Implement rdar://6295824 and PR6724 with two tiny changes

that can have a big effect :).  The first is to enable the
iterative SCC passmanager juice that kicks in when the
scc passmgr detects that a function pass has devirtualized
a call.  In this case, it will rerun all the passes it 
manages on the SCC, up to the iteration count limit (4). This
is useful because a function pass may devirualize a call, and
we want the inliner to inline it, or pruneeh to infer stuff
about it, etc.

The second patch is to add *all* call sites to the 
DevirtualizedCalls list the inliner uses.  This list is
about to get renamed, but the jist of this is that the 
inliner now reconsiders *all* inlined call sites as candidates
for further inlining.  The intuition is this that in cases 
like this:

f() { g(1); }     g(int x) { h(x); }

We analyze this bottom up, and may decide that it isn't 
profitable to inline H into G.  Next step, we decide that it is
profitable to inline G into F, and do so, which means that F 
now calls H.  Even though the call from G -> H may not have been
profitable to inline, the call from F -> H may be (in this case
because a constant allows folding etc).

In my spot checks, this doesn't have a big impact on code.  For
example, the LLC output for 252.eon grew from 0.02% (from
317252 to 317308) and 176.gcc actually shrunk by .3% (from 1525612
to 1520964 bytes).  252.eon never iterated in the SCC Passmgr,
176.gcc iterated at most 1 time.

llvm-svn: 102823

1 files changed, 1 insertions, 1 deletions

diff --git a/llvm/lib/Analysis/IPA/CallGraphSCCPass.cpp b/llvm/lib/Analysis/IPA/CallGraphSCCPass.cpp
index 917aa990ceb..288a7ef1583 100644
--- a/llvm/lib/Analysis/IPA/CallGraphSCCPass.cpp
+++ b/llvm/lib/Analysis/IPA/CallGraphSCCPass.cpp
@@ -30,7 +30,7 @@
 using namespace llvm;
 
 static cl::opt<unsigned> 
-MaxIterations("max-cg-scc-iterations", cl::ReallyHidden, cl::init(0));
+MaxIterations("max-cg-scc-iterations", cl::ReallyHidden, cl::init(4));
 
 STATISTIC(MaxSCCIterations, "Maximum CGSCCPassMgr iterations on one SCC");