Tail duplication produces lots of identical phi nodes in different basic
blocks. Teach PHIElimination to reuse the join registers when lowering a phi
node that is identical to an already lowered node. This saves virtual
registers, and more importantly it avoids creating copies the the coalescer
doesn't know how to eliminate.

Teach LiveIntervalAnalysis about the phi joins with multiple uses.

This patch significantly reduces code size produced by -pre-regalloc-taildup.

llvm-svn: 91549

We want LiveVariables clients to use methods rather than accessing the
getVarInfo data structure directly. That way it will be possible to change the
LiveVariables representation.

llvm-svn: 90240

When splitting a critical edge, the registers live through the edge are:

- Used in a PHI instruction, or
- Live out from the predecessor, and
- Live in to the successor.

This allows the coalescer to eliminate even more phi joins.

llvm-svn: 89530

when LiveVariables is available.

The -split-phi-edges is now gone, and so is the hack to disable it when using
the local register allocator. The PHIElimination pass no longer has
LiveVariables as a prerequisite - that is what broke the local allocator.
Instead we do critical edge splitting when possible - that is when
LiveVariables is available.

llvm-svn: 89213

The BasicBlock associated with a MachineBasicBlock does not necessarily
correspond to the code in the MBB.

Don't insert a new IR BasicBlock when splitting critical edges. We are not
supposed to modify the IR during codegen, and we should be able to do just
fine with a NULL BB.

llvm-svn: 88707

- Edges are split before any phis are eliminated, so the code is SSA.

- Create a proper IR BasicBlock for the split edges.

- LiveVariables::addNewBlock now has same syntax as
  MachineDominatorTree::addNewBlock. Algorithm calculates predecessor live-out
  set rather than successor live-in set.

This feature still causes some miscompilations.

llvm-svn: 86867

Critical edges leading to a PHI node are split when the PHI source variable is
live out from the predecessor block. This help the coalescer eliminate more
PHI joins.

llvm-svn: 86725

Clean up some whitespace.
No functional changes.

llvm-svn: 86724

llvm-svn: 80993

llvm-svn: 76849

llvm-svn: 76688