[clang] fcf0f81 - [Clang][AMDGPU] Enable `avail-extern-to-local` for ThinLTO in HIP (#134476)

[via cfe-commits]

Author: Shilei Tian
Date: 2025-04-14T11:52:19-04:00
New Revision: fcf0f810ac4b22bda3f21048784ee114da1cb061

URL: https://github.com/llvm/llvm-project/commit/fcf0f810ac4b22bda3f21048784ee114da1cb061
DIFF: https://github.com/llvm/llvm-project/commit/fcf0f810ac4b22bda3f21048784ee114da1cb061.diff

LOG: [Clang][AMDGPU] Enable `avail-extern-to-local` for ThinLTO in HIP (#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.

Added: 
    clang/test/Driver/hip-thinlto.hip

Modified: 
    clang/lib/Driver/ToolChains/HIPAMD.cpp

Removed: 
    


################################################################################
diff  --git a/clang/lib/Driver/ToolChains/HIPAMD.cpp b/clang/lib/Driver/ToolChains/HIPAMD.cpp
index 52b8a4510792f..4419339720b87 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..4227cd3f2e9f9
--- /dev/null
+++ b/clang/test/Driver/hip-thinlto.hip
@@ -0,0 +1,8 @@
+// RUN: %clang -foffload-lto=thin -nogpulib -nogpuinc %s -### 2>&1 | FileCheck %s
+
+// CHECK: -plugin-opt=thinlto
+// CHECK-SAME: -plugin-opt=-force-import-all
+// CHECK-SAME: -plugin-opt=-avail-extern-to-local
+int main(int, char *[]) {
+  return 0;
+}