[LLVMdev] SSI and ABCD for LLVM

[Duncan Sands]

Hi André,

> we chose ABCD because it is a fast approach to solve the problem. It has 
> the drawback that it is intra-procedural. For the Summer of Code 
> project, we will stick to the original ABCD algorithm. But we can study 
> modifications to make it inter-procedural for later research. Any ideas 
> and contributions you might have will be welcome.

there is a plan to replace the zext and sext parameter attributes with
attributes that tell you how many top bits are zero / sign extended.
For example, if an i32 parameter is marked with the "zext from i27"
attribute that means that the upper 5 bits are always zero.  Your
proposed pass to calculate which bits are in use could both use this
information and calculate it.  This is also gives some info useful
for bounds checking.  It might also be useful to extend these attributes
to give more precise range information on parameters.  Then the ABCD
algorithm could set and use them, giving a cheap form of
inter-procedural ABCD.

Ciao,

Duncan.