Add an experimental -early-live-intervals option.

This option runs LiveIntervals before TwoAddressInstructionPass which
will eventually learn to exploit and update the analysis.

Eventually, LiveIntervals will run before PHIElimination, and we can get
rid of LiveVariables.

llvm-svn: 161270

2 files changed, 10 insertions, 0 deletions

diff --git a/llvm/lib/CodeGen/LiveIntervalAnalysis.cpp b/llvm/lib/CodeGen/LiveIntervalAnalysis.cpp
index b488e8f077e..d0f8ae1af30 100644
--- a/llvm/lib/CodeGen/LiveIntervalAnalysis.cpp
+++ b/llvm/lib/CodeGen/LiveIntervalAnalysis.cpp
@@ -45,6 +45,7 @@ NewLiveIntervals("new-live-intervals", cl::Hidden,
                  cl::desc("Use new algorithm forcomputing live intervals"));
 
 char LiveIntervals::ID = 0;
+char &llvm::LiveIntervalsID = LiveIntervals::ID;
 INITIALIZE_PASS_BEGIN(LiveIntervals, "liveintervals",
                 "Live Interval Analysis", false, false)
 INITIALIZE_AG_DEPENDENCY(AliasAnalysis)
diff --git a/llvm/lib/CodeGen/Passes.cpp b/llvm/lib/CodeGen/Passes.cpp
index 69d6d00091a..cfa3eecf02e 100644
--- a/llvm/lib/CodeGen/Passes.cpp
+++ b/llvm/lib/CodeGen/Passes.cpp
@@ -88,6 +88,10 @@ PrintMachineInstrs("print-machineinstrs", cl::ValueOptional,
                    cl::desc("Print machine instrs"),
                    cl::value_desc("pass-name"), cl::init("option-unspecified"));
 
+// Experimental option to run live inteerval analysis early.
+static cl::opt<bool> EarlyLiveIntervals("early-live-intervals", cl::Hidden,
+    cl::desc("Run live interval analysis earlier in the pipeline"));
+
 /// Allow standard passes to be disabled by command line options. This supports
 /// simple binary flags that either suppress the pass or do nothing.
 /// i.e. -disable-mypass=false has no effect.
@@ -648,6 +652,11 @@ void TargetPassConfig::addOptimizedRegAlloc(FunctionPass *RegAllocPass) {
     addPass(&MachineLoopInfoID);
     addPass(&PHIEliminationID);
   }
+
+  // Eventually, we want to run LiveIntervals before PHI elimination.
+  if (EarlyLiveIntervals)
+    addPass(&LiveIntervalsID);
+
   addPass(&TwoAddressInstructionPassID);
 
   if (EnableStrongPHIElim)