[llvm] [LoopFlatten] Enable by default (PR #214175)

Kamlesh Kumar via llvm-commits llvm-commits at lists.llvm.org
Wed Aug 5 02:55:29 PDT 2026 

https://github.com/kamleshbhalui created https://github.com/llvm/llvm-project/pull/214175

I did not find any correctness issues across llvm testsuite and spec cpu v6/8.

>From ce62e4a5528daaa96082109014e98e4f43252312 Mon Sep 17 00:00:00 2001
From: Kamlesh Kumar <kamlesh.kumar at arm.com>
Date: Wed, 5 Aug 2026 09:50:19 +0000
Subject: [PATCH] [LoopFlatten] Enable by default

---
 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 +
 llvm/test/Other/new-pm-thinlto-prelink-defaults.ll            | 1 +
 llvm/test/Other/new-pm-thinlto-prelink-pgo-defaults.ll        | 1 +
 llvm/test/Other/new-pm-thinlto-prelink-samplepgo-defaults.ll  | 1 +
 9 files changed, 9 insertions(+), 1 deletion(-)

diff --git a/llvm/lib/Passes/PassBuilderPipelines.cpp b/llvm/lib/Passes/PassBuilderPipelines.cpp
index b8c5b1eab2f97..50482673515e2 100644
--- a/llvm/lib/Passes/PassBuilderPipelines.cpp
+++ b/llvm/lib/Passes/PassBuilderPipelines.cpp
@@ -225,7 +225,7 @@ static cl::opt<bool> EnableUnrollAndJam("enable-unroll-and-jam",
                                         cl::init(false), cl::Hidden,
                                         cl::desc("Enable Unroll And Jam Pass"));
 
-static cl::opt<bool> EnableLoopFlatten("enable-loop-flatten", cl::init(false),
+static cl::opt<bool> EnableLoopFlatten("enable-loop-flatten", cl::init(true),
                                        cl::Hidden,
                                        cl::desc("Enable the LoopFlatten Pass"));
 
