MaskRay created this revision.
MaskRay added reviewers: jlebar, tra.
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Herald added a project: clang.
MaskRay requested review of this revision.
Host-side shadow variables of external declarations of device-side global
variables have internal linkage and are referenced by `__cuda_register_globals`.
If such a variable has a comdat group (e.g. a C++17 inline variable), we need to
suppress the comdat group when the linkage is changed to internal (which
represents a local symbol), because:
- the copy in this translation unit can be discarded (a copy from another
translation unit is picked)
- accessing a discarded local symbol from outside the section group is
disallowed by the ELF specification:
> A symbol table entry with STB_LOCAL binding that is defined relative to one
> of a group's sections, and that is contained in a symbol table section that
> is not part of the group, must be discarded if the group members are
> discarded. References to this symbol table entry from outside the group are
> not allowed.
Repository:
rG LLVM Github Monorepo
https://reviews.llvm.org/D88786
Files:
clang/lib/CodeGen/CodeGenModule.cpp
clang/test/CodeGenCUDA/device-stub.cu
Index: clang/test/CodeGenCUDA/device-stub.cu
===
--- clang/test/CodeGenCUDA/device-stub.cu
+++ clang/test/CodeGenCUDA/device-stub.cu
@@ -29,6 +29,10 @@
// RUN: -target-sdk-version=9.2 -fgpu-rdc -fcuda-include-gpubinary %t -o -
\
// RUN: | FileCheck %s -allow-deprecated-dag-overlap \
// RUN: --check-prefixes=ALL,LNX,RDC,CUDA,CUDARDC,CUDA_NEW
+// RUN: %clang_cc1 -triple x86_64-linux-gnu -emit-llvm %s -std=c++17 \
+// RUN: -target-sdk-version=9.2 -fgpu-rdc -fcuda-include-gpubinary %t -o -
\
+// RUN: | FileCheck %s -allow-deprecated-dag-overlap \
+// RUN: --check-prefixes=ALL,LNX,RDC,CUDA,CUDARDC,CUDA_NEW,LNX_17
// RUN: %clang_cc1 -triple x86_64-linux-gnu -emit-llvm %s \
// RUN: -target-sdk-version=9.2 -o - \
// RUN: | FileCheck -allow-deprecated-dag-overlap %s -check-prefix=NOGPUBIN
@@ -91,9 +95,17 @@
// WIN-DAG: @"?ext_constant_var_def@@3HA" = internal global i32 undef
__constant__ int ext_constant_var_def = 2;
+#if __cplusplus > 201402L
+/// The local symbol _ZN1C10inline_varE cannot have a comdat, because it is
+/// referenced from a section (__cuda_module_ctor's section) outside the
section group.
+// LNX_17: @_ZN1C10inline_varE = internal constant i32 undef, align 4{{$}}
+struct C {
+ __device__ static constexpr int inline_var = 17;
+};
+#endif
void use_pointers() {
- int *p;
+ const int *p;
p = &device_var;
p = &constant_var;
p = &shared_var;
@@ -101,6 +113,9 @@
p = &ext_device_var;
p = &ext_constant_var;
p = &ext_host_var;
+#if __cplusplus > 201402L
+ p = &C::inline_var;
+#endif
}
// Make sure that all parts of GPU code init/cleanup are there:
@@ -185,6 +200,7 @@
// ALL-DAG: call void {{.*}}[[PREFIX]]RegisterVar(i8** %0,
{{.*}}constant_var{{[^,]*}}, {{[^@]*}}@2, {{.*}}i32 0, {{i32|i64}} 4, i32 1,
i32 0
// ALL-DAG: call void {{.*}}[[PREFIX]]RegisterVar(i8** %0,
{{.*}}ext_device_var_def{{[^,]*}}, {{[^@]*}}@3, {{.*}}i32 0, {{i32|i64}} 4, i32
0, i32 0
// ALL-DAG: call void {{.*}}[[PREFIX]]RegisterVar(i8** %0,
{{.*}}ext_constant_var_def{{[^,]*}}, {{[^@]*}}@4, {{.*}}i32 0, {{i32|i64}} 4,
i32 1, i32 0
+// LNX_17: call void {{.*}}[[PREFIX]]RegisterVar(i8** %0,
{{.*}}@_ZN1C10inline_varE{{[^,]*}}, {{[^@]*}}@5, {{.*}}i32 0, {{i32|i64}} 4,
i32 0, i32 0
// ALL: ret void
// Test that we've built a constructor.
Index: clang/lib/CodeGen/CodeGenModule.cpp
===
--- clang/lib/CodeGen/CodeGenModule.cpp
+++ clang/lib/CodeGen/CodeGenModule.cpp
@@ -4114,6 +4114,7 @@
// Is accessible from all the threads within the grid and from the host
// through the runtime library (cudaGetSymbolAddress() / cudaGetSymbolSize()
// / cudaMemcpyToSymbol() / cudaMemcpyFromSymbol())."
+ bool CudaModuleCtorReferenced = false;
if (GV && LangOpts.CUDA) {
if (LangOpts.CUDAIsDevice) {
if (Linkage != llvm::GlobalValue::InternalLinkage &&
@@ -4128,10 +4129,16 @@
Linkage = llvm::GlobalValue::InternalLinkage;
// Shadow variables and their properties must be registered with CUDA
// runtime. Skip Extern global variables, which will be registered in
-// the TU where they are defined.
-if (!D->hasExternalStorage())
+// the TU where they are defined. The variable cannot be placed in a
+// comdat, because the copy in this translation unit can be discarded
+// and referencing a discarded local symbol from outside the comdat
+// (__cuda_module_ctor is in a different section) is disallowed by the
+// ELF spec.
+if (!D->hasExternalStorage()) {
getCUDARuntime().registerDeviceVar(D, *GV, !D->hasDefinition(),
