diff options
| -rw-r--r-- | llvm/include/llvm/Analysis/TargetTransformInfo.h | 18 |
1 files changed, 14 insertions, 4 deletions
diff --git a/llvm/include/llvm/Analysis/TargetTransformInfo.h b/llvm/include/llvm/Analysis/TargetTransformInfo.h index b1abc792333..22d7149d35e 100644 --- a/llvm/include/llvm/Analysis/TargetTransformInfo.h +++ b/llvm/include/llvm/Analysis/TargetTransformInfo.h @@ -710,10 +710,20 @@ public: /// and the number of execution units in the CPU. unsigned getMaxInterleaveFactor(unsigned VF) const; - /// \return The expected cost of arithmetic ops, such as mul, xor, fsub, etc. - /// \p Args is an optional argument which holds the instruction operands - /// values so the TTI can analyize those values searching for special - /// cases\optimizations based on those values. + /// This is an approximation of reciprocal throughput of a math/logic op. + /// A higher cost indicates less expected throughput. + /// From Agner Fog's guides, reciprocal throughput is "the average number of + /// clock cycles per instruction when the instructions are not part of a + /// limiting dependency chain." + /// Therefore, costs should be scaled to account for multiple execution units + /// on the target that can process this type of instruction. For example, if + /// there are 5 scalar integer units and 2 vector integer units that can + /// calculate an 'add' in a single cycle, this model should indicate that the + /// cost of the vector add instruction is 2.5 times the cost of the scalar + /// add instruction. + /// \p Args is an optional argument which holds the instruction operands + /// values so the TTI can analyze those values searching for special + /// cases or optimizations based on those values. int getArithmeticInstrCost( unsigned Opcode, Type *Ty, OperandValueKind Opd1Info = OK_AnyValue, OperandValueKind Opd2Info = OK_AnyValue, |
