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merged 1 commit into from
Nov 18, 2025
Merged

[CIR] Add support for common linkage #168613

merged 1 commit into from
Nov 18, 2025

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@andykaylor andykaylor commented Nov 18, 2025

Add support for marking global variables with common linkage.

@andykaylor
[CIR] Add support for common linkage
ba999ae 
Add support for marking global variables with common linkage.
@llvmbot llvmbot added clang Clang issues not falling into any other category ClangIR Anything related to the ClangIR project labels Nov 18, 2025
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llvmbot commented Nov 18, 2025

@llvm/pr-subscribers-clangir

Author: Andy Kaylor (andykaylor)

Changes

Add support for marking global variables with common linkage.

Full diff: https://github.com/llvm/llvm-project/pull/168613.diff

2 Files Affected:

  • (modified) clang/lib/CIR/CodeGen/CIRGenModule.cpp (+12-5)
  • (added) clang/test/CIR/CodeGen/no-common.c (+103)
diff --git a/clang/lib/CIR/CodeGen/CIRGenModule.cpp b/clang/lib/CIR/CodeGen/CIRGenModule.cpp
index 4a82ea3121b60..b8e51f87d4045 100644
--- a/clang/lib/CIR/CodeGen/CIRGenModule.cpp
+++ b/clang/lib/CIR/CodeGen/CIRGenModule.cpp
@@ -883,8 +883,17 @@ void CIRGenModule::emitGlobalVarDefinition(const clang::VarDecl *vd,
   // FIXME(cir): setLinkage should likely set MLIR's visibility automatically.
   gv.setVisibility(getMLIRVisibilityFromCIRLinkage(linkage));
   assert(!cir::MissingFeatures::opGlobalDLLImportExport());
-  if (linkage == cir::GlobalLinkageKind::CommonLinkage)
-    errorNYI(initExpr->getSourceRange(), "common linkage");
+  if (linkage == cir::GlobalLinkageKind::CommonLinkage) {
+    // common vars aren't constant even if declared const.
+    gv.setConstant(false);
+    // Tentative definition of global variables may be initialized with
+    // non-zero null pointers. In this case they should have weak linkage
+    // since common linkage must have zero initializer and must not have
+    // explicit section therefore cannot have non-zero initial value.
+    std::optional<mlir::Attribute> initializer = gv.getInitialValue();
+    if (initializer && !getBuilder().isNullValue(*initializer))
+      gv.setLinkage(cir::GlobalLinkageKind::WeakAnyLinkage);
+  }
 
   setNonAliasAttributes(vd, gv);
 
@@ -1238,10 +1247,8 @@ cir::GlobalLinkageKind CIRGenModule::getCIRLinkageForDeclarator(
   // linkage.
   if (!getLangOpts().CPlusPlus && isa<VarDecl>(dd) &&
       !isVarDeclStrongDefinition(astContext, *this, cast<VarDecl>(dd),
-                                 getCodeGenOpts().NoCommon)) {
-    errorNYI(dd->getBeginLoc(), "common linkage", dd->getDeclKindName());
+                                 getCodeGenOpts().NoCommon))
     return cir::GlobalLinkageKind::CommonLinkage;
-  }
 
