[llvm] [RISCV][NFC] Clarify getRISCVInstructionCost usage (PR #121556)

[Shih-Po Hung via llvm-commits]

https://github.com/arcbbb updated https://github.com/llvm/llvm-project/pull/121556

>From 9402fbb4460206d6b3e75e58d425aedc49f1f0c3 Mon Sep 17 00:00:00 2001
From: ShihPo Hung <shihpo.hung at sifive.com>
Date: Fri, 3 Jan 2025 01:20:43 -0800
Subject: [PATCH 1/2] [RISCV][TTI] Use vtype for getRISCVInstructionCost

---
 llvm/lib/Target/RISCV/RISCVTargetTransformInfo.h | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/llvm/lib/Target/RISCV/RISCVTargetTransformInfo.h b/llvm/lib/Target/RISCV/RISCVTargetTransformInfo.h
index 9b364391f0fa47..3a9073731681ef 100644
--- a/llvm/lib/Target/RISCV/RISCVTargetTransformInfo.h
+++ b/llvm/lib/Target/RISCV/RISCVTargetTransformInfo.h
@@ -48,6 +48,11 @@ class RISCVTTIImpl : public BasicTTIImplBase<RISCVTTIImpl> {
   /// actual target hardware.
   unsigned getEstimatedVLFor(VectorType *Ty);
 
+  /// This function calculates the costs for one or more RVV opcodes based
+  /// on the vtype and the cost kind.
+  /// \param Opcodes A list of opcodes of the RVV instruction to evaluate.
+  /// \param VT The MVT of vtype associated with the RVV instructions.
+  /// \param CostKind The type of cost to compute.
   InstructionCost getRISCVInstructionCost(ArrayRef<unsigned> OpCodes, MVT VT,
                                           TTI::TargetCostKind CostKind);
 

>From 02f633cc4323988f4f7e88d88073b29f4435f63c Mon Sep 17 00:00:00 2001
From: ShihPo Hung <shihpo.hung at sifive.com>
Date: Sun, 2 Feb 2025 23:36:36 -0800
Subject: [PATCH 2/2] Add comments for widening/narrowing instructions

---
 llvm/lib/Target/RISCV/RISCVTargetTransformInfo.h | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/llvm/lib/Target/RISCV/RISCVTargetTransformInfo.h b/llvm/lib/Target/RISCV/RISCVTargetTransformInfo.h
index 3a9073731681ef..042530b9cd2b32 100644
--- a/llvm/lib/Target/RISCV/RISCVTargetTransformInfo.h
+++ b/llvm/lib/Target/RISCV/RISCVTargetTransformInfo.h
@@ -52,6 +52,9 @@ class RISCVTTIImpl : public BasicTTIImplBase<RISCVTTIImpl> {
   /// on the vtype and the cost kind.
   /// \param Opcodes A list of opcodes of the RVV instruction to evaluate.
   /// \param VT The MVT of vtype associated with the RVV instructions.
+  /// For widening/narrowing instructions where the result and source types
+  /// differ, it is important to check the spec to determine whether the vtype
+  /// refers to the result or source type.
   /// \param CostKind The type of cost to compute.
   InstructionCost getRISCVInstructionCost(ArrayRef<unsigned> OpCodes, MVT VT,
                                           TTI::TargetCostKind CostKind);