[llvm] [Passes] Run LoopSimplify before SLP (PR #209332)

[Hari Limaye via llvm-commits]

https://github.com/hazzlim created https://github.com/llvm/llvm-project/pull/209332

Run LoopSimplify before SLP in the default pipeline, to ensure that SLP sees loops in Loop Simplify Form and to improve and simplify SLP loop-aware cost modelling.

>From e9313d20b133e765860e60a356b87ca01470f4a9 Mon Sep 17 00:00:00 2001
From: Hari Limaye <hari.limaye at arm.com>
Date: Sun, 12 Jul 2026 18:56:07 +0000
Subject: [PATCH] [Passes] Run LoopSimplify before SLP

---
 llvm/lib/Passes/PassBuilderPipelines.cpp                      | 2 ++
 llvm/test/Other/new-pm-defaults.ll                            | 1 +
 llvm/test/Other/new-pm-lto-defaults.ll                        | 1 +
 llvm/test/Other/new-pm-thinlto-postlink-defaults.ll           | 1 +
 llvm/test/Other/new-pm-thinlto-postlink-pgo-defaults.ll       | 1 +
 llvm/test/Other/new-pm-thinlto-postlink-samplepgo-defaults.ll | 1 +
 6 files changed, 7 insertions(+)

diff --git a/llvm/lib/Passes/PassBuilderPipelines.cpp b/llvm/lib/Passes/PassBuilderPipelines.cpp
index f89dc099a9128..3ec1d6db51790 100644
--- a/llvm/lib/Passes/PassBuilderPipelines.cpp
+++ b/llvm/lib/Passes/PassBuilderPipelines.cpp
@@ -1449,6 +1449,8 @@ void PassBuilder::addVectorPasses(OptimizationLevel Level,
 
   // Optimize parallel scalar instruction chains into SIMD instructions.
   if (PTO.SLPVectorization) {
+    // Canonicalize loops before SLP so loop-aware modeling observes loop-simplify form.
+    FPM.addPass(LoopSimplifyPass());
     FPM.addPass(SLPVectorizerPass());
     if (Level.getSpeedupLevel() > 1 && ExtraVectorizerPasses) {
       FPM.addPass(EarlyCSEPass());
diff --git a/llvm/test/Other/new-pm-defaults.ll b/llvm/test/Other/new-pm-defaults.ll
index c3a8ab3725ad6..18cf91392e6da 100644
--- a/llvm/test/Other/new-pm-defaults.ll
+++ b/llvm/test/Other/new-pm-defaults.ll
@@ -253,6 +253,7 @@
 ; CHECK-O-NEXT: Running pass: LoopLoadEliminationPass
 ; CHECK-O-NEXT: Running pass: InstCombinePass
 ; CHECK-O-NEXT: Running pass: SimplifyCFGPass
+; CHECK-O23-NEXT: Running pass: LoopSimplifyPass
 ; CHECK-O23-NEXT: Running pass: SLPVectorizerPass
 ; CHECK-O-NEXT: Running pass: VectorCombinePass
 ; CHECK-O-NEXT: Running pass: InstCombinePass
diff --git a/llvm/test/Other/new-pm-lto-defaults.ll b/llvm/test/Other/new-pm-lto-defaults.ll
index 14f189194d0e3..24be69d74748c 100644
--- a/llvm/test/Other/new-pm-lto-defaults.ll
+++ b/llvm/test/Other/new-pm-lto-defaults.ll
@@ -138,6 +138,7 @@
 ; CHECK-O23-NEXT: Running pass: SCCPPass on foo
 ; CHECK-O23-NEXT: Running pass: InstCombinePass on foo
 ; CHECK-O23-NEXT: Running pass: BDCEPass on foo
+; CHECK-O23-NEXT: Running pass: LoopSimplifyPass on foo
 ; CHECK-O23-NEXT: Running pass: SLPVectorizerPass on foo
 ; CHECK-O23-NEXT: Running pass: VectorCombinePass on foo
 ; CHECK-O23-NEXT: Running pass: InferAlignmentPass on foo
diff --git a/llvm/test/Other/new-pm-thinlto-postlink-defaults.ll b/llvm/test/Other/new-pm-thinlto-postlink-defaults.ll
index df712ab7846f8..f4e793a4f83d9 100644
--- a/llvm/test/Other/new-pm-thinlto-postlink-defaults.ll
+++ b/llvm/test/Other/new-pm-thinlto-postlink-defaults.ll
@@ -180,6 +180,7 @@
 ; CHECK-POSTLINK-O-NEXT: Running pass: LoopLoadEliminationPass
 ; CHECK-POSTLINK-O-NEXT: Running pass: InstCombinePass
 ; CHECK-POSTLINK-O-NEXT: Running pass: SimplifyCFGPass
+; CHECK-O23-NEXT: Running pass: LoopSimplifyPass
 ; CHECK-O23-NEXT: Running pass: SLPVectorizerPass
 ; CHECK-POSTLINK-O-NEXT: Running pass: VectorCombinePass
 ; CHECK-POSTLINK-O-NEXT: Running pass: InstCombinePass
diff --git a/llvm/test/Other/new-pm-thinlto-postlink-pgo-defaults.ll b/llvm/test/Other/new-pm-thinlto-postlink-pgo-defaults.ll
index f098951e1403d..ac84645b2dd68 100644
--- a/llvm/test/Other/new-pm-thinlto-postlink-pgo-defaults.ll
+++ b/llvm/test/Other/new-pm-thinlto-postlink-pgo-defaults.ll
@@ -165,6 +165,7 @@
 ; CHECK-O-NEXT: Running pass: LoopLoadEliminationPass
 ; CHECK-O-NEXT: Running pass: InstCombinePass
 ; CHECK-O-NEXT: Running pass: SimplifyCFGPass
+; CHECK-O23-NEXT: Running pass: LoopSimplifyPass
 ; CHECK-O23-NEXT: Running pass: SLPVectorizerPass
 ; CHECK-O-NEXT: Running pass: VectorCombinePass
 ; CHECK-O-NEXT: Running pass: InstCombinePass
diff --git a/llvm/test/Other/new-pm-thinlto-postlink-samplepgo-defaults.ll b/llvm/test/Other/new-pm-thinlto-postlink-samplepgo-defaults.ll
index 702920e5a6dbf..19a91319612c3 100644
--- a/llvm/test/Other/new-pm-thinlto-postlink-samplepgo-defaults.ll
+++ b/llvm/test/Other/new-pm-thinlto-postlink-samplepgo-defaults.ll
@@ -172,6 +172,7 @@
 ; CHECK-O-NEXT: Running pass: LoopLoadEliminationPass
 ; CHECK-O-NEXT: Running pass: InstCombinePass
 ; CHECK-O-NEXT: Running pass: SimplifyCFGPass
+; CHECK-O23-NEXT: Running pass: LoopSimplifyPass
 ; CHECK-O23-NEXT: Running pass: SLPVectorizerPass
 ; CHECK-O-NEXT: Running pass: VectorCombinePass
 ; CHECK-O-NEXT: Running pass: InstCombinePass