   // selectany symbols are externally visible, so use weak instead of
   // linkonce.  MSVC optimizes away references to const selectany globals, so
diff --git a/clang/test/CIR/CodeGen/no-common.c b/clang/test/CIR/CodeGen/no-common.c
new file mode 100644
index 0000000000000..ce4c5fc0b3a33
--- /dev/null
+++ b/clang/test/CIR/CodeGen/no-common.c
@@ -0,0 +1,103 @@
+// RUN: %clang_cc1 -triple x86_64-unknown-linux-gnu -fclangir %s -emit-cir -o %t-default.cir
+// RUN: FileCheck --input-file=%t-default.cir %s -check-prefix=CIR-DEFAULT
+// RUN: %clang_cc1 -triple x86_64-unknown-linux-gnu -fclangir %s -fno-common -emit-cir -o %t-no-common.cir
+// RUN: FileCheck --input-file=%t-no-common.cir %s -check-prefix=CIR-DEFAULT
+// RUN: %clang_cc1 -triple x86_64-unknown-linux-gnu -fclangir %s -fcommon -emit-cir -o %t-common.cir
+// RUN: FileCheck --input-file=%t-common.cir %s -check-prefix=CIR-COMMON
+
+// RUN: %clang_cc1 -triple x86_64-unknown-linux-gnu -fclangir %s -emit-llvm -o %t-default-cir.ll
+// RUN: FileCheck --input-file=%t-default-cir.ll %s -check-prefix=LLVM-DEFAULT
+// RUN: %clang_cc1 -triple x86_64-unknown-linux-gnu -fclangir %s -fno-common -emit-llvm -o %t-no-common-cir.ll
+// RUN: FileCheck --input-file=%t-no-common-cir.ll %s -check-prefix=LLVM-DEFAULT
+// RUN: %clang_cc1 -triple x86_64-unknown-linux-gnu -fclangir %s -fcommon -emit-llvm -o %t-common-cir.ll
+// RUN: FileCheck --input-file=%t-common-cir.ll %s -check-prefix=LLVM-COMMON
+
+// RUN: %clang_cc1 -triple x86_64-unknown-linux-gnu %s -emit-llvm -o %t-default.ll
+// RUN: FileCheck --input-file=%t-default.ll %s -check-prefix=OGCG-DEFAULT
+// RUN: %clang_cc1 -triple x86_64-unknown-linux-gnu %s -fno-common -emit-llvm -o %t-no-common.ll
+// RUN: FileCheck --input-file=%t-no-common.ll %s -check-prefix=OGCG-DEFAULT
+// RUN: %clang_cc1 -triple x86_64-unknown-linux-gnu %s -fcommon -emit-llvm -o %t-common.ll
+// RUN: FileCheck --input-file=%t-common.ll %s -check-prefix=OGCG-COMMON
+
+const int a = 42;
+// CIR-DEFAULT: cir.global constant external @a = #cir.int<42>
+// LLVM-DEFAULT: @a = constant i32 42
+// OGCG-DEFAULT: @a = constant i32 42
+
+// CIR-COMMON: cir.global constant external @a
+// LLVM-COMMON: @a = constant i32 42
+// OGCG-COMMON: @a = constant i32 42
+
+const int b __attribute__((common)) = 42;
+// CIR-DEFAULT: cir.global constant external @b = #cir.int<42>
+// LLVM-DEFAULT: @b = constant i32 42
+// OGCG-DEFAULT: @b = constant i32 42
+
+// CIR-COMMON: cir.global constant external @b = #cir.int<42>
+// LLVM-COMMON: @b = constant i32 42
+// OGCG-COMMON: @b = constant i32 42
+
+const int c __attribute__((nocommon)) = 42;
+// CIR-DEFAULT: cir.global constant external @c = #cir.int<42>
+// LLVM-DEFAULT: @c = constant i32 42
+// OGCG-DEFAULT: @c = constant i32 42
+
+// CIR-COMMON: cir.global constant external @c = #cir.int<42>
+// LLVM-COMMON: @c = constant i32 42
+// OGCG-COMMON: @c = constant i32 42
+
+int d = 11;
+// CIR-DEFAULT: cir.global external @d = #cir.int<11>
+// LLVM-DEFAULT: @d = global i32 11
+// OGCG-DEFAULT: @d = global i32 11
+
+// CIR-COMMON: cir.global external @d = #cir.int<11>
+// LLVM-COMMON: @d = global i32 11
+// OGCG-COMMON: @d = global i32 11
+
+int e;
+// CIR-DEFAULT: cir.global external @e = #cir.int<0>
+// LLVM-DEFAULT: @e = global i32 0
+// OGCG-DEFAULT: @e = global i32 0
+
+// CIR-COMMON: cir.global common @e = #cir.int<0>
+// LLVM-COMMON: @e = common global i32 0
+// OGCG-COMMON: @e = common global i32 0
+
+
+int f __attribute__((common));
+// CIR-DEFAULT: cir.global common @f = #cir.int<0>
+// LLVM-DEFAULT: @f = common global i32 0
+// OGCG-DEFAULT: @f = common global i32 0
+
+// CIR-COMMON: cir.global common @f
+// LLVM-COMMON: @f = common global i32 0
+// OGCG-COMMON: @f = common global i32 0
+
+int g __attribute__((nocommon));
+// CIR-DEFAULT: cir.global external @g = #cir.int<0>
+// LLVM-DEFAULT: @g = global i32
+// OGCG-DEFAULT: @g = global i32 0
+
+// CIR-COMMON: cir.global external @g = #cir.int<0>
+// LLVM-COMMON: @g = global i32 0
+// OGCG-COMMON: @g = global i32 0
+
+const int h;
+// CIR-DEFAULT: cir.global constant external @h = #cir.int<0>
+// LLVM-DEFAULT: @h = constant i32
+// OGCG-DEFAULT: @h = constant i32 0
+
+// CIR-COMMON: cir.global common @h = #cir.int<0>
+// LLVM-COMMON: @h = common global i32 0
+// OGCG-COMMON: @h = common global i32 0
+
+typedef void* (*fn_t)(long a, long b, char *f, int c);
+fn_t ABC __attribute__ ((nocommon));
+// CIR-DEFAULT: cir.global external @ABC = #cir.ptr<null>
+// LLVM-DEFAULT: @ABC = global ptr null
+// OGCG-DEFAULT: @ABC = global ptr null
+
+// CIR-COMMON: cir.global external @ABC = #cir.ptr<null>
+// LLVM-COMMON: @ABC = global ptr null
+// OGCG-COMMON: @ABC = global ptr null

