables.
Before this commit, many passes in revng-c were skipping over
non-isolated functions.
Now revng-pipeline takes care of removing non-isolated functions so that
check can be omitted everywhere.
Over time, these tags have shifted to basically coincide with the Copy
and Assign tags. There's no need for them anymore they just make the
code more verbose and less straightforward.
Before this commit the `hasSideEffects` helper function was only a stub,
that was never updated to be aware of recent FunctionTags representing
custom opcodes without side-effects.
This commit updates it, so that now it is less aggressive in marking
harmless stuff as side-effectful.
This commits changes the ExitSSAPass to ensure that StoreInst are placed
ASAP, close to the computation of the incoming Values of the replaced
PHINode.
This generates IR that typically yields less local variables in
SwitchToStatements.
Various parts of revng replace `llvm::GlobalVariable`s representing CSVs
with Allocal/Load/Store. In particular, these are PromoteCSV,
RootAnalyzer and PromoteGlobalToLocalVars.
Before this commit, those places were sloppy when replacing CSVs with
Alloca/Load/Store, and did that iterating on a container sorted by
pointers. This caused Alloca/Load/Store to be emitted in different order
accross runs, which in turn caused more non-determinism down the
pipeline.
This commit fixes the non-deterministic behavior, sorting CSVs based on
their names, which should always be present and deterministic.
This lets up cleanly "bail out" after only some of the computation
is done. This way we avoid reading information we don't really use
from the model based on who is the specific user of the oracle.
This commit moves stuff around to enforce complete information being
present by the time the "Internal" assembly output is ready.
Because of that, the "Internal" format needed to change, now it uses
tag representation close to PTML as opposed to the one close to LLVM's
used before now.
This change slightly improves the performance on slow to medium graphs
while leaving the performance on somewhat big ones untouched and
making the extremely big ones a lot worse. It also greatly improves
performance in the general case.
Pietro Fezzardi