[clang] [CIR][OpenMP] Add emitDeclTargetVarDeclLValue for global variable access (PR #234075)

[Arseniy Obolenskiy via cfe-commits]

https://github.com/aobolensk created https://github.com/llvm/llvm-project/pull/234075

Limit the global access NYI to declare target variables that need indirect access on the device, as OGCG does

>From c76c31e6679a302d7c83a066af103b80bfff4114 Mon Sep 17 00:00:00 2001
From: Arseniy Obolenskiy <arseniy.obolenskiy at amd.com>
Date: Wed, 21 Oct 2026 06:51:18 +0200
Subject: [PATCH] [CIR][OpenMP] Add emitDeclTargetVarDeclLValue for global
 variable access

Limit the global access NYI to declare target variables that need indirect access on the device, as OGCG does
---
 clang/lib/CIR/CodeGen/CIRGenExpr.cpp          | 22 ++++++++++++++--
 clang/lib/CIR/CodeGen/CIRGenOpenMPRuntime.cpp |  7 +++++
 clang/lib/CIR/CodeGen/CIRGenOpenMPRuntime.h   |  3 +++
 .../CIR/CodeGenOpenMP/simd-global-var.cpp     | 26 +++++++++++++++++++
 4 files changed, 56 insertions(+), 2 deletions(-)
 create mode 100644 clang/test/CIR/CodeGenOpenMP/simd-global-var.cpp

diff --git a/clang/lib/CIR/CodeGen/CIRGenExpr.cpp b/clang/lib/CIR/CodeGen/CIRGenExpr.cpp
index dfd6fa725e77fe..654a8733f6930c 100644
--- a/clang/lib/CIR/CodeGen/CIRGenExpr.cpp
+++ b/clang/lib/CIR/CodeGen/CIRGenExpr.cpp
@@ -453,6 +453,21 @@ void CIRGenFunction::emitStoreThroughLValue(RValue src, LValue dst,
   emitStoreOfScalar(src.getValue(), dst, isInit);
 }
 
+static Address emitDeclTargetVarDeclLValue(CIRGenFunction &cgf, const Expr *e,
+                                           const VarDecl *vd) {
+  std::optional<OMPDeclareTargetDeclAttr::MapTypeTy> res =
+      OMPDeclareTargetDeclAttr::isDeclareTargetDeclaration(vd);
+  // MT_Local, and MT_To/MT_Enter without unified memory, use direct access.
+  if (!res || *res == OMPDeclareTargetDeclAttr::MT_Local ||
+      ((*res == OMPDeclareTargetDeclAttr::MT_To ||
+        *res == OMPDeclareTargetDeclAttr::MT_Enter) &&
+       !cgf.cgm.getOpenMPRuntime().hasRequiresUnifiedSharedMemory()))
+    return Address::invalid();
+  cgf.cgm.errorNYI(e->getSourceRange(),
+                   "emitDeclTargetVarDeclLValue: indirect access");
+  return Address::invalid();
+}
+
 static LValue emitGlobalVarDeclLValue(CIRGenFunction &cgf, const Expr *e,
                                       const VarDecl *vd) {
   QualType t = e->getType();
@@ -463,8 +478,11 @@ static LValue emitGlobalVarDeclLValue(CIRGenFunction &cgf, const Expr *e,
 
   // Check if the variable is marked as declare target with link clause in
   // device codegen.
-  if (cgf.getLangOpts().OpenMP)
-    cgf.cgm.errorNYI(e->getSourceRange(), "emitGlobalVarDeclLValue: OpenMP");
+  if (cgf.getLangOpts().OpenMPIsTargetDevice) {
+    Address addr = emitDeclTargetVarDeclLValue(cgf, e, vd);
+    if (addr.isValid())
+      return cgf.makeAddrLValue(addr, t, AlignmentSource::Decl);
+  }
 
