Provide a place for targets to insert ILP optimization passes.

Move the early if-conversion pass into this group.

ILP optimizations usually need to find the right balance between
register pressure and ILP using the MachineTraceMetrics analysis to
identify critical paths and estimate other costs. Such passes should run
together so they can share dominator tree and loop info analyses.

Besides if-conversion, future passes to run here here could include
expression height reduction and ARM's MLxExpansion pass.

llvm-svn: 172687

include/llvm/CodeGen/Passes.h

@@ -181,6 +181,16 @@ protected:
   /// instructions in SSA form.
   virtual void addMachineSSAOptimization();
 
+  /// Add passes that optimize instruction level parallelism for out-of-order
+  /// targets. These passes are run while the machine code is still in SSA
+  /// form, so they can use MachineTraceMetrics to control their heuristics.
+  ///
+  /// All passes added here should preserve the MachineDominatorTree,
+  /// MachineLoopInfo, and MachineTraceMetrics analyses.
+  virtual bool addILPOpts() {
+    return false;
+  }
+
   /// addPreRegAlloc - This method may be implemented by targets that want to
   /// run passes immediately before register allocation. This should return
   /// true if -print-machineinstrs should print after these passes.

lib/CodeGen/Passes.cpp

@@ -238,9 +238,6 @@ TargetPassConfig::TargetPassConfig(TargetMachine *tm, PassManagerBase &pm)
   substitutePass(&EarlyTailDuplicateID, &TailDuplicateID);
   substitutePass(&PostRAMachineLICMID, &MachineLICMID);
 
-  // Disable early if-conversion. Targets that are ready can enable it.
-  disablePass(&EarlyIfConverterID);
-
   // Temporarily disable experimental passes.
   const TargetSubtargetInfo &ST = TM->getSubtarget<TargetSubtargetInfo>();
   if (!ST.enableMachineScheduler())
@@ -551,7 +548,12 @@ void TargetPassConfig::addMachineSSAOptimization() {
   addPass(&DeadMachineInstructionElimID);
   printAndVerify("After codegen DCE pass");
 
-  addPass(&EarlyIfConverterID);
+  // Allow targets to insert passes that improve instruction level parallelism,
+  // like if-conversion. Such passes will typically need dominator trees and
+  // loop info, just like LICM and CSE below.
+  if (addILPOpts())
+    printAndVerify("After ILP optimizations");
+
   addPass(&MachineLICMID);
   addPass(&MachineCSEID);
   addPass(&MachineSinkingID);

lib/Target/X86/X86TargetMachine.cpp

@@ -151,6 +151,7 @@ public:
   }
 
   virtual bool addInstSelector();
+  virtual bool addILPOpts();
   virtual bool addPreRegAlloc();
   virtual bool addPostRegAlloc();
   virtual bool addPreEmitPass();
@@ -158,12 +159,7 @@ public:
 } // namespace
 
 TargetPassConfig *X86TargetMachine::createPassConfig(PassManagerBase &PM) {
-  X86PassConfig *PC = new X86PassConfig(this, PM);
-
-  if (X86EarlyIfConv && Subtarget.hasCMov())
-    PC->enablePass(&EarlyIfConverterID);
-
-  return PC;
+  return new X86PassConfig(this, PM);
 }
 
 bool X86PassConfig::addInstSelector() {
@@ -181,6 +177,14 @@ bool X86PassConfig::addInstSelector() {
   return false;
 }
 
+bool X86PassConfig::addILPOpts() {
+  if (X86EarlyIfConv && getX86Subtarget().hasCMov()) {
+    addPass(&EarlyIfConverterID);
+    return true;
+  }
+  return false;
+}
+
 bool X86PassConfig::addPreRegAlloc() {
   return false;  // -print-machineinstr shouldn't print after this.
 }