RegAlloc superpass: includes phi elimination, coalescing, and scheduling.

Creates a configurable regalloc pipeline.

Ensure specific llc options do what they say and nothing more: -reglloc=... has no effect other than selecting the allocator pass itself. This patch introduces a new umbrella flag, "-optimize-regalloc", to enable/disable the optimizing regalloc "superpass". This allows for example testing coalscing and scheduling under -O0 or vice-versa.

When a CodeGen pass requires the MachineFunction to have a particular property, we need to explicitly define that property so it can be directly queried rather than naming a specific Pass. For example, to check for SSA, use MRI->isSSA, not addRequired<PHIElimination>.

CodeGen transformation passes are never "required" as an analysis

ProcessImplicitDefs does not require LiveVariables.

We have a plan to massively simplify some of the early passes within the regalloc superpass.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@150226 91177308-0d34-0410-b5e6-96231b3b80d8

lib/CodeGen/PHIElimination.cpp

@@ -92,11 +92,15 @@ STATISTIC(NumCriticalEdgesSplit, "Number of critical edges split");
 STATISTIC(NumReused, "Number of reused lowered phis");
 
 char PHIElimination::ID = 0;
-INITIALIZE_PASS(PHIElimination, "phi-node-elimination",
-                "Eliminate PHI nodes for register allocation", false, false)
-
 char& llvm::PHIEliminationID = PHIElimination::ID;
 
+INITIALIZE_PASS_BEGIN(PHIElimination, "phi-node-elimination",
+                      "Eliminate PHI nodes for register allocation",
+                      false, false)
+INITIALIZE_PASS_DEPENDENCY(LiveVariables)
+INITIALIZE_PASS_END(PHIElimination, "phi-node-elimination",
+                    "Eliminate PHI nodes for register allocation", false, false)
+
 void PHIElimination::getAnalysisUsage(AnalysisUsage &AU) const {
   AU.addPreserved<LiveVariables>();
   AU.addPreserved<MachineDominatorTree>();