https://github.com/shiltian created
https://github.com/llvm/llvm-project/pull/134476
In HIP, the Clang driver already sets `force-import-all` when ThinLTO is
enabled. As a result, all imported functions get the `available_externally`
linkage. However, these functions are later removed by the
`EliminateAvailableExternallyPass`, effectively undoing the forced import and
eventually leading to link errors.
The `EliminateAvailableExternallyPass` provides an option to convert
`available_externally` functions into local functions, renaming them to avoid
conflicts. This behavior is exactly what we need for HIP. This PR enables that
option (`avail-extern-to-local`) alongside `force-import-all` when ThinLTO is
used.
With this change, ThinLTO almost works correctly on AMDGPU. The only remaining
issue is an undefined reference to `__assert_fail`, but that falls outside the
scope of this PR.
>From 14237920a276bdea7d5654bad738a5109b7629fc Mon Sep 17 00:00:00 2001
From: Shilei Tian <i...@tianshilei.me>
Date: Fri, 4 Apr 2025 22:58:18 -0400
Subject: [PATCH] [Clang][AMDGPU] Enable `avail-extern-to-local` for ThinLTO in
HIP
In HIP, the Clang driver already sets `force-import-all` when ThinLTO is
enabled. As a result, all imported functions get the `available_externally`
linkage. However, these functions are later removed by the
`EliminateAvailableExternallyPass`, effectively undoing the forced import and
eventually leading to link errors.
The `EliminateAvailableExternallyPass` provides an option to convert
`available_externally` functions into local functions, renaming them to avoid
conflicts. This behavior is exactly what we need for HIP. This PR enables that
option (`avail-extern-to-local`) alongside `force-import-all` when ThinLTO is
used.
With this change, ThinLTO almost works correctly on AMDGPU. The only remaining
issue is an undefined reference to `__assert_fail`, but that falls outside the
scope of this PR.
---
clang/lib/Driver/ToolChains/HIPAMD.cpp | 4 +++-
clang/test/Driver/hip-thinlto.hip | 6 ++++++
2 files changed, 9 insertions(+), 1 deletion(-)
create mode 100644 clang/test/Driver/hip-thinlto.hip
diff --git a/clang/lib/Driver/ToolChains/HIPAMD.cpp
b/clang/lib/Driver/ToolChains/HIPAMD.cpp
index abb83701759ce..0c25a40d94a10 100644
--- a/clang/lib/Driver/ToolChains/HIPAMD.cpp
+++ b/clang/lib/Driver/ToolChains/HIPAMD.cpp
@@ -103,8 +103,10 @@ void AMDGCN::Linker::constructLldCommand(Compilation &C,
const JobAction &JA,
// ToDo: Remove this option after AMDGPU backend supports ISA-level linking.
// Since AMDGPU backend currently does not support ISA-level linking, all
// called functions need to be imported.
- if (IsThinLTO)
+ if (IsThinLTO) {
LldArgs.push_back(Args.MakeArgString("-plugin-opt=-force-import-all"));
+
LldArgs.push_back(Args.MakeArgString("-plugin-opt=-avail-extern-to-local"));
+ }
for (const Arg *A : Args.filtered(options::OPT_mllvm)) {
LldArgs.push_back(
diff --git a/clang/test/Driver/hip-thinlto.hip
b/clang/test/Driver/hip-thinlto.hip
new file mode 100644
index 0000000000000..0f5ff58ac547f
--- /dev/null
+++ b/clang/test/Driver/hip-thinlto.hip
@@ -0,0 +1,6 @@
+// RUN: %clang -foffload-lto=thin --offload-link %s -### 2>&1 | FileCheck %s
+
+// CHECK:
"-plugin-opt=-force-import-all"{{.*}}"-plugin-opt=-avail-extern-to-local"
+int main(int, char *[]) {
+ return 0;
+}
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