Begin fleshing out an interface in TTI for modelling the costs of

generic function calls and intrinsics. This is somewhat overlapping with
an existing intrinsic cost method, but that one seems targetted at
vector intrinsics. I'll merge them or separate their names and use cases
in a separate commit.

This sinks the test of 'callIsSmall' down into TTI where targets can
control it. The whole thing feels very hack-ish to me though. I've left
a FIXME comment about the fundamental design problem this presents. It
isn't yet clear to me what the users of this function *really* care
about. I'll have to do more analysis to figure that out. Putting this
here at least provides it access to proper analysis pass tools and other
such. It also allows us to more cleanly implement the baseline cost
interfaces in TTI.

With this commit, it is now theoretically possible to simplify much of
the inline cost analysis's handling of calls by calling through to this
interface. That conversion will have to happen in subsequent commits as
it requires more extensive restructuring of the inline cost analysis.

The CodeMetrics class is now really only in the business of running over
a block of code and aggregating the metrics on that block of code, with
the actual cost evaluation done entirely in terms of TTI.

llvm-svn: 173148

Author: chandlerc

Diff for: llvm/include/llvm/Analysis/TargetTransformInfo.h

@@ -117,6 +117,41 @@ class TargetTransformInfo {
   virtual unsigned getGEPCost(const Value *Ptr,
                               ArrayRef<const Value *> Operands) const;
 
+  /// \brief Estimate the cost of a function call when lowered.
+  ///
+  /// The contract for this is the same as \c getOperationCost except that it
+  /// supports an interface that provides extra information specific to call
+  /// instructions.
+  ///
+  /// This is the most basic query for estimating call cost: it only knows the
+  /// function type and (potentially) the number of arguments at the call site.
+  /// The latter is only interesting for varargs function types.
+  virtual unsigned getCallCost(FunctionType *FTy, int NumArgs = -1) const;
+
+  /// \brief Estimate the cost of calling a specific function when lowered.
+  ///
+  /// This overload adds the ability to reason about the particular function
+  /// being called in the event it is a library call with special lowering.
+  virtual unsigned getCallCost(const Function *F, int NumArgs = -1) const;
+
+  /// \brief Estimate the cost of calling a specific function when lowered.
+  ///
+  /// This overload allows specifying a set of candidate argument values.
+  virtual unsigned getCallCost(const Function *F,
+                               ArrayRef<const Value *> Arguments) const;
+
+  /// \brief Estimate the cost of an intrinsic when lowered.
+  ///
+  /// Mirrors the \c getCallCost method but uses an intrinsic identifier.
+  virtual unsigned getIntrinsicCost(Intrinsic::ID IID, Type *RetTy,
+                                    ArrayRef<Type *> ParamTys) const;
+
+  /// \brief Estimate the cost of an intrinsic when lowered.
+  ///
+  /// Mirrors the \c getCallCost method but uses an intrinsic identifier.
+  virtual unsigned getIntrinsicCost(Intrinsic::ID IID, Type *RetTy,
+                                    ArrayRef<const Value *> Arguments) const;
+
   /// \brief Estimate the cost of a given IR user when lowered.
   ///
   /// This can estimate the cost of either a ConstantExpr or Instruction when
@@ -134,6 +169,20 @@ class TargetTransformInfo {
   /// comments for a detailed explanation of the cost values.
   virtual unsigned getUserCost(const User *U) const;
 
+  /// \brief Test whether calls to a function lower to actual program function
+  /// calls.
+  ///
+  /// The idea is to test whether the program is likely to require a 'call'
+  /// instruction or equivalent in order to call the given function.
+  ///
+  /// FIXME: It's not clear that this is a good or useful query API. Client's
+  /// should probably move to simpler cost metrics using the above.
+  /// Alternatively, we could split the cost interface into distinct code-size
+  /// and execution-speed costs. This would allow modelling the core of this
+  /// query more accurately as the a call is a single small instruction, but
+  /// incurs significant execution cost.
+  virtual bool isLoweredToCall(const Function *F) const;
+
   /// @}
 
   /// \name Scalar Target Information

Diff for: llvm/lib/Analysis/CodeMetrics.cpp

@@ -20,41 +20,6 @@
 
 using namespace llvm;
 
