[clang][SPIR][SPIRV] Don't generate constant NULL from addrspacecast generic NULL

[wenju-he]

Fix a regression caused by 1ffff05.
OpenCL spec forbids casting between generic and constant address space pointers.

[Copilot]

Pull Request Overview

This PR fixes a regression in SPIR/SPIRV code generation where casting between generic and constant address space pointers was incorrectly allowed, violating the OpenCL specification. The fix ensures that constant address space NULL pointers are generated directly instead of through address space casting from generic NULL.

• Adds explicit handling for opencl_constant address space in the getNullPointer function
• Adds test coverage to verify correct LLVM IR generation for constant address space NULL pointers

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
clang/lib/CodeGen/Targets/SPIR.cpp	Modified getNullPointer to include opencl_constant address space in the condition that returns direct constant NULL pointers
clang/test/CodeGenOpenCL/nullptr.cl	Added new test file to verify correct handling of NULL pointers in constant address space

[llvmbot]

@llvm/pr-subscribers-clang

Author: Wenju He (wenju-he)

Changes

Fix a regression caused by 1ffff05.
OpenCL spec forbids casting between generic and constant address space pointers.

---

Full diff: https://github.com/llvm/llvm-project/pull/165353.diff

2 Files Affected:

• (modified) clang/lib/CodeGen/Targets/SPIR.cpp (+2-1)
• (added) clang/test/CodeGenOpenCL/nullptr.cl (+14)

diff --git a/clang/lib/CodeGen/Targets/SPIR.cpp b/clang/lib/CodeGen/Targets/SPIR.cpp
index 15d0b353d748c..abd049aca0ed7 100644
--- a/clang/lib/CodeGen/Targets/SPIR.cpp
+++ b/clang/lib/CodeGen/Targets/SPIR.cpp
@@ -260,7 +260,8 @@ CommonSPIRTargetCodeGenInfo::getNullPointer(const CodeGen::CodeGenModule &CGM,
   LangAS AS = QT->getUnqualifiedDesugaredType()->isNullPtrType()
                   ? LangAS::Default
                   : QT->getPointeeType().getAddressSpace();
-  if (AS == LangAS::Default || AS == LangAS::opencl_generic)
+  if (AS == LangAS::Default || AS == LangAS::opencl_generic ||
+      AS == LangAS::opencl_constant)
     return llvm::ConstantPointerNull::get(PT);
 
   auto &Ctx = CGM.getContext();
diff --git a/clang/test/CodeGenOpenCL/nullptr.cl b/clang/test/CodeGenOpenCL/nullptr.cl
new file mode 100644
index 0000000000000..6d203fce91dde
--- /dev/null
+++ b/clang/test/CodeGenOpenCL/nullptr.cl
@@ -0,0 +1,14 @@
+// RUN: %clang_cc1 -no-enable-noundef-analysis %s -cl-std=CL2.0 -include opencl-c.h -triple spir64 -emit-llvm -o - | FileCheck %s
+
+// CHECK: @constant_p_NULL =
+// CHECK-SAME: addrspace(1) global ptr addrspace(2) null, align 8
+constant char *constant_p_NULL = NULL;
+
+// CHECK-LABEL: cmp_constant
+// CHECK: icmp eq ptr addrspace(2) %p, null
+char cmp_constant(constant char* p) {
+  if (p != 0)
+    return *p;
+  else
+    return 0;
+}

[llvmbot]

@llvm/pr-subscribers-clang-codegen

Author: Wenju He (wenju-he)

Changes

Fix a regression caused by 1ffff05.
OpenCL spec forbids casting between generic and constant address space pointers.

---

Full diff: https://github.com/llvm/llvm-project/pull/165353.diff

2 Files Affected:

• (modified) clang/lib/CodeGen/Targets/SPIR.cpp (+2-1)
• (added) clang/test/CodeGenOpenCL/nullptr.cl (+14)

diff --git a/clang/lib/CodeGen/Targets/SPIR.cpp b/clang/lib/CodeGen/Targets/SPIR.cpp
index 15d0b353d748c..abd049aca0ed7 100644
--- a/clang/lib/CodeGen/Targets/SPIR.cpp
+++ b/clang/lib/CodeGen/Targets/SPIR.cpp
@@ -260,7 +260,8 @@ CommonSPIRTargetCodeGenInfo::getNullPointer(const CodeGen::CodeGenModule &CGM,
   LangAS AS = QT->getUnqualifiedDesugaredType()->isNullPtrType()
                   ? LangAS::Default
                   : QT->getPointeeType().getAddressSpace();
-  if (AS == LangAS::Default || AS == LangAS::opencl_generic)
+  if (AS == LangAS::Default || AS == LangAS::opencl_generic ||
+      AS == LangAS::opencl_constant)
     return llvm::ConstantPointerNull::get(PT);
 
   auto &Ctx = CGM.getContext();
diff --git a/clang/test/CodeGenOpenCL/nullptr.cl b/clang/test/CodeGenOpenCL/nullptr.cl
new file mode 100644
index 0000000000000..6d203fce91dde
--- /dev/null
+++ b/clang/test/CodeGenOpenCL/nullptr.cl
@@ -0,0 +1,14 @@
+// RUN: %clang_cc1 -no-enable-noundef-analysis %s -cl-std=CL2.0 -include opencl-c.h -triple spir64 -emit-llvm -o - | FileCheck %s
+
+// CHECK: @constant_p_NULL =
+// CHECK-SAME: addrspace(1) global ptr addrspace(2) null, align 8
+constant char *constant_p_NULL = NULL;
+
+// CHECK-LABEL: cmp_constant
+// CHECK: icmp eq ptr addrspace(2) %p, null
+char cmp_constant(constant char* p) {
+  if (p != 0)
+    return *p;
+  else
+    return 0;
+}