[clang] 90c90a4 - [CIR] Initialization of global atomic variables (#194239)

[via cfe-commits]

Author: Sirui Mu
Date: 2026-04-28T20:22:53+08:00
New Revision: 90c90a41bed5ba2e4c7b724ecfd533f6f3f7d204

URL: https://github.com/llvm/llvm-project/commit/90c90a41bed5ba2e4c7b724ecfd533f6f3f7d204
DIFF: https://github.com/llvm/llvm-project/commit/90c90a41bed5ba2e4c7b724ecfd533f6f3f7d204.diff

LOG: [CIR] Initialization of global atomic variables (#194239)

This patch adds support for initializing global atomic variables. It
does not include support for tail paddings, which will be added in later
patches.

Assisted-by: Codex / GPT-5.5

Added: 
    

Modified: 
    clang/include/clang/CIR/MissingFeatures.h
    clang/lib/CIR/CodeGen/CIRGenExprConstant.cpp
    clang/test/CIR/CodeGen/atomic.c

Removed: 
    


################################################################################
diff  --git a/clang/include/clang/CIR/MissingFeatures.h b/clang/include/clang/CIR/MissingFeatures.h
index 9afe62437b6da..eea858e3aa8cb 100644
--- a/clang/include/clang/CIR/MissingFeatures.h
+++ b/clang/include/clang/CIR/MissingFeatures.h
@@ -173,6 +173,7 @@ struct MissingFeatures {
   static bool atomicUseLibCall() { return false; }
   static bool atomicMicrosoftVolatile() { return false; }
   static bool atomicOpenMP() { return false; }
+  static bool atomicInitTailPadding() { return false; }
 
   // Global ctor handling
   static bool globalCtorLexOrder() { return false; }

diff  --git a/clang/lib/CIR/CodeGen/CIRGenExprConstant.cpp b/clang/lib/CIR/CodeGen/CIRGenExprConstant.cpp
index 438f99246306e..490703d9b5052 100644
--- a/clang/lib/CIR/CodeGen/CIRGenExprConstant.cpp
+++ b/clang/lib/CIR/CodeGen/CIRGenExprConstant.cpp
@@ -1744,21 +1744,24 @@ mlir::Attribute ConstantEmitter::emitNullForMemory(mlir::Location loc,
 
 mlir::Attribute ConstantEmitter::emitForMemory(mlir::Attribute c,
                                                QualType destType) {
-  // For an _Atomic-qualified constant, we may need to add tail padding.
-  if (destType->getAs<AtomicType>()) {
-    cgm.errorNYI("emitForMemory: atomic type");
-    return {};
-  }
-
-  return c;
+  return emitForMemory(cgm, c, destType);
 }
 
 mlir::Attribute ConstantEmitter::emitForMemory(CIRGenModule &cgm,
                                                mlir::Attribute c,
                                                QualType destType) {
   // For an _Atomic-qualified constant, we may need to add tail padding.
-  if (destType->getAs<AtomicType>()) {
-    cgm.errorNYI("atomic constants");
+  if (const auto *at = destType->getAs<AtomicType>()) {
+    QualType destValueType = at->getValueType();
+    c = emitForMemory(cgm, c, destValueType);
+
+    uint64_t innerSize = cgm.getASTContext().getTypeSize(destValueType);
+    uint64_t outerSize = cgm.getASTContext().getTypeSize(destType);
+    if (innerSize == outerSize)
+      return c;
+
+    assert(innerSize < outerSize && "emitted over-large constant for atomic");
+    cgm.errorNYI("emitForMemory: tail padding in atomic initializer");
   }
 
   return c;

diff  --git a/clang/test/CIR/CodeGen/atomic.c b/clang/test/CIR/CodeGen/atomic.c
index abce1166cf9a2..e6e45e787a37c 100644
--- a/clang/test/CIR/CodeGen/atomic.c
+++ b/clang/test/CIR/CodeGen/atomic.c
@@ -5,6 +5,17 @@
 // RUN: %clang_cc1 -triple x86_64-unknown-linux-gnu -Wno-unused-value -emit-llvm %s -o %t.ll
 // RUN: FileCheck --input-file=%t.ll %s -check-prefix=OGCG
 
+_Atomic int g1;
+_Atomic int g2 = 42;
+// CIR: cir.global external @g2 = #cir.int<42> : !s32i {alignment = 4 : i64}
+// CIR: cir.global external @g1 = #cir.int<0> : !s32i {alignment = 4 : i64}
+
+// LLVM: @g2 = global i32 42, align 4
+// LLVM: @g1 = global i32 0, align 4
+
+// OGCG: @g2 = global i32 42, align 4
+// OGCG: @g1 = global i32 0, align 4
+
 void f1(void) {
   _Atomic(int) x = 42;
 }