[GlobalMerge] Update the GlobalMerge pass to merge private global variables.

[amy-kwan]

This patch updates the GlobalMerge pass to be able to handle private global variables, which is required for a follow-up PowerPC specific GlobalMerge patch to merge internal and private globals.

A new LIT test is also added to exhibit the ability to merge private globals.

[llvmbot]

@llvm/pr-subscribers-llvm-transforms

Author: Amy Kwan (amy-kwan)

Changes

This patch updates the GlobalMerge pass to be able to handle private global variables, which is required for a follow-up PowerPC specific GlobalMerge patch to merge internal and private globals.

A new LIT test is also added to exhibit the ability to merge private globals.

---

Full diff: https://github.com/llvm/llvm-project/pull/101222.diff

2 Files Affected:

• (modified) llvm/lib/CodeGen/GlobalMerge.cpp (+1-1)
• (added) llvm/test/Transforms/GlobalMerge/private-global.ll (+31)

diff --git a/llvm/lib/CodeGen/GlobalMerge.cpp b/llvm/lib/CodeGen/GlobalMerge.cpp
index 65bf7161441ba..e420c2bb7a25e 100644
--- a/llvm/lib/CodeGen/GlobalMerge.cpp
+++ b/llvm/lib/CodeGen/GlobalMerge.cpp
@@ -664,7 +664,7 @@ bool GlobalMergeImpl::run(Module &M) {
       continue;
 
     if (!(Opt.MergeExternal && GV.hasExternalLinkage()) &&
-        !GV.hasInternalLinkage())
+        !GV.hasInternalLinkage() && !GV.hasPrivateLinkage())
       continue;
 
     PointerType *PT = dyn_cast<PointerType>(GV.getType());
diff --git a/llvm/test/Transforms/GlobalMerge/private-global.ll b/llvm/test/Transforms/GlobalMerge/private-global.ll
new file mode 100644
index 0000000000000..f0ff89061f07c
--- /dev/null
+++ b/llvm/test/Transforms/GlobalMerge/private-global.ll
@@ -0,0 +1,31 @@
+; RUN: opt -global-merge -global-merge-max-offset=100 -S -o - %s | FileCheck %s
+; RUN: opt -passes='global-merge<max-offset=100>' -S -o - %s | FileCheck %s
+
+; NOTE: This is a copy of the llvm/test/Transforms/GlobalMerge/used.ll test,
+; using `private` global variables instead of `internal`. This is to show that
+; that private globals can be merged in the GlobalMerge pass.
+
+target datalayout = "e-p:64:64"
+target triple = "x86_64-unknown-linux-gnu"
+
+; CHECK: @_MergedGlobals = private global <{ i32, i32 }> <{ i32 3, i32 3 }>, align 4
+
+@a = private global i32 1
+@b = private global i32 2
+@c = private global i32 3
+@d = private global i32 3
+
+@llvm.used = appending global [1 x ptr] [ptr @a], section "llvm.metadata"
+@llvm.compiler.used = appending global [1 x ptr] [ptr @b], section "llvm.metadata"
+
+define void @use_private() {
+  ; CHECK: load i32, ptr @a
+  %x = load i32, ptr @a
+  ; CHECK: load i32, ptr @b
+  %y = load i32, ptr @b
+  ; CHECK: load i32, ptr @_MergedGlobals
+  %z1 = load i32, ptr @c
+  ; CHECK: load i32, ptr getelementptr inbounds (<{ i32, i32 }>, ptr @_MergedGlobals, i32 0, i32 1)
+  %z2 = load i32, ptr @d
+  ret void
+}

[chenzheng1030]

LGTM.

[nikic]

LGTM, but I think it would make more sense to base your test on basic.ll rather than used.ll, as the latter tests specific interaction with llvm.used globals, which is orthogonal to private visibility.

[amy-kwan]

LGTM, but I think it would make more sense to base your test on basic.ll rather than used.ll, as the latter tests specific interaction with llvm.used globals, which is orthogonal to private visibility.

Thanks for the good suggestion. I've updated the LIT test.