@llvmbot
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llvmbot commented Nov 18, 2025

@llvm/pr-subscribers-clang

Author: Andy Kaylor (andykaylor)

Changes

Add support for marking global variables with common linkage.

Full diff: https://github.com/llvm/llvm-project/pull/168613.diff

2 Files Affected:

  • (modified) clang/lib/CIR/CodeGen/CIRGenModule.cpp (+12-5)
  • (added) clang/test/CIR/CodeGen/no-common.c (+103)
diff --git a/clang/lib/CIR/CodeGen/CIRGenModule.cpp b/clang/lib/CIR/CodeGen/CIRGenModule.cpp
index 4a82ea3121b60..b8e51f87d4045 100644
--- a/clang/lib/CIR/CodeGen/CIRGenModule.cpp
+++ b/clang/lib/CIR/CodeGen/CIRGenModule.cpp
@@ -883,8 +883,17 @@ void CIRGenModule::emitGlobalVarDefinition(const clang::VarDecl *vd,
   // FIXME(cir): setLinkage should likely set MLIR's visibility automatically.
   gv.setVisibility(getMLIRVisibilityFromCIRLinkage(linkage));
   assert(!cir::MissingFeatures::opGlobalDLLImportExport());
-  if (linkage == cir::GlobalLinkageKind::CommonLinkage)
-    errorNYI(initExpr->getSourceRange(), "common linkage");
+  if (linkage == cir::GlobalLinkageKind::CommonLinkage) {
+    // common vars aren't constant even if declared const.
+    gv.setConstant(false);
+    // Tentative definition of global variables may be initialized with
+    // non-zero null pointers. In this case they should have weak linkage
+    // since common linkage must have zero initializer and must not have
+    // explicit section therefore cannot have non-zero initial value.
+    std::optional<mlir::Attribute> initializer = gv.getInitialValue();
+    if (initializer && !getBuilder().isNullValue(*initializer))
+      gv.setLinkage(cir::GlobalLinkageKind::WeakAnyLinkage);
+  }
 
   setNonAliasAttributes(vd, gv);
 