-/// callIsSmall - If a call is likely to lower to a single target instruction,
-/// or is otherwise deemed small return true.
-/// TODO: Perhaps calls like memcpy, strcpy, etc?
-bool llvm::callIsSmall(ImmutableCallSite CS) {
-  if (isa<IntrinsicInst>(CS.getInstruction()))
-    return true;
-
-  const Function *F = CS.getCalledFunction();
-  if (!F) return false;
-
-  if (F->hasLocalLinkage()) return false;
-
-  if (!F->hasName()) return false;
-
-  StringRef Name = F->getName();
-
-  // These will all likely lower to a single selection DAG node.
-  if (Name == "copysign" || Name == "copysignf" || Name == "copysignl" ||
-      Name == "fabs" || Name == "fabsf" || Name == "fabsl" ||
-      Name == "sin" || Name == "sinf" || Name == "sinl" ||
-      Name == "cos" || Name == "cosf" || Name == "cosl" ||
-      Name == "sqrt" || Name == "sqrtf" || Name == "sqrtl" )
-    return true;
-
-  // These are all likely to be optimized into something smaller.
-  if (Name == "pow" || Name == "powf" || Name == "powl" ||
-      Name == "exp2" || Name == "exp2l" || Name == "exp2f" ||
-      Name == "floor" || Name == "floorf" || Name == "ceil" ||
-      Name == "round" || Name == "ffs" || Name == "ffsl" ||
-      Name == "abs" || Name == "labs" || Name == "llabs")
-    return true;
-
-  return false;
-}
-
 /// analyzeBasicBlock - Fill in the current structure with information gleaned
 /// from the specified block.
 void CodeMetrics::analyzeBasicBlock(const BasicBlock *BB,
@@ -63,9 +28,6 @@ void CodeMetrics::analyzeBasicBlock(const BasicBlock *BB,
   unsigned NumInstsBeforeThisBB = NumInsts;
   for (BasicBlock::const_iterator II = BB->begin(), E = BB->end();
        II != E; ++II) {
-    if (TargetTransformInfo::TCC_Free == TTI.getUserCost(&*II))
-      continue;
-
     // Special handling for calls.
     if (isa<CallInst>(II) || isa<InvokeInst>(II)) {
       ImmutableCallSite CS(cast<Instruction>(II));
@@ -83,12 +45,10 @@ void CodeMetrics::analyzeBasicBlock(const BasicBlock *BB,
         // for that case.
         if (F == BB->getParent())
           isRecursive = true;
-      }
-
-      if (!callIsSmall(CS)) {
-        // Each argument to a call takes on average one instruction to set up.
-        NumInsts += CS.arg_size();
 
+        if (TTI.isLoweredToCall(F))
+          ++NumCalls;
+      } else {
         // We don't want inline asm to count as a call - that would prevent loop
         // unrolling. The argument setup cost is still real, though.
         if (!isa<InlineAsm>(CS.getCalledValue()))
@@ -112,7 +72,7 @@ void CodeMetrics::analyzeBasicBlock(const BasicBlock *BB,
       if (InvI->hasFnAttr(Attribute::NoDuplicate))
         notDuplicatable = true;
 
-    ++NumInsts;
+    NumInsts += TTI.getUserCost(&*II);
   }
 
   if (isa<ReturnInst>(BB->getTerminator()))

Diff for: llvm/lib/Analysis/IPA/InlineCost.cpp

@@ -736,7 +736,7 @@ bool CallAnalyzer::visitCallSite(CallSite CS) {
       return false;
     }
 
-    if (!callIsSmall(CS)) {
+    if (TTI.isLoweredToCall(F)) {
       // We account for the average 1 instruction per call argument setup
       // here.
       Cost += CS.arg_size() * InlineConstants::InstrCost;

Diff for: llvm/lib/Analysis/TargetTransformInfo.cpp

@@ -14,6 +14,7 @@
 #include "llvm/IR/Instruction.h"
 #include "llvm/IR/IntrinsicInst.h"
 #include "llvm/IR/Instructions.h"
+#include "llvm/Support/CallSite.h"
 #include "llvm/Support/ErrorHandling.h"
 
 using namespace llvm;
@@ -58,10 +59,39 @@ unsigned TargetTransformInfo::getGEPCost(
   return PrevTTI->getGEPCost(Ptr, Operands);
 }
 
