Support Signed Lifted IL Shift Amounts in Custom Architectures

[ehntoo]

What is the feature you'd like to have?
Support negative/signed shift amounts in arithmetic and logical shifts. At present, an IL arithmetic shift right with a shift amount of 0xFFFFFFFF on a 32-bit architecture results in an attempted shift of val >> 4294967295, resulting in a value filled with whatever the upper-most bit was. I would like to see either additional Lifted IL operations that accept a signed shift amount, or to have the existing Lifted IL operations interpret the shift amount argument as a signed value, with corresponding documented semantics.

Is your feature request related to a problem?
Hexagon provides arithmetic and logical shift operations for both left- and right- shifts that take a shift amount from a register. The architecture defines the semantics for a negative shift amount as a shift of the same type (arithmetic or logical) in the opposite direction. This is presently somewhat tricky to lift, and would introduce additional conditionals into the IL flow for every shift operation of this type.

[galenbwill]

To make this concrete, please add example hexagon assembly, the LLIL you're lifting it to, and the resulting MLIL.

[plafosse]

The workaround here in the meant time would be to add a condition if <0 invert the shift direction, which could cause some pretty ugly lifting if this is like part of an array calculation.