Brian pointed out that the Olden/mst benchmark has code that basically looks
like this:

main() {
  Do_all_BlueRule(..., 1, 0);
}

void Do_all_BlueRule(..., int nproc, int pn) {
  if (nproc > 1) {
    Do_all_BlueRule(nproc/2, nproc/2+pn);
    ... A BUNCH OF OTHER STUFF ...
  }

  bar();
}

The observation is that Do_all_BlueRule contains a bunch of code that is
dynamically dead, but it requires a smarter IPCP algorithm to notice it (the
unreachable recursive call causes us to miss this).

It seems like an aggressive IPCP coupled with SCCP'y techniques could solve this
pretty easily.

-Chris

There are some notes for this bug here:
http://nondot.org/sabre/LLVMNotes/IP-SCCP.txt

-Chris

Here's a trivial testcase this should handle:

implementation   ; Functions:

internal int %foo(int %X) {
        %Y = call int %foo( int %X )            ; <int> [#uses=1]
        %Z = add int %Y, 1              ; <int> [#uses=1]
        ret int %Z
}

void %bar() {
        call int %foo( int 17 )         ; <int>:0 [#uses=0]
        ret void
}

IPCP should realize that %X is always '17'.  The current, simple IPCP, should
detect and handle this too.  I wish it already did, it would help pool
allocation. :(

-Chris

ok, another note.  Simple IPCP now handles the simple case above.

Initial implementation:
http://mail.cs.uiuc.edu/pipermail/llvm-commits/Week-of-Mon-20041206/022044.html

There is more to come for this PR, stay tuned!

-Chris

This is now implemented, named -ipsccp.

-Chris