   // Traditional LLVM codegen handles thread local separately, CIR handles
   // as part of getAddrOfGlobalVar.
diff --git a/clang/lib/CIR/CodeGen/CIRGenOpenMPRuntime.cpp b/clang/lib/CIR/CodeGen/CIRGenOpenMPRuntime.cpp
index 93ec2248f76eb0..80cae177a341d9 100644
--- a/clang/lib/CIR/CodeGen/CIRGenOpenMPRuntime.cpp
+++ b/clang/lib/CIR/CodeGen/CIRGenOpenMPRuntime.cpp
@@ -16,6 +16,7 @@
 #include "mlir/Dialect/OpenMP/OpenMPDialect.h"
 #include "mlir/Dialect/OpenMP/OpenMPInterfaces.h"
 #include "clang/AST/OpenMPClause.h"
+#include "clang/CIR/MissingFeatures.h"
 
 using namespace clang;
 using namespace clang::CIRGen;
@@ -172,6 +173,12 @@ bool CIRGenOpenMPRuntime::markAsGlobalTarget(GlobalDecl gd) {
   return !alreadyEmittedTargetDecls.insert(d).second;
 }
 
+bool CIRGenOpenMPRuntime::hasRequiresUnifiedSharedMemory() const {
+  // OGCG also sets this from '#pragma omp requires unified_shared_memory'.
+  assert(!cir::MissingFeatures::openMP());
+  return cgm.getLangOpts().OpenMPForceUSM;
+}
+
 void CIRGenOpenMPRuntime::emitDeclareTargetFunction(const FunctionDecl *fd,
                                                     cir::FuncOp funcOp) {
   const auto *attr = fd->getAttr<OMPDeclareTargetDeclAttr>();
diff --git a/clang/lib/CIR/CodeGen/CIRGenOpenMPRuntime.h b/clang/lib/CIR/CodeGen/CIRGenOpenMPRuntime.h
index d22200512e4839..b57537defbfbd0 100644
--- a/clang/lib/CIR/CodeGen/CIRGenOpenMPRuntime.h
+++ b/clang/lib/CIR/CodeGen/CIRGenOpenMPRuntime.h
@@ -48,6 +48,9 @@ class CIRGenOpenMPRuntime {
   /// handled and should be skipped.
   bool markAsGlobalTarget(GlobalDecl gd);
 
+  /// Return whether unified shared memory is required.
+  bool hasRequiresUnifiedSharedMemory() const;
+
   /// If the function has an OMPDeclareTargetDeclAttr, set the corresponding
   /// omp.declare_target attribute on the emitted cir.func op.
   void emitDeclareTargetFunction(const FunctionDecl *fd, cir::FuncOp funcOp);
diff --git a/clang/test/CIR/CodeGenOpenMP/simd-global-var.cpp b/clang/test/CIR/CodeGenOpenMP/simd-global-var.cpp
new file mode 100644
index 00000000000000..3b56fc45493469
--- /dev/null
+++ b/clang/test/CIR/CodeGenOpenMP/simd-global-var.cpp
@@ -0,0 +1,26 @@
+// RUN: %clang_cc1 -fopenmp-simd -triple x86_64-unknown-linux-gnu -fclangir -emit-cir %s -o %t.cir
+// RUN: FileCheck --input-file=%t.cir %s -check-prefix=CIR
+// RUN: %clang_cc1 -fopenmp-simd -triple x86_64-unknown-linux-gnu -fclangir -emit-llvm %s -o %t-cir.ll
+// RUN: FileCheck --input-file=%t-cir.ll %s -check-prefix=LLVM
+// RUN: %clang_cc1 -fopenmp-simd -triple x86_64-unknown-linux-gnu -emit-llvm %s -o %t.ll
+// RUN: FileCheck --input-file=%t.ll %s -check-prefix=LLVM
+
+int g;
+
+// CIR: cir.global external @g = #cir.int<0> : !s32i
+// LLVM: @g = global i32 0
+
+int global_ref(int v) {
+  g = v;
+  return g;
+}
+
+// CIR: cir.func{{.*}} @_Z10global_refi
+// CIR:   %[[G:.*]] = cir.get_global @g : !cir.ptr<!s32i>
+// CIR:   cir.store{{.*}} %{{.*}}, %[[G]] : !s32i, !cir.ptr<!s32i>
+// CIR:   %[[G1:.*]] = cir.get_global @g : !cir.ptr<!s32i>
+// CIR:   %{{.*}} = cir.load{{.*}} %[[G1]] : !cir.ptr<!s32i>, !s32i
+
+// LLVM: define{{.*}} i32 @_Z10global_refi
+// LLVM:   store i32 %{{.*}}, ptr @g
+// LLVM:   %{{.*}} = load i32, ptr @g