[PowerPC] Add a flag for experimenting with subreg liveness tracking

This cannot yet be enabled by default, it causes ~50 miscompiles in the test
suite.

llvm-svn: 225497

llvm/lib/Target/PowerPC/PPCSubtarget.cpp

@@ -19,6 +19,7 @@
 #include "llvm/IR/Attributes.h"
 #include "llvm/IR/Function.h"
 #include "llvm/IR/GlobalValue.h"
+#include "llvm/Support/CommandLine.h"
 #include "llvm/Support/Host.h"
 #include "llvm/Support/TargetRegistry.h"
 #include "llvm/Target/TargetMachine.h"
@@ -32,6 +33,9 @@ using namespace llvm;
 #define GET_SUBTARGETINFO_CTOR
 #include "PPCGenSubtargetInfo.inc"
 
+static cl::opt<bool> UseSubRegLiveness("ppc-track-subreg-liveness",
+cl::desc("Enable subregister liveness tracking for PPC"), cl::Hidden);
+
 /// Return the datalayout string of a subtarget.
 static std::string getDataLayoutString(const Triple &T) {
   bool is64Bit = T.getArch() == Triple::ppc64 || T.getArch() == Triple::ppc64le;
@@ -234,3 +238,7 @@ bool PPCSubtarget::useAA() const {
   return needsAggressiveScheduling(DarwinDirective);
 }
 
+bool PPCSubtarget::enableSubRegLiveness() const {
+  return UseSubRegLiveness;
+}
+

llvm/lib/Target/PowerPC/PPCSubtarget.h

@@ -259,6 +259,8 @@ public:
                            MachineInstr *end,
                            unsigned NumRegionInstrs) const override;
   bool useAA() const override;
+
+  bool enableSubRegLiveness() const override;
 };
 } // End llvm namespace