[TTI] Add getInliningThresholdMultiplier.

Summary:
InlineCost's threshold is multiplied by this value.  This lets us adjust
the inlining threshold up or down on a per-target basis.  For example,
we might want to increase the threshold on targets where calls are
unusually expensive.

Reviewers: chandlerc

Subscribers: llvm-commits

Differential Revision: http://reviews.llvm.org/D18560

llvm-svn: 266405

llvm/include/llvm/Analysis/TargetTransformInfo.h

@@ -166,6 +166,14 @@ public:
   /// This overload allows specifying a set of candidate argument values.
   int getCallCost(const Function *F, ArrayRef<const Value *> Arguments) const;
 
+  /// \returns A value by which our inlining threshold should be multiplied.
+  /// This is primarily used to bump up the inlining threshold wholesale on
+  /// targets where calls are unusually expensive.
+  ///
+  /// TODO: This is a rather blunt instrument.  Perhaps altering the costs of
+  /// individual classes of instructions would be better.
+  unsigned getInliningThresholdMultiplier() const;
+
   /// \brief Estimate the cost of an intrinsic when lowered.
   ///
   /// Mirrors the \c getCallCost method but uses an intrinsic identifier.
@@ -600,6 +608,7 @@ public:
   virtual int getCallCost(const Function *F, int NumArgs) = 0;
   virtual int getCallCost(const Function *F,
                           ArrayRef<const Value *> Arguments) = 0;
+  virtual unsigned getInliningThresholdMultiplier() = 0;
   virtual int getIntrinsicCost(Intrinsic::ID IID, Type *RetTy,
                                ArrayRef<Type *> ParamTys) = 0;
   virtual int getIntrinsicCost(Intrinsic::ID IID, Type *RetTy,
@@ -722,6 +731,9 @@ public:
                   ArrayRef<const Value *> Arguments) override {
     return Impl.getCallCost(F, Arguments);
   }
+  unsigned getInliningThresholdMultiplier() override {
+    return Impl.getInliningThresholdMultiplier();
+  }
   int getIntrinsicCost(Intrinsic::ID IID, Type *RetTy,
                        ArrayRef<Type *> ParamTys) override {
     return Impl.getIntrinsicCost(IID, RetTy, ParamTys);

llvm/include/llvm/Analysis/TargetTransformInfoImpl.h

@@ -128,6 +128,8 @@ public:
     return TTI::TCC_Basic * (NumArgs + 1);
   }
 
+  unsigned getInliningThresholdMultiplier() { return 1; }
+
   unsigned getIntrinsicCost(Intrinsic::ID IID, Type *RetTy,
                             ArrayRef<Type *> ParamTys) {
     switch (IID) {

llvm/include/llvm/CodeGen/BasicTTIImpl.h

@@ -216,6 +216,8 @@ public:
     return BaseT::getOperationCost(Opcode, Ty, OpTy);
   }
 
+  unsigned getInliningThresholdMultiplier() { return 1; }
+
   void getUnrollingPreferences(Loop *L, TTI::UnrollingPreferences &UP) {
     // This unrolling functionality is target independent, but to provide some
     // motivation for its intended use, for x86:

llvm/lib/Analysis/InlineCost.cpp

@@ -655,6 +655,10 @@ void CallAnalyzer::updateThreshold(CallSite CS, Function &Callee) {
        ColdThreshold.getNumOccurrences() > 0) &&
       ColdCallee && ColdThreshold < Threshold)
     Threshold = ColdThreshold;
+
+  // Finally, take the target-specific inlining threshold multiplier into
+  // account.
+  Threshold *= TTI.getInliningThresholdMultiplier();
 }
 
 bool CallAnalyzer::visitCmpInst(CmpInst &I) {

llvm/lib/Analysis/TargetTransformInfo.cpp

@@ -66,6 +66,10 @@ int TargetTransformInfo::getCallCost(const Function *F,
   return Cost;
 }
 
+unsigned TargetTransformInfo::getInliningThresholdMultiplier() const {
+  return TTIImpl->getInliningThresholdMultiplier();
+}
+
 int TargetTransformInfo::getIntrinsicCost(
     Intrinsic::ID IID, Type *RetTy, ArrayRef<const Value *> Arguments) const {
   int Cost = TTIImpl->getIntrinsicCost(IID, RetTy, Arguments);