[llvm] [LTO] Run Argument Promotion before IPSCCP (PR #111163)

[Hari Limaye via llvm-commits]

https://github.com/hazzlim updated https://github.com/llvm/llvm-project/pull/111163

>From cc21d1909aa06c9f84233d9fecfad81ddfed1e3b Mon Sep 17 00:00:00 2001
From: Hari Limaye <hari.limaye at arm.com>
Date: Tue, 24 Sep 2024 16:12:29 +0000
Subject: [PATCH] [LTO] Run Argument Promotion before IPSCCP

Run ArgumentPromotion before IPSCCP in the LTO pipeline, to expose more
constants to be propagated. We also run PostOrderFunctionAttrs to
improve the information available to ArgumentPromotion's alias analysis,
and SROA to clean up allocas.
---
 llvm/lib/Passes/PassBuilderPipelines.cpp | 9 +++++++++
 llvm/test/Other/new-pm-lto-defaults.ll   | 9 ++++++---
 2 files changed, 15 insertions(+), 3 deletions(-)

diff --git a/llvm/lib/Passes/PassBuilderPipelines.cpp b/llvm/lib/Passes/PassBuilderPipelines.cpp
index 8f151a99b11709..cdb9431c755bce 100644
--- a/llvm/lib/Passes/PassBuilderPipelines.cpp
+++ b/llvm/lib/Passes/PassBuilderPipelines.cpp
@@ -1831,6 +1831,15 @@ PassBuilder::buildLTODefaultPipeline(OptimizationLevel Level,
     MPM.addPass(PGOIndirectCallPromotion(
         true /* InLTO */, PGOOpt && PGOOpt->Action == PGOOptions::SampleUse));
 
+    // Promoting by-reference arguments to by-value exposes more constants to
+    // IPSCCP.
+    MPM.addPass(createModuleToPostOrderCGSCCPassAdaptor(
+        PostOrderFunctionAttrsPass(/*SkipNonRecursive*/ true)));
+    MPM.addPass(
+        createModuleToPostOrderCGSCCPassAdaptor(ArgumentPromotionPass()));
+    MPM.addPass(
+        createModuleToFunctionPassAdaptor(SROAPass(SROAOptions::ModifyCFG)));
+
     // Propagate constants at call sites into the functions they call.  This
     // opens opportunities for globalopt (and inlining) by substituting function
     // pointers passed as arguments to direct uses of functions.
diff --git a/llvm/test/Other/new-pm-lto-defaults.ll b/llvm/test/Other/new-pm-lto-defaults.ll
index 5543472df685b0..2dd754ecef4d7b 100644
--- a/llvm/test/Other/new-pm-lto-defaults.ll
+++ b/llvm/test/Other/new-pm-lto-defaults.ll
@@ -41,14 +41,17 @@
 ; CHECK-O23SZ-NEXT: PGOIndirectCallPromotion
 ; CHECK-O23SZ-NEXT: Running analysis: ProfileSummaryAnalysis
 ; CHECK-O23SZ-NEXT: Running analysis: OptimizationRemarkEmitterAnalysis
-; CHECK-O23SZ-NEXT: Running pass: IPSCCPPass
-; CHECK-O23SZ-NEXT: Running analysis: AssumptionAnalysis on foo
-; CHECK-O23SZ-NEXT: Running pass: CalledValuePropagationPass
 ; CHECK-O-NEXT: Running analysis: InnerAnalysisManagerProxy<{{.*}}SCC
 ; CHECK-O-NEXT: Running analysis: LazyCallGraphAnalysis
 ; CHECK-O1-NEXT: Running analysis: TargetLibraryAnalysis
 ; CHECK-O-NEXT: Running analysis: FunctionAnalysisManagerCGSCCProxy
 ; CHECK-O-NEXT: Running analysis: OuterAnalysisManagerProxy<{{.*}}LazyCallGraph{{.*}}>
+; CHECK-O23SZ-NEXT: Running pass: PostOrderFunctionAttrsPass
+; CHECK-O23SZ-NEXT: Running pass: ArgumentPromotionPass
+; CHECK-O23SZ-NEXT: Running pass: SROAPass
+; CHECK-O23SZ-NEXT: Running analysis: AssumptionAnalysis on foo
+; CHECK-O23SZ-NEXT: Running pass: IPSCCPPass
+; CHECK-O23SZ-NEXT: Running pass: CalledValuePropagationPass
 ; CHECK-O-NEXT: Running pass: PostOrderFunctionAttrsPass
 ; CHECK-O-NEXT: Running analysis: AAManager
 ; CHECK-O-NEXT: Running analysis: BasicAA