+unsigned TargetTransformInfo::getCallCost(FunctionType *FTy,
+                                          int NumArgs) const {
+  return PrevTTI->getCallCost(FTy, NumArgs);
+}
+
+unsigned TargetTransformInfo::getCallCost(const Function *F,
+                                          int NumArgs) const {
+  return PrevTTI->getCallCost(F, NumArgs);
+}
+
+unsigned TargetTransformInfo::getCallCost(
+    const Function *F, ArrayRef<const Value *> Arguments) const {
+  return PrevTTI->getCallCost(F, Arguments);
+}
+
+unsigned TargetTransformInfo::getIntrinsicCost(
+    Intrinsic::ID IID, Type *RetTy, ArrayRef<Type *> ParamTys) const {
+  return PrevTTI->getIntrinsicCost(IID, RetTy, ParamTys);
+}
+
+unsigned TargetTransformInfo::getIntrinsicCost(
+    Intrinsic::ID IID, Type *RetTy, ArrayRef<const Value *> Arguments) const {
+  return PrevTTI->getIntrinsicCost(IID, RetTy, Arguments);
+}
+
 unsigned TargetTransformInfo::getUserCost(const User *U) const {
   return PrevTTI->getUserCost(U);
 }
 
+bool TargetTransformInfo::isLoweredToCall(const Function *F) const {
+  return PrevTTI->isLoweredToCall(F);
+}
+
 bool TargetTransformInfo::isLegalAddImmediate(int64_t Imm) const {
   return PrevTTI->isLegalAddImmediate(Imm);
 }
@@ -179,6 +209,7 @@ struct NoTTI : ImmutablePass, TargetTransformInfo {
   virtual void initializePass() {
     // Note that this subclass is special, and must *not* call initializeTTI as
     // it does not chain.
+    TopTTI = this;
     PrevTTI = 0;
     DL = getAnalysisIfAvailable<DataLayout>();
   }
@@ -257,6 +288,84 @@ struct NoTTI : ImmutablePass, TargetTransformInfo {
     return TCC_Free;
   }
 
+  unsigned getCallCost(FunctionType *FTy, int NumArgs = -1) const {
+    assert(FTy && "FunctionType must be provided to this routine.");
+
+    // The target-independent implementation just measures the size of the
+    // function by approximating that each argument will take on average one
+    // instruction to prepare.
+
+    if (NumArgs < 0)
+      // Set the argument number to the number of explicit arguments in the
+      // function.
+      NumArgs = FTy->getNumParams();
+
+    return TCC_Basic * (NumArgs + 1);
+  }
+
+  unsigned getCallCost(const Function *F, int NumArgs = -1) const {
+    assert(F && "A concrete function must be provided to this routine.");
+
+    if (NumArgs < 0)
+      // Set the argument number to the number of explicit arguments in the
+      // function.
+      NumArgs = F->arg_size();
+
+    if (Intrinsic::ID IID = (Intrinsic::ID)F->getIntrinsicID()) {
+      FunctionType *FTy = F->getFunctionType();
+      SmallVector<Type *, 8> ParamTys(FTy->param_begin(), FTy->param_end());
+      return TopTTI->getIntrinsicCost(IID, FTy->getReturnType(), ParamTys);
+    }
+
+    if (!TopTTI->isLoweredToCall(F))
+      return TCC_Basic; // Give a basic cost if it will be lowered directly.
+
+    return TopTTI->getCallCost(F->getFunctionType(), NumArgs);
+  }
+
+  unsigned getCallCost(const Function *F,
+                       ArrayRef<const Value *> Arguments) const {
+    // Simply delegate to generic handling of the call.
+    // FIXME: We should use instsimplify or something else to catch calls which
+    // will constant fold with these arguments.
+    return TopTTI->getCallCost(F, Arguments.size());
+  }
+
+  unsigned getIntrinsicCost(Intrinsic::ID IID, Type *RetTy,
+                            ArrayRef<Type *> ParamTys) const {
+    switch (IID) {
+    default:
+      // Intrinsics rarely (if ever) have normal argument setup constraints.
+      // Model them as having a basic instruction cost.
+      // FIXME: This is wrong for libc intrinsics.
+      return TCC_Basic;
+
+    case Intrinsic::dbg_declare:
+    case Intrinsic::dbg_value:
+    case Intrinsic::invariant_start:
+    case Intrinsic::invariant_end:
+    case Intrinsic::lifetime_start:
+    case Intrinsic::lifetime_end:
+    case Intrinsic::objectsize:
+    case Intrinsic::ptr_annotation:
+    case Intrinsic::var_annotation:
+      // These intrinsics don't actually represent code after lowering.
+      return TCC_Free;
+    }
+  }
+
+  unsigned getIntrinsicCost(Intrinsic::ID IID, Type *RetTy,
+                            ArrayRef<const Value *> Arguments) const {
+    // Delegate to the generic intrinsic handling code. This mostly provides an
+    // opportunity for targets to (for example) special case the cost of
+    // certain intrinsics based on constants used as arguments.
+    SmallVector<Type *, 8> ParamTys;
+    ParamTys.reserve(Arguments.size());
+    for (unsigned Idx = 0, Size = Arguments.size(); Idx != Size; ++Idx)
+      ParamTys.push_back(Arguments[Idx]->getType());
+    return TopTTI->getIntrinsicCost(IID, RetTy, ParamTys);
+  }
+
   unsigned getUserCost(const User *U) const {
     if (isa<PHINode>(U))
       return TCC_Free; // Model all PHI nodes as free.
@@ -266,25 +375,21 @@ struct NoTTI : ImmutablePass, TargetTransformInfo {
       // folded into their uses via addressing modes.
       return GEP->hasAllConstantIndices() ? TCC_Free : TCC_Basic;
 
