[clang] AddDefaultRTL (PR #68220)
Joseph Huber via cfe-commits
cfe-commits at lists.llvm.org
Wed Oct 4 06:54:17 PDT 2023
https://github.com/jhuber6 created https://github.com/llvm/llvm-project/pull/68220
- [LinkerWrapper] Fix resolution of weak symbols during LTO
- [Libomptarget] Make the DeviceRTL configuration globals weak
>From f2e29b6136d245e0712bfb87de1f4253d12dd6f5 Mon Sep 17 00:00:00 2001
From: Joseph Huber <jhuber6 at vols.utk.edu>
Date: Wed, 4 Oct 2023 07:34:01 -0500
Subject: [PATCH 1/2] [LinkerWrapper] Fix resolution of weak symbols during LTO
Summary:
Weak symbols are supposed to have the semantics that they can be
overriden by a strong (i.e. global) definition. This wasn't being
respected by the LTO pass because we simply used the first definition
that was available. This patch fixes that logic by doing a first pass
over the symbols to check for strong resolutions that could override a
weak one.
A lot of fake linker logic is ending up in the linker wrapper. If there
were an option to handle this in `lld` it would be a lot cleaner, but
unfortunately supporting NVPTX is a big restriction as their binaries
require the `nvlink` tool.
---
.../ClangLinkerWrapper.cpp | 14 ++++++++
openmp/libomptarget/test/offloading/weak.c | 33 +++++++++++++++++++
2 files changed, 47 insertions(+)
create mode 100644 openmp/libomptarget/test/offloading/weak.c
diff --git a/clang/tools/clang-linker-wrapper/ClangLinkerWrapper.cpp b/clang/tools/clang-linker-wrapper/ClangLinkerWrapper.cpp
index 632e37e3cac8fec..f95b0f8cb317c75 100644
--- a/clang/tools/clang-linker-wrapper/ClangLinkerWrapper.cpp
+++ b/clang/tools/clang-linker-wrapper/ClangLinkerWrapper.cpp
@@ -595,6 +595,7 @@ Error linkBitcodeFiles(SmallVectorImpl<OffloadFile> &InputFiles,
StringRef Arch = Args.getLastArgValue(OPT_arch_EQ);
SmallVector<OffloadFile, 4> BitcodeInputFiles;
+ DenseSet<StringRef> StrongResolutions;
DenseSet<StringRef> UsedInRegularObj;
DenseSet<StringRef> UsedInSharedLib;
BumpPtrAllocator Alloc;
@@ -608,6 +609,18 @@ Error linkBitcodeFiles(SmallVectorImpl<OffloadFile> &InputFiles,
file_magic Type = identify_magic(Buffer.getBuffer());
switch (Type) {
case file_magic::bitcode: {
+ Expected<IRSymtabFile> IRSymtabOrErr = readIRSymtab(Buffer);
+ if (!IRSymtabOrErr)
+ return IRSymtabOrErr.takeError();
+
+ // Check for any strong resolutions we need to preserve.
+ for (unsigned I = 0; I != IRSymtabOrErr->Mods.size(); ++I) {
+ for (const auto &Sym : IRSymtabOrErr->TheReader.module_symbols(I)) {
+ if (!Sym.isFormatSpecific() && Sym.isGlobal() && !Sym.isWeak() &&
+ !Sym.isUndefined())
+ StrongResolutions.insert(Saver.save(Sym.Name));
+ }
+ }
BitcodeInputFiles.emplace_back(std::move(File));
continue;
}
@@ -696,6 +709,7 @@ Error linkBitcodeFiles(SmallVectorImpl<OffloadFile> &InputFiles,
// it is undefined or another definition has already been used.
