[clang] [CIR] Don't double-init global variables anymore. (PR #230279)

[Erich Keane via cfe-commits]

https://github.com/erichkeane created https://github.com/llvm/llvm-project/pull/230279

My last patch, #228586, did some additional work to make sure we properly initialized globals even if they had multiple blocks in their initializer rather than assuming there was one.

As a result, the dynamic initialization of a variable referenced multiple times regressed, as we started failing verification because we are double-emitting the initializer.

Note we ALWAYS double-emitted the initializer, but we replaced it every time. The change above caused us to re-use the same set of blocks to better tolerate multiple blocks, and as a side effect, the second block initialization added instead of replacing.

This patch fixes this by making sure we only define a global variable if it isn't yet defined.

>From c02717f3dd72f4e26a810c264e7b4ef845fc4439 Mon Sep 17 00:00:00 2001
From: erichkeane <ekeane at nvidia.com>
Date: Thu, 8 Oct 2026 13:45:59 -0700
Subject: [PATCH] [CIR] Don't double-init global variables anymore.

My last patch, #228586, did some additional work to make sure we
properly initialized globals even if they had multiple blocks in their
initializer rather than assuming there was one.

As a result, the dynamic initialization of a variable referenced
multiple times regressed, as we started failing verification because we
are double-emitting the initializer.

Note we ALWAYS double-emitted the initializer, but we replaced it every
time. The change above caused us to re-use the same set of blocks to
better tolerate multiple blocks, and as a side effect, the second block
initialization added instead of replacing.

This patch fixes this by making sure we only define a global variable if
it isn't yet defined.
---
 clang/lib/CIR/CodeGen/CIRGenModule.cpp        |  7 ++++
 .../CIR/CodeGen/global-var-template-ctor.cpp  | 40 ++++++++++++++-----
 2 files changed, 36 insertions(+), 11 deletions(-)

diff --git a/clang/lib/CIR/CodeGen/CIRGenModule.cpp b/clang/lib/CIR/CodeGen/CIRGenModule.cpp
index 1b17ad636829d5..f399bfd3b30459 100644
--- a/clang/lib/CIR/CodeGen/CIRGenModule.cpp
+++ b/clang/lib/CIR/CodeGen/CIRGenModule.cpp
@@ -673,6 +673,13 @@ void CIRGenModule::emitGlobal(clang::GlobalDecl gd) {
   // to benefit from cache locality. Deferring code generation is necessary to
   // avoid adding initializers to external declarations.
   if (mustBeEmitted(global) && mayBeEmittedEagerly(global)) {
+    // Make sure we don't double-emit this declaration.
+    if (auto existing = dyn_cast_if_present<cir::CIRGlobalValueInterface>(
+            getGlobalValue(getMangledName(gd)));
+        existing && !existing.isDeclaration())
+      if (!existing.isDeclaration())
+        return;
+
     // Emit the definition if it can't be deferred.
     emitGlobalDefinition(gd);
     return;
diff --git a/clang/test/CIR/CodeGen/global-var-template-ctor.cpp b/clang/test/CIR/CodeGen/global-var-template-ctor.cpp
index a01d7d7431a32f..dae27e4415ce1e 100644
--- a/clang/test/CIR/CodeGen/global-var-template-ctor.cpp
+++ b/clang/test/CIR/CodeGen/global-var-template-ctor.cpp
@@ -1,9 +1,9 @@
 // RUN: %clang_cc1 -std=c++14 -triple x86_64-unknown-linux-gnu -fclangir -emit-cir %s -o %t.cir
 // RUN: FileCheck --check-prefix=CIR --input-file=%t.cir %s
 // RUN: %clang_cc1 -std=c++14 -triple x86_64-unknown-linux-gnu -fclangir -emit-llvm %s -o %t-cir.ll
-// RUN: FileCheck --check-prefix=LLVM --input-file=%t-cir.ll %s
+// RUN: FileCheck --check-prefix=LLVM,LLVMCIR --input-file=%t-cir.ll %s
 // RUN: %clang_cc1 -std=c++14 -triple x86_64-unknown-linux-gnu -emit-llvm %s -o %t.ll
-// RUN: FileCheck --check-prefix=OGCG --input-file=%t.ll %s
+// RUN: FileCheck --check-prefix=LLVM,OGCG --input-file=%t.ll %s
 
 // Regression test: C++14 variable templates with non-constexpr
 // constructors must not crash CIR with "ctorRegion failed to
@@ -23,14 +23,32 @@ int test() {
   return fix<1> + fix<2>;
 }
 
-// CIR: cir.global "private" internal dso_local @_ZL3fixILi1EE
-// CIR: cir.global "private" internal dso_local @_ZL3fixILi2EE
-// CIR: cir.func {{.*}} @_Z4testv
+// make sure we only emit the initializer 1x, even if it is used 2x.
+int get_value();
+template<int N> int dyn = get_value();
 
-// LLVM: @_ZL3fixILi1EE = internal global
-// LLVM: @_ZL3fixILi2EE = internal global
-// LLVM: define {{.*}} @_Z4testv
+int test_multi_use() {
+  return dyn<1> + dyn<1>;
+}
+// CIR-DAG: cir.global "private" internal  dso_local @_ZL3fixILi1EE = #cir.zero : !rec_FixedInt3C13E
+// CIR-DAG: cir.global "private" internal  dso_local @_ZL3fixILi2EE = #cir.zero : !rec_FixedInt3C23E
+// CIR-DAG: cir.global linkonce_odr comdat dynamic_init_guard<"_ZGV3dynILi1EE"> @_Z3dynILi1EE = #cir.int<0> : !s32i 
+
+// LLVM-DAG: @_ZL3fixILi1EE = internal global %{{.*}}FixedInt{{.*}} zeroinitializer
+// LLVM-DAG: @_ZL3fixILi2EE = internal global %{{.*}}FixedInt{{.*}} zeroinitializer
+// LLVM-DAG: @_ZGV3dynILi1EE = linkonce_odr global i64 0, comdat($_Z3dynILi1EE)
+
+// Classic orderes this first for some reason, so we have to have a separate
+// check line.
+// OGCG-DAG: define {{.*}} @_Z4testv
+
+// CIR-LABEL: cir.func comdat("_Z3dynILi1EE") {{.*}}@__cxx_global_var_init
+// CIR:   cir.call @_Z9get_valuev()
+// CIR-NOT: cir.call @_Z9get_valuev()
+
+// LLVM-LABEL: define internal void @__cxx_global_var_init{{.*}}() {{.*}}comdat($_Z3dynILi1EE) {
+// LLVM: call {{.*}}@_Z9get_valuev()
+// LLVM-NOT: call {{.*}}@_Z9get_valuev()
 
-// OGCG: @_ZL3fixILi1EE = internal global
-// OGCG: @_ZL3fixILi2EE = internal global
-// OGCG: define {{.*}} @_Z4testv
+// CIR-DAG: cir.func {{.*}} @_Z4testv
+// LLVMCIR-DAG: define {{.*}} @_Z4testv