[MachineOutliner] Add support for target-default outlining.

This adds functionality to the outliner that allows targets to
specify certain functions that should be outlined from by default.

If a target supports default outlining, then it specifies that in
its TargetOptions. In the case that it does, and the user hasn't
specified that they *never* want to outline, the outliner will
be added to the pass pipeline and will run on those default functions.

This is a preliminary patch for turning the outliner on by default
under -Oz for AArch64.

https://reviews.llvm.org/D48776

llvm-svn: 336040

1 files changed, 27 insertions, 2 deletions

diff --git a/llvm/lib/CodeGen/MachineOutliner.cpp b/llvm/lib/CodeGen/MachineOutliner.cpp
index 8e92cd4..da084d9 100644
--- a/llvm/lib/CodeGen/MachineOutliner.cpp
+++ b/llvm/lib/CodeGen/MachineOutliner.cpp
@@ -688,6 +688,12 @@ struct MachineOutliner : public ModulePass {
   /// linkonceodr linkage.
   bool OutlineFromLinkOnceODRs = false;
 
+  /// Set to true if the outliner should run on all functions in the module
+  /// considered safe for outlining.
+  /// Set to true by default for compatibility with llc's -run-pass option.
+  /// Set when the pass is constructed in TargetPassConfig.
+  bool RunOnAllFunctions = true;
+
   // Collection of IR functions created by the outliner.
   std::vector<Function *> CreatedIRFunctions;
 
@@ -806,8 +812,10 @@ struct MachineOutliner : public ModulePass {
 char MachineOutliner::ID = 0;
 
 namespace llvm {
-ModulePass *createMachineOutlinerPass() {
-  return new MachineOutliner();
+ModulePass *createMachineOutlinerPass(bool RunOnAllFunctions) {
+  MachineOutliner *OL = new MachineOutliner();
+  OL->RunOnAllFunctions = RunOnAllFunctions;
+  return OL;
 }
 
 } // namespace llvm
@@ -1331,6 +1339,20 @@ bool MachineOutliner::runOnModule(Module &M) {
   const TargetRegisterInfo *TRI = STI.getRegisterInfo();
   const TargetInstrInfo *TII = STI.getInstrInfo();
 
+  // If the user passed -enable-machine-outliner=always or
+  // -enable-machine-outliner, the pass will run on all functions in the module.
+  // Otherwise, if the target supports default outlining, it will run on all
+  // functions deemed by the target to be worth outlining from by default. Tell
+  // the user how the outliner is running.
+  LLVM_DEBUG(
+    dbgs() << "Machine Outliner: Running on ";
+    if (RunOnAllFunctions)
+      dbgs() << "all functions";
+    else
+      dbgs() << "target-default functions";
+    dbgs() << "\n"
+  );
+
   // If the user specifies that they want to outline from linkonceodrs, set
   // it here.
   OutlineFromLinkOnceODRs = EnableLinkOnceODROutlining;
@@ -1355,6 +1377,9 @@ bool MachineOutliner::runOnModule(Module &M) {
     if (!MF)
       continue;
 
+    if (!RunOnAllFunctions && !TII->shouldOutlineFromFunctionByDefault(*MF))
+      continue;
+
     // We have a MachineFunction. Ask the target if it's suitable for outlining.
     // If it isn't, then move on to the next Function in the module.
     if (!TII->isFunctionSafeToOutlineFrom(*MF, OutlineFromLinkOnceODRs))