Rework of the new interface for shrink wrapping

Based on comments from Hal
(http://lists.llvm.org/pipermail/llvm-commits/Week-of-Mon-20150810/292978.html),
I've changed the interface to add a callback mechanism to the
TargetFrameLowering class to query whether the specific target
supports shrink wrapping.  By default, shrink wrapping is disabled by
default. Each target can override the default behaviour using the
TargetFrameLowering::targetSupportsShrinkWrapping() method. Shrink
wrapping can still be explicitly enabled or disabled from the command
line, using the existing -enable-shrink-wrap=<true|false> option.

Phabricator: http://reviews.llvm.org/D12293


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@246463 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/CodeGen/Passes.h

@@ -120,9 +120,6 @@ protected:
   /// Default setting for -enable-tail-merge on this target.
   bool EnableTailMerge;
 
-  /// Default setting for -enable-shrink-wrap on this target.
-  bool EnableShrinkWrap;
-
 public:
   TargetPassConfig(TargetMachine *tm, PassManagerBase &pm);
   // Dummy constructor.

include/llvm/Target/TargetFrameLowering.h

@@ -141,6 +141,11 @@ public:
     return false;
   }
 
+  /// Returns true if the target will correctly handle shrink wrapping.
+  virtual bool enableShrinkWrapping(const MachineFunction &MF) const {
+    return false;
+  }
+  
   /// emitProlog/emitEpilog - These methods insert prolog and epilog code into
   /// the function.
   virtual void emitPrologue(MachineFunction &MF,

lib/CodeGen/Passes.cpp

@@ -56,9 +56,6 @@ static cl::opt<bool> DisableMachineLICM("disable-machine-licm", cl::Hidden,
     cl::desc("Disable Machine LICM"));
 static cl::opt<bool> DisableMachineCSE("disable-machine-cse", cl::Hidden,
     cl::desc("Disable Machine Common Subexpression Elimination"));
-static cl::opt<cl::boolOrDefault>
-    EnableShrinkWrapOpt("enable-shrink-wrap", cl::Hidden,
-                        cl::desc("enable the shrink-wrapping pass"));
 static cl::opt<cl::boolOrDefault> OptimizeRegAlloc(
     "optimize-regalloc", cl::Hidden,
     cl::desc("Enable optimized register allocation compilation path."));
@@ -221,7 +218,7 @@ TargetPassConfig::TargetPassConfig(TargetMachine *tm, PassManagerBase &pm)
     : ImmutablePass(ID), PM(&pm), StartBefore(nullptr), StartAfter(nullptr),
       StopAfter(nullptr), Started(true), Stopped(false),
       AddingMachinePasses(false), TM(tm), Impl(nullptr), Initialized(false),
-      DisableVerify(false), EnableTailMerge(true), EnableShrinkWrap(false) {
+      DisableVerify(false), EnableTailMerge(true) { 
 
   Impl = new PassConfigImpl();
 
@@ -543,8 +540,9 @@ void TargetPassConfig::addMachinePasses() {
   addPostRegAlloc();
 
   // Insert prolog/epilog code.  Eliminate abstract frame index references...
-  if (getEnableShrinkWrap())
+  if (getOptLevel() != CodeGenOpt::None) 
     addPass(&ShrinkWrapID);
+
   addPass(&PrologEpilogCodeInserterID);
 
   /// Add passes that optimize machine instructions after register allocation.
@@ -623,21 +621,6 @@ void TargetPassConfig::addMachineSSAOptimization() {
   addPass(&DeadMachineInstructionElimID);
 }
 
-bool TargetPassConfig::getEnableShrinkWrap() const {
-  switch (EnableShrinkWrapOpt) {
-  case cl::BOU_UNSET:
-    return EnableShrinkWrap && getOptLevel() != CodeGenOpt::None;
-  // If EnableShrinkWrap is set, it takes precedence on whatever the
-  // target sets. The rational is that we assume we want to test
-  // something related to shrink-wrapping.
-  case cl::BOU_TRUE:
-    return true;
-  case cl::BOU_FALSE:
-    return false;
-  }
-  llvm_unreachable("Invalid shrink-wrapping state");
-}
-
 //===---------------------------------------------------------------------===//
 /// Register Allocation Pass Configuration
 //===---------------------------------------------------------------------===//

lib/CodeGen/ShrinkWrap.cpp

@@ -78,6 +78,10 @@ STATISTIC(NumCandidates, "Number of shrink-wrapping candidates");
 STATISTIC(NumCandidatesDropped,
           "Number of shrink-wrapping candidates dropped because of frequency");
 
+static cl::opt<cl::boolOrDefault>
+    EnableShrinkWrapOpt("enable-shrink-wrap", cl::Hidden,
+                        cl::desc("enable the shrink-wrapping pass"));
+
 namespace {
 /// \brief Class to determine where the safe point to insert the
 /// prologue and epilogue are.
@@ -148,6 +152,9 @@ class ShrinkWrap : public MachineFunctionPass {
   /// shrink-wrapping.
   bool ArePointsInteresting() const { return Save != Entry && Save && Restore; }
 
+  /// \brief Check if shrink wrapping is enabled for this target and function.
+  static bool isShrinkWrapEnabled(const MachineFunction &MF);
+  
 public:
   static char ID;
 
@@ -319,8 +326,9 @@ void ShrinkWrap::updateSaveRestorePoints(MachineBasicBlock &MBB) {
 }
 
 bool ShrinkWrap::runOnMachineFunction(MachineFunction &MF) {
-  if (MF.empty())
+  if (MF.empty() || !isShrinkWrapEnabled(MF))
     return false;
+
   DEBUG(dbgs() << "**** Analysing " << MF.getName() << '\n');
 
   init(MF);
@@ -404,3 +412,20 @@ bool ShrinkWrap::runOnMachineFunction(MachineFunction &MF) {
   ++NumCandidates;
   return false;
 }
+
+bool ShrinkWrap::isShrinkWrapEnabled(const MachineFunction &MF) {
+  const TargetFrameLowering *TFI = MF.getSubtarget().getFrameLowering();
+
+  switch (EnableShrinkWrapOpt) {
+  case cl::BOU_UNSET:
+    return TFI->enableShrinkWrapping(MF);
+  // If EnableShrinkWrap is set, it takes precedence on whatever the
+  // target sets. The rational is that we assume we want to test
+  // something related to shrink-wrapping.
+  case cl::BOU_TRUE:
+    return true;
+  case cl::BOU_FALSE:
+    return false;
+  }
+  llvm_unreachable("Invalid shrink-wrapping state");
+}