@@ -1238,10 +1247,8 @@ cir::GlobalLinkageKind CIRGenModule::getCIRLinkageForDeclarator(
   // linkage.
   if (!getLangOpts().CPlusPlus && isa<VarDecl>(dd) &&
       !isVarDeclStrongDefinition(astContext, *this, cast<VarDecl>(dd),
-                                 getCodeGenOpts().NoCommon)) {
-    errorNYI(dd->getBeginLoc(), "common linkage", dd->getDeclKindName());
+                                 getCodeGenOpts().NoCommon))
     return cir::GlobalLinkageKind::CommonLinkage;
-  }
 
   // selectany symbols are externally visible, so use weak instead of
   // linkonce.  MSVC optimizes away references to const selectany globals, so
diff --git a/clang/test/CIR/CodeGen/no-common.c b/clang/test/CIR/CodeGen/no-common.c
new file mode 100644
index 0000000000000..ce4c5fc0b3a33
--- /dev/null
+++ b/clang/test/CIR/CodeGen/no-common.c
@@ -0,0 +1,103 @@
+// RUN: %clang_cc1 -triple x86_64-unknown-linux-gnu -fclangir %s -emit-cir -o %t-default.cir
+// RUN: FileCheck --input-file=%t-default.cir %s -check-prefix=CIR-DEFAULT
+// RUN: %clang_cc1 -triple x86_64-unknown-linux-gnu -fclangir %s -fno-common -emit-cir -o %t-no-common.cir
+// RUN: FileCheck --input-file=%t-no-common.cir %s -check-prefix=CIR-DEFAULT
+// RUN: %clang_cc1 -triple x86_64-unknown-linux-gnu -fclangir %s -fcommon -emit-cir -o %t-common.cir
+// RUN: FileCheck --input-file=%t-common.cir %s -check-prefix=CIR-COMMON
+
+// RUN: %clang_cc1 -triple x86_64-unknown-linux-gnu -fclangir %s -emit-llvm -o %t-default-cir.ll
+// RUN: FileCheck --input-file=%t-default-cir.ll %s -check-prefix=LLVM-DEFAULT
+// RUN: %clang_cc1 -triple x86_64-unknown-linux-gnu -fclangir %s -fno-common -emit-llvm -o %t-no-common-cir.ll
+// RUN: FileCheck --input-file=%t-no-common-cir.ll %s -check-prefix=LLVM-DEFAULT
+// RUN: %clang_cc1 -triple x86_64-unknown-linux-gnu -fclangir %s -fcommon -emit-llvm -o %t-common-cir.ll
+// RUN: FileCheck --input-file=%t-common-cir.ll %s -check-prefix=LLVM-COMMON
+
+// RUN: %clang_cc1 -triple x86_64-unknown-linux-gnu %s -emit-llvm -o %t-default.ll
+// RUN: FileCheck --input-file=%t-default.ll %s -check-prefix=OGCG-DEFAULT
+// RUN: %clang_cc1 -triple x86_64-unknown-linux-gnu %s -fno-common -emit-llvm -o %t-no-common.ll
+// RUN: FileCheck --input-file=%t-no-common.ll %s -check-prefix=OGCG-DEFAULT
+// RUN: %clang_cc1 -triple x86_64-unknown-linux-gnu %s -fcommon -emit-llvm -o %t-common.ll
+// RUN: FileCheck --input-file=%t-common.ll %s -check-prefix=OGCG-COMMON
+
+const int a = 42;
+// CIR-DEFAULT: cir.global constant external @a = #cir.int<42>
+// LLVM-DEFAULT: @a = constant i32 42
+// OGCG-DEFAULT: @a = constant i32 42
+
+// CIR-COMMON: cir.global constant external @a
+// LLVM-COMMON: @a = constant i32 42
+// OGCG-COMMON: @a = constant i32 42
+
+const int b __attribute__((common)) = 42;
+// CIR-DEFAULT: cir.global constant external @b = #cir.int<42>
+// LLVM-DEFAULT: @b = constant i32 42
+// OGCG-DEFAULT: @b = constant i32 42
+
+// CIR-COMMON: cir.global constant external @b = #cir.int<42>
+// LLVM-COMMON: @b = constant i32 42
+// OGCG-COMMON: @b = constant i32 42
+
+const int c __attribute__((nocommon)) = 42;
