llvm dev - May 2011 - [LLVMdev] Reg2mem: Identifying introduced memory locations (also, what happens to the phi nodes)

Hi.

Im exploring `opt -reg2mem` output for a simple C program (actually,
that is this snippet:
http://rosettacode.org/wiki/Dining_philosophers#C - compiled with
clang -O1) and got two questions regarding this pass.

1. How would I tell which memory locations were introduced by the
pass, and which memory locations were present in the original program?
After a brief diffing of .ll files, I'd suppose that introduced
"alloca"s would put their result in a variable named
"somename.reg2mem". But is the ".reg2mem" suffix a reliable
way to
identify introduced allocas?

2. There seems to be no "phi" instructions after the pass. Does the
pass always remove all "phi" instructions?

Hi Alexey,
> 1. How would I tell which memory locations were introduced by the
> pass, and which memory locations were present in the original program?
> After a brief diffing of .ll files, I'd suppose that introduced
> "alloca"s would put their result in a variable named
> "somename.reg2mem". But is the ".reg2mem" suffix a
reliable way to
> identify introduced allocas?
as a general rule you shouldn't make any use of names.  For example,
it is perfectly possible for instructions to have no names.
> 2. There seems to be no "phi" instructions after the pass. Does
the
> pass always remove all "phi" instructions?
I believe so.  In fact I think that's the point of this pass.

Ciao, Duncan.