[llvm] [PassBuilder] Add a pass to LTO postlink step (PR #124053)

[via llvm-commits]

https://github.com/gulfemsavrun updated https://github.com/llvm/llvm-project/pull/124053

>From 73aa22554d1108f9bee25c6f5d5371ce01369eef Mon Sep 17 00:00:00 2001
From: Gulfem Savrun Yeniceri <gulfem at google.com>
Date: Wed, 22 Jan 2025 18:49:30 -0800
Subject: [PATCH] [PassBuilder] Add RelLookupTableConverterPass to LTO

This patch adds RelLookupTableConverterPass into the LTO
post-link optimization pass pipeline. This optimization
converts lookup tables to relative lookup tables to make
them PIC-friendly, which is already included in the non-LTO
pass pipeline. This patch adds this optimization to the
post-link optimization pipeline to discover more
opportunities in the LTO context.
---
 llvm/docs/ReleaseNotes.md                | 2 ++
 llvm/lib/Passes/PassBuilderPipelines.cpp | 6 +++---
 llvm/test/Other/new-pm-lto-defaults.ll   | 1 +
 3 files changed, 6 insertions(+), 3 deletions(-)

diff --git a/llvm/docs/ReleaseNotes.md b/llvm/docs/ReleaseNotes.md
index 48f962d212e86d..d69ca9ff643604 100644
--- a/llvm/docs/ReleaseNotes.md
+++ b/llvm/docs/ReleaseNotes.md
@@ -127,6 +127,8 @@ Changes to TableGen
 Changes to Interprocedural Optimizations
 ----------------------------------------
 
+* Added RelLookupTableConverterPass to LTO post-link pass pipeline.
+
 Changes to the AArch64 Backend
 ------------------------------
 
diff --git a/llvm/lib/Passes/PassBuilderPipelines.cpp b/llvm/lib/Passes/PassBuilderPipelines.cpp
index 4ec0fb8fc81ea4..17ff3bd37884b7 100644
--- a/llvm/lib/Passes/PassBuilderPipelines.cpp
+++ b/llvm/lib/Passes/PassBuilderPipelines.cpp
@@ -1594,9 +1594,7 @@ PassBuilder::buildModuleOptimizationPipeline(OptimizationLevel Level,
     MPM.addPass(CGProfilePass(LTOPhase == ThinOrFullLTOPhase::FullLTOPostLink ||
                               LTOPhase == ThinOrFullLTOPhase::ThinLTOPostLink));
 
-  // TODO: Relative look table converter pass caused an issue when full lto is
-  // enabled. See https://reviews.llvm.org/D94355 for more details.
-  // Until the issue fixed, disable this pass during pre-linking phase.
+  // RelLookupTableConverterPass runs later in LTO post-link pipeline.
   if (!LTOPreLink)
     MPM.addPass(RelLookupTableConverterPass());
 
@@ -2121,6 +2119,8 @@ PassBuilder::buildLTODefaultPipeline(OptimizationLevel Level,
   if (PTO.MergeFunctions)
     MPM.addPass(MergeFunctionsPass());
 
+  MPM.addPass(RelLookupTableConverterPass());
+
   if (PTO.CallGraphProfile)
     MPM.addPass(CGProfilePass(/*InLTOPostLink=*/true));
 
diff --git a/llvm/test/Other/new-pm-lto-defaults.ll b/llvm/test/Other/new-pm-lto-defaults.ll
index f788db1e338a1e..59d9ee24527b64 100644
--- a/llvm/test/Other/new-pm-lto-defaults.ll
+++ b/llvm/test/Other/new-pm-lto-defaults.ll
@@ -146,6 +146,7 @@
 ; CHECK-O23SZ-NEXT: Running pass: SimplifyCFGPass
 ; CHECK-O23SZ-NEXT: Running pass: EliminateAvailableExternallyPass
 ; CHECK-O23SZ-NEXT: Running pass: GlobalDCEPass
+; CHECK-O23SZ-NEXT: Running pass: RelLookupTableConverterPass
 ; CHECK-O23SZ-NEXT: Running pass: CGProfilePass
 ; CHECK-EP-NEXT: Running pass: NoOpModulePass
 ; CHECK-O-NEXT: Running pass: AnnotationRemarksPass on foo