diff --git a/llvm/test/Other/new-pm-defaults.ll b/llvm/test/Other/new-pm-defaults.ll
index 6b2edf339dfdf..e225afd31ef9c 100644
--- a/llvm/test/Other/new-pm-defaults.ll
+++ b/llvm/test/Other/new-pm-defaults.ll
@@ -168,6 +168,7 @@
 ; CHECK-O-NEXT: Running pass: LoopRotatePass
 ; CHECK-O-NEXT: Running pass: LICM
 ; CHECK-O-NEXT: Running pass: SimpleLoopUnswitchPass
+; CHECK-O-NEXT: Running pass: LoopFlattenPass
 ; CHECK-O-NEXT: Running pass: SimplifyCFGPass
 ; CHECK-O-NEXT: Running pass: InstCombinePass
 ; CHECK-O-NEXT: Running pass: LoopSimplifyPass
diff --git a/llvm/test/Other/new-pm-lto-defaults.ll b/llvm/test/Other/new-pm-lto-defaults.ll
index 14f189194d0e3..40c8c1837bdc1 100644
--- a/llvm/test/Other/new-pm-lto-defaults.ll
+++ b/llvm/test/Other/new-pm-lto-defaults.ll
@@ -121,6 +121,7 @@
 ; CHECK-EP-VECTORIZER-START-NEXT: Running pass: NoOpFunctionPass on foo
 ; CHECK-O23-NEXT: Running pass: LoopSimplifyPass on foo
 ; CHECK-O23-NEXT: Running pass: LCSSAPass on foo
+; CHECK-O23-NEXT: Running pass: LoopFlattenPass on loop
 ; CHECK-O23-NEXT: Running pass: IndVarSimplifyPass on loop
 ; CHECK-O23-NEXT: Running pass: LoopDeletionPass on loop
 ; CHECK-O23-NEXT: Running pass: LoopFullUnrollPass on loop
diff --git a/llvm/test/Other/new-pm-thinlto-postlink-defaults.ll b/llvm/test/Other/new-pm-thinlto-postlink-defaults.ll
index 0361db887cb61..c6b5d58f92460 100644
--- a/llvm/test/Other/new-pm-thinlto-postlink-defaults.ll
+++ b/llvm/test/Other/new-pm-thinlto-postlink-defaults.ll
@@ -108,6 +108,7 @@
 ; CHECK-O-NEXT: Running pass: LoopRotatePass
 ; CHECK-O-NEXT: Running pass: LICM
 ; CHECK-O-NEXT: Running pass: SimpleLoopUnswitchPass
+; CHECK-O-NEXT: Running pass: LoopFlattenPass
 ; CHECK-O-NEXT: Running pass: SimplifyCFGPass
 ; CHECK-O-NEXT: Running pass: InstCombinePass
 ; CHECK-O-NEXT: Running pass: LoopSimplifyPass
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 6f7be4049f434..dda4f051923f9 100644
--- a/llvm/test/Other/new-pm-thinlto-postlink-pgo-defaults.ll
+++ b/llvm/test/Other/new-pm-thinlto-postlink-pgo-defaults.ll
@@ -95,6 +95,7 @@
 ; CHECK-O-NEXT: Running pass: LoopRotatePass
 ; CHECK-O-NEXT: Running pass: LICM
 ; CHECK-O-NEXT: Running pass: SimpleLoopUnswitchPass
+; CHECK-O-NEXT: Running pass: LoopFlattenPass
 ; CHECK-O-NEXT: Running pass: SimplifyCFGPass
 ; CHECK-O-NEXT: Running pass: InstCombinePass
 ; CHECK-O-NEXT: Running pass: LoopSimplifyPass
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 c8ba790045f80..33fa2afd3aa08 100644
--- a/llvm/test/Other/new-pm-thinlto-postlink-samplepgo-defaults.ll
+++ b/llvm/test/Other/new-pm-thinlto-postlink-samplepgo-defaults.ll
@@ -102,6 +102,7 @@
 ; CHECK-O-NEXT: Running pass: LoopRotatePass
 ; CHECK-O-NEXT: Running pass: LICM
 ; CHECK-O-NEXT: Running pass: SimpleLoopUnswitchPass
+; CHECK-O-NEXT: Running pass: LoopFlattenPass
 ; CHECK-O-NEXT: Running pass: SimplifyCFGPass
 ; CHECK-O-NEXT: Running pass: InstCombinePass
 ; CHECK-O-NEXT: Running pass: LoopSimplifyPass
diff --git a/llvm/test/Other/new-pm-thinlto-prelink-defaults.ll b/llvm/test/Other/new-pm-thinlto-prelink-defaults.ll
index 30f49dffaeeac..7ee316429acf5 100644
--- a/llvm/test/Other/new-pm-thinlto-prelink-defaults.ll
+++ b/llvm/test/Other/new-pm-thinlto-prelink-defaults.ll
@@ -134,6 +134,7 @@
 ; CHECK-O-NEXT: Running pass: LoopRotatePass
 ; CHECK-O-NEXT: Running pass: LICM
 ; CHECK-O-NEXT: Running pass: SimpleLoopUnswitchPass
+; CHECK-O-NEXT: Running pass: LoopFlattenPass
 ; CHECK-O-NEXT: Running pass: SimplifyCFGPass
 ; CHECK-O-NEXT: Running pass: InstCombinePass
 ; CHECK-O-NEXT: Running pass: LoopSimplifyPass
diff --git a/llvm/test/Other/new-pm-thinlto-prelink-pgo-defaults.ll b/llvm/test/Other/new-pm-thinlto-prelink-pgo-defaults.ll
index 54adc37e41079..7dccc623693f6 100644
--- a/llvm/test/Other/new-pm-thinlto-prelink-pgo-defaults.ll
+++ b/llvm/test/Other/new-pm-thinlto-prelink-pgo-defaults.ll
@@ -142,6 +142,7 @@
 ; CHECK-O-NEXT: Running pass: LoopRotatePass
 ; CHECK-O-NEXT: Running pass: LICM
 ; CHECK-O-NEXT: Running pass: SimpleLoopUnswitchPass
+; CHECK-O-NEXT: Running pass: LoopFlattenPass
 ; CHECK-O-NEXT: Running pass: SimplifyCFGPass
 ; CHECK-O-NEXT: Running pass: InstCombinePass
 ; CHECK-O-NEXT: Running pass: LoopSimplifyPass
diff --git a/llvm/test/Other/new-pm-thinlto-prelink-samplepgo-defaults.ll b/llvm/test/Other/new-pm-thinlto-prelink-samplepgo-defaults.ll
index 9540093a4bf22..43ddc732a8878 100644
--- a/llvm/test/Other/new-pm-thinlto-prelink-samplepgo-defaults.ll
+++ b/llvm/test/Other/new-pm-thinlto-prelink-samplepgo-defaults.ll
@@ -107,6 +107,7 @@
 ; CHECK-O-NEXT: Running pass: LoopRotatePass
 ; CHECK-O-NEXT: Running pass: LICM
 ; CHECK-O-NEXT: Running pass: SimpleLoopUnswitchPass
+; CHECK-O-NEXT: Running pass: LoopFlattenPass
 ; CHECK-O-NEXT: Running pass: SimplifyCFGPass
 ; CHECK-O-NEXT: Running pass: InstCombinePass
 ; CHECK-O-NEXT: Running pass: LoopSimplifyPass

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