[llvm-branch-commits] [llvm] [LV] Disable VPlan-based cost model for 19.x release. (PR #100097)

[Florian Hahn via llvm-branch-commits]

https://github.com/fhahn created https://github.com/llvm/llvm-project/pull/100097

As discussed in  https://github.com/llvm/llvm-project/pull/92555 flip the default for the option added in
https://github.com/llvm/llvm-project/pull/99536 to true.

This restores the original behavior for the release branch to give the VPlan-based cost model more time to mature on main.

>From a72a0bf44a8b259be3c62e79082d2fdc04fc2771 Mon Sep 17 00:00:00 2001
From: Florian Hahn <flo at fhahn.com>
Date: Tue, 23 Jul 2024 11:15:26 +0100
Subject: [PATCH] [LV] Disable VPlan-based cost model for 19.x release.

As discussed in  https://github.com/llvm/llvm-project/pull/92555 flip
the default for the option added in
https://github.com/llvm/llvm-project/pull/99536 to true.

This restores the original behavior for the release branch to give the
VPlan-based cost model more time to mature on main.
---
 llvm/lib/Transforms/Vectorize/LoopVectorize.cpp                 | 2 +-
 .../test/Transforms/LoopVectorize/RISCV/riscv-vector-reverse.ll | 2 --
 2 files changed, 1 insertion(+), 3 deletions(-)

diff --git a/llvm/lib/Transforms/Vectorize/LoopVectorize.cpp b/llvm/lib/Transforms/Vectorize/LoopVectorize.cpp
index 6d28b8fabe42e..68363abdb817a 100644
--- a/llvm/lib/Transforms/Vectorize/LoopVectorize.cpp
+++ b/llvm/lib/Transforms/Vectorize/LoopVectorize.cpp
@@ -206,7 +206,7 @@ static cl::opt<unsigned> VectorizeMemoryCheckThreshold(
     cl::desc("The maximum allowed number of runtime memory checks"));
 
 static cl::opt<bool> UseLegacyCostModel(
-    "vectorize-use-legacy-cost-model", cl::init(false), cl::Hidden,
+    "vectorize-use-legacy-cost-model", cl::init(true), cl::Hidden,
     cl::desc("Use the legacy cost model instead of the VPlan-based cost model. "
              "This option will be removed in the future."));
 
diff --git a/llvm/test/Transforms/LoopVectorize/RISCV/riscv-vector-reverse.ll b/llvm/test/Transforms/LoopVectorize/RISCV/riscv-vector-reverse.ll
index fc310f4163082..1a78eaf644723 100644
--- a/llvm/test/Transforms/LoopVectorize/RISCV/riscv-vector-reverse.ll
+++ b/llvm/test/Transforms/LoopVectorize/RISCV/riscv-vector-reverse.ll
@@ -135,7 +135,6 @@ define void @vector_reverse_i64(ptr nocapture noundef writeonly %A, ptr nocaptur
 ; CHECK-NEXT:  LV: Interleaving is not beneficial.
 ; CHECK-NEXT:  LV: Found a vectorizable loop (vscale x 4) in <stdin>
 ; CHECK-NEXT:  LEV: Epilogue vectorization is not profitable for this loop
-; CHECK-NEXT:  VF picked by VPlan cost model: vscale x 4
 ; CHECK-NEXT:  Executing best plan with VF=vscale x 4, UF=1
 ; CHECK-NEXT:  VPlan 'Final VPlan for VF={vscale x 4},UF>=1' {
 ; CHECK-NEXT:  Live-in vp<%0> = VF * UF
@@ -339,7 +338,6 @@ define void @vector_reverse_f32(ptr nocapture noundef writeonly %A, ptr nocaptur
 ; CHECK-NEXT:  LV: Interleaving is not beneficial.
 ; CHECK-NEXT:  LV: Found a vectorizable loop (vscale x 4) in <stdin>
 ; CHECK-NEXT:  LEV: Epilogue vectorization is not profitable for this loop
-; CHECK-NEXT:  VF picked by VPlan cost model: vscale x 4
 ; CHECK-NEXT:  Executing best plan with VF=vscale x 4, UF=1
 ; CHECK-NEXT:  VPlan 'Final VPlan for VF={vscale x 4},UF>=1' {
 ; CHECK-NEXT:  Live-in vp<%0> = VF * UF