[llvm] [LV] Prevent query the computeCost() when VF=1 in emitInvalidCostRemarks(). (PR #117288)

[Elvis Wang via llvm-commits]

https://github.com/ElvisWang123 updated https://github.com/llvm/llvm-project/pull/117288

>From 2e9579df67c5ab62a7133649dc329f8abe5a669c Mon Sep 17 00:00:00 2001
From: Elvis Wang <elvis.wang at sifive.com>
Date: Thu, 21 Nov 2024 21:02:55 -0800
Subject: [PATCH 1/2] [LV] Prevent query the computeCost() when VF=1 in
 emitInvalidCostRemarks().

---
 llvm/lib/Transforms/Vectorize/LoopVectorize.cpp | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/llvm/lib/Transforms/Vectorize/LoopVectorize.cpp b/llvm/lib/Transforms/Vectorize/LoopVectorize.cpp
index 90312c1a28df3c..6db52aad9625f9 100644
--- a/llvm/lib/Transforms/Vectorize/LoopVectorize.cpp
+++ b/llvm/lib/Transforms/Vectorize/LoopVectorize.cpp
@@ -4372,6 +4372,9 @@ void LoopVectorizationPlanner::emitInvalidCostRemarks(
   SmallVector<RecipeVFPair> InvalidCosts;
   for (const auto &Plan : VPlans) {
     for (ElementCount VF : Plan->vectorFactors()) {
+      if (VF.isScalar())
+        continue;
+
       VPCostContext CostCtx(CM.TTI, *CM.TLI, Legal->getWidestInductionType(),
                             CM);
       precomputeCosts(*Plan, VF, CostCtx);

>From f30cdb01be0fda35224afe6562699c7a9eb9ecad Mon Sep 17 00:00:00 2001
From: Elvis Wang <elvis.wang at sifive.com>
Date: Thu, 12 Dec 2024 15:33:02 -0800
Subject: [PATCH 2/2] Add comments to explain why we skip scalar cost.

---
 llvm/lib/Transforms/Vectorize/LoopVectorize.cpp | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/llvm/lib/Transforms/Vectorize/LoopVectorize.cpp b/llvm/lib/Transforms/Vectorize/LoopVectorize.cpp
index 6db52aad9625f9..cc30d94f7c5037 100644
--- a/llvm/lib/Transforms/Vectorize/LoopVectorize.cpp
+++ b/llvm/lib/Transforms/Vectorize/LoopVectorize.cpp
@@ -4372,6 +4372,9 @@ void LoopVectorizationPlanner::emitInvalidCostRemarks(
   SmallVector<RecipeVFPair> InvalidCosts;
   for (const auto &Plan : VPlans) {
     for (ElementCount VF : Plan->vectorFactors()) {
+      // The VPlan-based cost model is designed for computing vector cost.
+      // Quering VPlan-based cost model with scarlar VF will cause some error
+      // because we expect the VF is vector for most of the widen recipes.
       if (VF.isScalar())
         continue;