Res.Prevailing =
!Sym.isUndefined() &&
+ !(Sym.isWeak() && StrongResolutions.contains(Sym.getName())) &&
PrevailingSymbols.insert(Saver.save(Sym.getName())).second;
// We need LTO to preseve the following global symbols:
diff --git a/openmp/libomptarget/test/offloading/weak.c b/openmp/libomptarget/test/offloading/weak.c
new file mode 100644
index 000000000000000..ca81db958356b2e
--- /dev/null
+++ b/openmp/libomptarget/test/offloading/weak.c
@@ -0,0 +1,33 @@
+// RUN: %libomptarget-compile-generic -DA -c -o %t-a.o
+// RUN: %libomptarget-compile-generic -DB -c -o %t-b.o
+// RUN: %libomptarget-compile-generic %t-a.o %t-b.o && \
+// RUN: %libomptarget-run-generic | %fcheck-generic
+
+#if defined(A)
+__attribute__((weak)) int x = 999;
+#pragma omp declare target to(x)
+#elif defined(B)
+int x = 42;
+#pragma omp declare target to(x)
+__attribute__((weak)) int y = 42;
+#pragma omp declare target to(y)
+#else
+
+#include <stdio.h>
+
+extern int x;
+#pragma omp declare target to(x)
+extern int y;
+#pragma omp declare target to(y)
+
+int main() {
+ x = 0;
+
+#pragma omp target update from(x)
+#pragma omp target update from(y)
+
+ // CHECK: PASS
+ if (x == 42 && y == 42)
+ printf("PASS\n");
+}
+#endif
>From ed9cb56c91b3ed6e51fd9f2cb5381cd5b4101fb2 Mon Sep 17 00:00:00 2001
From: Joseph Huber <jhuber6 at vols.utk.edu>
Date: Wed, 4 Oct 2023 08:47:43 -0500
Subject: [PATCH 2/2] [Libomptarget] Make the DeviceRTL configuration globals
weak
Summary:
This patch applies weak linkage to the config globals by the name
`__omp_rtl...`. This is because when passing `-nogpulib` we will not
link in or create these globals. This allows the OpenMP device RTL to be
self contained without requiring the additional definitions from the
`clang` compiler. In the standard case, this should not affect the
current behavior, this is because the strong defintiion coming from the
compiler should always override the weak definition we default to here.
In the case that these are not defined by the compiler, these will
remain weak. This will impact optimizations somewhat, but the previous
behaviour was that it would not link so that is an improvement.
Depends on: https://github.com/llvm/llvm-project/pull/68215
---
openmp/libomptarget/DeviceRTL/src/Configuration.cpp | 8 ++++----
openmp/libomptarget/DeviceRTL/src/exports | 4 ++++
2 files changed, 8 insertions(+), 4 deletions(-)
diff --git a/openmp/libomptarget/DeviceRTL/src/Configuration.cpp b/openmp/libomptarget/DeviceRTL/src/Configuration.cpp
index 5deee9c53926e77..809c5f03886b048 100644
--- a/openmp/libomptarget/DeviceRTL/src/Configuration.cpp
+++ b/openmp/libomptarget/DeviceRTL/src/Configuration.cpp
@@ -20,10 +20,10 @@ using namespace ompx;
#pragma omp begin declare target device_type(nohost)
-// defined by CGOpenMPRuntimeGPU
-extern uint32_t __omp_rtl_debug_kind;
-extern uint32_t __omp_rtl_assume_no_thread_state;
-extern uint32_t __omp_rtl_assume_no_nested_parallelism;
+// Weak definitions will be overridden by CGOpenmpRuntimeGPU if enabled.
+[[gnu::weak]] extern const uint32_t __omp_rtl_debug_kind = 0;
+[[gnu::weak]] extern const uint32_t __omp_rtl_assume_no_thread_state = 0;
+[[gnu::weak]] extern const uint32_t __omp_rtl_assume_no_nested_parallelism = 0;
// This variable should be visibile to the plugin so we override the default
// hidden visibility.
diff --git a/openmp/libomptarget/DeviceRTL/src/exports b/openmp/libomptarget/DeviceRTL/src/exports
index 2d13195aa7dc87c..fbcda3ce8f555ca 100644
--- a/openmp/libomptarget/DeviceRTL/src/exports
+++ b/openmp/libomptarget/DeviceRTL/src/exports
@@ -3,6 +3,10 @@ ompx_*
*llvm_*
__kmpc_*
+__omp_rtl_debug_kind
+__omp_rtl_assume_no_thread_state
+__omp_rtl_assume_no_nested_parallelism
+
_ZN4ompx*
IsSPMDMode
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