Move the Target way of overriding DAG Scheduler to a target hook

Summary:
The previous way of overriding it was relying on calling "setDefault"
on the global registry, which implies global mutable state.

Reviewers: echristo, atrick

Subscribers: llvm-commits

Differential Revision: http://reviews.llvm.org/D11538

From: Mehdi Amini <mehdi.amini@apple.com>
llvm-svn: 243388

3 files changed, 12 insertions, 14 deletions

diff --git a/llvm/include/llvm/CodeGen/SchedulerRegistry.h b/llvm/include/llvm/CodeGen/SchedulerRegistry.h
index 51ac7f28527..a7a6227664d 100644
--- a/llvm/include/llvm/CodeGen/SchedulerRegistry.h
+++ b/llvm/include/llvm/CodeGen/SchedulerRegistry.h
@@ -52,12 +52,6 @@ public:
   static RegisterScheduler *getList() {
     return (RegisterScheduler *)Registry.getList();
   }
-  static FunctionPassCtor getDefault() {
-    return (FunctionPassCtor)Registry.getDefault();
-  }
-  static void setDefault(FunctionPassCtor C) {
-    Registry.setDefault((MachinePassCtor)C);
-  }
   static void setListener(MachinePassRegistryListener *L) {
     Registry.setListener(L);
   }
diff --git a/llvm/include/llvm/Target/TargetSubtargetInfo.h b/llvm/include/llvm/Target/TargetSubtargetInfo.h
index 07c0c66bfa1..d50aa4932f8 100644
--- a/llvm/include/llvm/Target/TargetSubtargetInfo.h
+++ b/llvm/include/llvm/Target/TargetSubtargetInfo.h
@@ -15,6 +15,7 @@
 #define LLVM_TARGET_TARGETSUBTARGETINFO_H
 
 #include "llvm/CodeGen/PBQPRAConstraint.h"
+#include "llvm/CodeGen/SchedulerRegistry.h"
 #include "llvm/MC/MCSubtargetInfo.h"
 #include "llvm/Support/CodeGen.h"
 
@@ -81,6 +82,11 @@ public:
   virtual const TargetSelectionDAGInfo *getSelectionDAGInfo() const {
     return nullptr;
   }
+  /// Target can subclass this hook to select a different DAG scheduler.
+  virtual RegisterScheduler::FunctionPassCtor
+      getDAGScheduler(CodeGenOpt::Level) const {
+    return nullptr;
+  }
 
   /// getRegisterInfo - If register information is available, return it.  If
   /// not, return null.  This is kept separate from RegInfo until RegInfo has
diff --git a/llvm/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp b/llvm/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp
index c3dab9cc293..6b5fcb095e2 100644
--- a/llvm/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp
@@ -293,6 +293,11 @@ namespace llvm {
     const TargetLowering *TLI = IS->TLI;
     const TargetSubtargetInfo &ST = IS->MF->getSubtarget();
 
+    // Try first to see if the Target has its own way of selecting a scheduler
+    if (auto *SchedulerCtor = ST.getDAGScheduler(OptLevel)) {
+      return SchedulerCtor(IS, OptLevel);
+    }
+
     if (OptLevel == CodeGenOpt::None ||
         (ST.enableMachineScheduler() && ST.enableMachineSchedDefaultSched()) ||
         TLI->getSchedulingPreference() == Sched::Source)
@@ -1643,14 +1648,7 @@ SelectionDAGISel::FinishBasicBlock() {
 /// one preferred by the target.
 ///
 ScheduleDAGSDNodes *SelectionDAGISel::CreateScheduler() {
-  RegisterScheduler::FunctionPassCtor Ctor = RegisterScheduler::getDefault();
-
-  if (!Ctor) {
-    Ctor = ISHeuristic;
-    RegisterScheduler::setDefault(Ctor);
-  }
-
-  return Ctor(this, OptLevel);
+  return ISHeuristic(this, OptLevel);
 }
 
 //===----------------------------------------------------------------------===//