Jonas Jensen 033a4c30ea C++: Fix perf of IR value numbering ...

On some snapshots, notably ffmpeg, the IR `ValueNumbering` recursion
would generate billions of tuples and eventually run out of space.

It turns out it was fairly common for an `Instruction` to get more than
one `ValueNumber` in the base cases for `VariableAddressInstruction` and
`InitializeParameterInstruction`, and it could also happen in an
instruction with more than one operand of the same `OperandTag`. When a
binary operation was applied to an instruction with `m` value numbers
and another instruction with `n` value numbers, the result would get
`m * n` value numbers. This led to doubly-exponential growth in the
number of value numbers in rare cases.

The underlying reason why a `VariableAddressInstruction` could get
multiple value numbers is that it was keyed on the associated
`IRVariable`, and the `IRVariable` is defined in part by the type of its
underlying `Variable` (or other AST element). If the extractor defines a
variable to have multiple types because of linker ambiguity, this leads
to the creation of multiple `IRVariable`s. That should ideally be solved
in `TIRVariable.qll`, but for now I've put a workaround in
`ValueNumberingInternal.qll` instead.

To remove the problem with instructions having multiple operands, the
construction in `Operand.qll` will now filter out any such operand. It
wasn't enough to apply that filter to the `raw` stage, so I've applied
it to all three stages.

2020-02-12 14:38:41 +01:00

..

examples

CPP: Autoformat cookbook examples.

2019-08-02 15:29:20 +02:00

src

C++: Fix perf of IR value numbering

2020-02-12 14:38:41 +01:00

test

C++: Understand formatting function varargs as needing null termination.

2020-02-11 15:25:59 +00:00