-    // If we have a call of an intrinsic we can provide more detailed analysis
-    // by inspecting the particular intrinsic called.
-    // FIXME: Hoist this out into a getIntrinsicCost routine.
-    if (const IntrinsicInst *II = dyn_cast<IntrinsicInst>(U)) {
-      switch (II->getIntrinsicID()) {
-      default:
-        return TCC_Basic;
-      case Intrinsic::dbg_declare:
-      case Intrinsic::dbg_value:
-      case Intrinsic::invariant_start:
-      case Intrinsic::invariant_end:
-      case Intrinsic::lifetime_start:
-      case Intrinsic::lifetime_end:
-      case Intrinsic::objectsize:
-      case Intrinsic::ptr_annotation:
-      case Intrinsic::var_annotation:
-        // These intrinsics don't count as size.
-        return TCC_Free;
+    if (ImmutableCallSite CS = U) {
+      const Function *F = CS.getCalledFunction();
+      if (!F) {
+        // Just use the called value type.
+        Type *FTy = CS.getCalledValue()->getType()->getPointerElementType();
+        return TopTTI->getCallCost(cast<FunctionType>(FTy), CS.arg_size());
       }
+
+      SmallVector<const Value *, 8> Arguments;
+      for (ImmutableCallSite::arg_iterator AI = CS.arg_begin(),
+                                           AE = CS.arg_end();
+           AI != AE; ++AI)
+        Arguments.push_back(*AI);
+
+      return TopTTI->getCallCost(F, Arguments);
     }
 
     if (const CastInst *CI = dyn_cast<CastInst>(U)) {
@@ -301,6 +406,37 @@ struct NoTTI : ImmutablePass, TargetTransformInfo {
                                 U->getOperand(0)->getType() : 0);
   }
 
+  bool isLoweredToCall(const Function *F) const {
+    // FIXME: These should almost certainly not be handled here, and instead
+    // handled with the help of TLI or the target itself. This was largely
+    // ported from existing analysis heuristics here so that such refactorings
+    // can take place in the future.
+
+    if (F->isIntrinsic())
+      return false;
+
+    if (F->hasLocalLinkage() || !F->hasName())
+      return true;
+
+    StringRef Name = F->getName();
+
+    // These will all likely lower to a single selection DAG node.
+    if (Name == "copysign" || Name == "copysignf" || Name == "copysignl" ||
+        Name == "fabs" || Name == "fabsf" || Name == "fabsl" || Name == "sin" ||
+        Name == "sinf" || Name == "sinl" || Name == "cos" || Name == "cosf" ||
+        Name == "cosl" || Name == "sqrt" || Name == "sqrtf" || Name == "sqrtl")
+      return false;
+
+    // These are all likely to be optimized into something smaller.
+    if (Name == "pow" || Name == "powf" || Name == "powl" || Name == "exp2" ||
+        Name == "exp2l" || Name == "exp2f" || Name == "floor" || Name ==
+        "floorf" || Name == "ceil" || Name == "round" || Name == "ffs" ||
+        Name == "ffsl" || Name == "abs" || Name == "labs" || Name == "llabs")
+      return false;
+
+    return true;
+  }
+
   bool isLegalAddImmediate(int64_t Imm) const {
     return false;
   }