[llvm] [GlobalMerge]Prefer use global-merge-max-offset instead of the target-specific constant offset. (PR #165591)

[via llvm-commits]

https://github.com/hstk30-hw updated https://github.com/llvm/llvm-project/pull/165591

>From dfe52c56e3a45698570307a4e6876b562944dabe Mon Sep 17 00:00:00 2001
From: hstk30-hw <hanwei62 at huawei.com>
Date: Wed, 29 Oct 2025 23:57:58 +0800
Subject: [PATCH 1/2] Prefer use global-merge-max-offset instead of the
 target-specific constant offset.

In the Dhrystone benchmark, I find some adjacent global not be merged, on
the contrary the GCC's anchor optimize is work. Use
global-merge-max-offset to set the max offset can yield similar results
(still slightly different)
---
 llvm/lib/CodeGen/GlobalMerge.cpp | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/llvm/lib/CodeGen/GlobalMerge.cpp b/llvm/lib/CodeGen/GlobalMerge.cpp
index e58d7e344c28b..3683cbe596eda 100644
--- a/llvm/lib/CodeGen/GlobalMerge.cpp
+++ b/llvm/lib/CodeGen/GlobalMerge.cpp
@@ -772,6 +772,7 @@ Pass *llvm::createGlobalMergePass(const TargetMachine *TM, unsigned Offset,
   bool MergeConstAggressive = GlobalMergeAllConst.getNumOccurrences() > 0
                                   ? GlobalMergeAllConst
                                   : MergeConstAggressiveByDefault;
-  return new GlobalMerge(TM, Offset, OnlyOptimizeForSize, MergeExternal,
+  unsigned PreferOffset = GlobalMergeMaxOffset ? GlobalMergeMaxOffset : Offset;
+  return new GlobalMerge(TM, PerferOffset, OnlyOptimizeForSize, MergeExternal,
                          MergeConstant, MergeConstAggressive);
 }

>From 504be520b629857ec3f37154a18a2ad815ed3b90 Mon Sep 17 00:00:00 2001
From: hstk30-hw <hanwei62 at huawei.com>
Date: Thu, 30 Oct 2025 09:41:21 +0800
Subject: [PATCH 2/2] Update GlobalMerge.cpp

---
 llvm/lib/CodeGen/GlobalMerge.cpp | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/llvm/lib/CodeGen/GlobalMerge.cpp b/llvm/lib/CodeGen/GlobalMerge.cpp
index 3683cbe596eda..b0b249b54d6fe 100644
--- a/llvm/lib/CodeGen/GlobalMerge.cpp
+++ b/llvm/lib/CodeGen/GlobalMerge.cpp
@@ -773,6 +773,6 @@ Pass *llvm::createGlobalMergePass(const TargetMachine *TM, unsigned Offset,
                                   ? GlobalMergeAllConst
                                   : MergeConstAggressiveByDefault;
   unsigned PreferOffset = GlobalMergeMaxOffset ? GlobalMergeMaxOffset : Offset;
-  return new GlobalMerge(TM, PerferOffset, OnlyOptimizeForSize, MergeExternal,
+  return new GlobalMerge(TM, PreferOffset, OnlyOptimizeForSize, MergeExternal,
                          MergeConstant, MergeConstAggressive);
 }