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[CUDA][HIP] Mark device var used by host only 

Add device variables to llvm.compiler.used if they are
ODR-used by either host or device functions.

This is necessary to prevent them from being
eliminated by whole-program optimization
where the compiler has no way to know a device
variable is used by some host code.

Reviewed by: Artem Belevich

Differential Revision: https://reviews.llvm.org/D98814
This commit is contained in:
Yaxun (Sam) Liu 2021-03-17 16:14:03 -04:00
parent 3597f02fd5
commit d5c0f00e21
2 changed files with 69 additions and 0 deletions
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22
clang/lib/CodeGen/CGCUDANV.cpp
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@ -1089,6 +1089,28 @@ void CGNVCUDARuntime::transformManagedVars() {
llvm::Function *CGNVCUDARuntime::finalizeModule() { llvm::Function *CGNVCUDARuntime::finalizeModule() {
if (CGM.getLangOpts().CUDAIsDevice) { if (CGM.getLangOpts().CUDAIsDevice) {
transformManagedVars(); transformManagedVars();
// Mark ODR-used device variables as compiler used to prevent it from being
// eliminated by optimization. This is necessary for device variables
// ODR-used by host functions. Sema correctly marks them as ODR-used no
// matter whether they are ODR-used by device or host functions.
//
// We do not need to do this if the variable has used attribute since it
// has already been added.
//
// Static device variables have been externalized at this point, therefore
// variables with LLVM private or internal linkage need not be added.
for (auto &&Info : DeviceVars) {
auto Kind = Info.Flags.getKind();
if (!Info.Var->isDeclaration() &&
!llvm::GlobalValue::isLocalLinkage(Info.Var->getLinkage()) &&
(Kind == DeviceVarFlags::Variable ||
Kind == DeviceVarFlags::Surface ||
Kind == DeviceVarFlags::Texture) &&
Info.D->isUsed() && !Info.D->hasAttr<UsedAttr>()) {
CGM.addCompilerUsedGlobal(Info.Var);
}
}
return nullptr; return nullptr;
} }
return makeModuleCtorFunction(); return makeModuleCtorFunction();

47
clang/test/CodeGenCUDA/host-used-device-var.cu Normal file
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@ -0,0 +1,47 @@
// REQUIRES: amdgpu-registered-target
// RUN: %clang_cc1 -triple amdgcn-amd-amdhsa -fcuda-is-device -x hip %s \
// RUN: -std=c++11 -O3 -mllvm -amdgpu-internalize-symbols -emit-llvm -o - \
// RUN: | FileCheck %s
#include "Inputs/cuda.h"
// Check device variables used by neither host nor device functioins are not kept.
// CHECK-NOT: @v1
__device__ int v1;
// CHECK-NOT: @v2
__constant__ int v2;
// CHECK-NOT: @_ZL2v3
static __device__ int v3;
// Check device variables used by host functions are kept.
// CHECK-DAG: @u1
__device__ int u1;
// CHECK-DAG: @u2
__constant__ int u2;
// Check host-used static device var is in llvm.compiler.used.
// CHECK-DAG: @_ZL2u3
static __device__ int u3;
// Check device-used static device var is emitted but is not in llvm.compiler.used.
// CHECK-DAG: @_ZL2u4
static __device__ int u4;
// Check device variables with used attribute are always kept.
// CHECK-DAG: @u5
__device__ __attribute__((used)) int u5;
int fun1() {
return u1 + u2 + u3;
}
__global__ void kern1(int **x) {
*x = &u4;
}
// Check the exact list of variables to ensure @_ZL2u4 is not among them.
// CHECK: @llvm.compiler.used = {{[^@]*}} @_ZL2u3 {{[^@]*}} @u1 {{[^@]*}} @u2 {{[^@]*}} @u5