+// CIR-DEFAULT: cir.global constant external @c = #cir.int<42>
+// LLVM-DEFAULT: @c = constant i32 42
+// OGCG-DEFAULT: @c = constant i32 42
+
+// CIR-COMMON: cir.global constant external @c = #cir.int<42>
+// LLVM-COMMON: @c = constant i32 42
+// OGCG-COMMON: @c = constant i32 42
+
+int d = 11;
+// CIR-DEFAULT: cir.global external @d = #cir.int<11>
+// LLVM-DEFAULT: @d = global i32 11
+// OGCG-DEFAULT: @d = global i32 11
+
+// CIR-COMMON: cir.global external @d = #cir.int<11>
+// LLVM-COMMON: @d = global i32 11
+// OGCG-COMMON: @d = global i32 11
+
+int e;
+// CIR-DEFAULT: cir.global external @e = #cir.int<0>
+// LLVM-DEFAULT: @e = global i32 0
+// OGCG-DEFAULT: @e = global i32 0
+
+// CIR-COMMON: cir.global common @e = #cir.int<0>
+// LLVM-COMMON: @e = common global i32 0
+// OGCG-COMMON: @e = common global i32 0
+
+
+int f __attribute__((common));
+// CIR-DEFAULT: cir.global common @f = #cir.int<0>
+// LLVM-DEFAULT: @f = common global i32 0
+// OGCG-DEFAULT: @f = common global i32 0
+
+// CIR-COMMON: cir.global common @f
+// LLVM-COMMON: @f = common global i32 0
+// OGCG-COMMON: @f = common global i32 0
+
+int g __attribute__((nocommon));
+// CIR-DEFAULT: cir.global external @g = #cir.int<0>
+// LLVM-DEFAULT: @g = global i32
+// OGCG-DEFAULT: @g = global i32 0
+
+// CIR-COMMON: cir.global external @g = #cir.int<0>
+// LLVM-COMMON: @g = global i32 0
+// OGCG-COMMON: @g = global i32 0
+
+const int h;
+// CIR-DEFAULT: cir.global constant external @h = #cir.int<0>
+// LLVM-DEFAULT: @h = constant i32
+// OGCG-DEFAULT: @h = constant i32 0
+
+// CIR-COMMON: cir.global common @h = #cir.int<0>
+// LLVM-COMMON: @h = common global i32 0
+// OGCG-COMMON: @h = common global i32 0
+
+typedef void* (*fn_t)(long a, long b, char *f, int c);
+fn_t ABC __attribute__ ((nocommon));
+// CIR-DEFAULT: cir.global external @ABC = #cir.ptr<null>
+// LLVM-DEFAULT: @ABC = global ptr null
+// OGCG-DEFAULT: @ABC = global ptr null
+
+// CIR-COMMON: cir.global external @ABC = #cir.ptr<null>
+// LLVM-COMMON: @ABC = global ptr null
+// OGCG-COMMON: @ABC = global ptr null

andykaylor
andykaylor commented Nov 18, 2025
View reviewed changes
clang/lib/CIR/CodeGen/CIRGenModule.cpp
// explicit section therefore cannot have non-zero initial value.
std::optional<mlir::Attribute> initializer = gv.getInitialValue();
if (initializer && !getBuilder().isNullValue(*initializer))
gv.setLinkage(cir::GlobalLinkageKind::WeakAnyLinkage);
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@andykaylor andykaylor Nov 18, 2025

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The only test case I could find that reaches this requires OpenCL and AMDGCN support, but I think the code is straightforward enough to go in ahead of a test case.

@andykaylor andykaylor merged commit 3e499e9 into llvm:main Nov 18, 2025
11 of 12 checks passed
@andykaylor andykaylor deleted the cir-common-linkage branch November 18, 2025 22:51
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@erichkeane erichkeane erichkeane approved these changes

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