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.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@173148 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 49 insertions, 0 deletions

diff --git a/include/llvm/Analysis/TargetTransformInfo.h b/include/llvm/Analysis/TargetTransformInfo.h
index 876082f890..681b838bc7 100644
--- a/include/llvm/Analysis/TargetTransformInfo.h
+++ b/include/llvm/Analysis/TargetTransformInfo.h
@@ -117,6 +117,41 @@ public:
   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 @@ public:
   /// 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