llvmbot wrote:
<!--LLVM PR SUMMARY COMMENT-->
@llvm/pr-subscribers-llvm-ir
Author: None (pcc)
<details>
<summary>Changes</summary>
Functions created with createWithDefaultAttr() need to have the
correct target-{cpu,features} attributes to avoid miscompilations
such as using the wrong relocation type to access globals (missing
tagged-globals feature), clobbering registers specified via -ffixed-*
(missing reserve-* feature), and so on.
There's already a number of attributes copied from the module flags
onto functions created by createWithDefaultAttr(). I don't think
module flags are the right choice for the target attributes because
we don't need the conflict resolution logic between modules with
different target attributes, nor does it seem sensible to add it:
there's no unambiguously "correct" set of target attributes when
merging two modules with different attributes, and nor should there
be; it's perfectly valid for two modules to be compiled with different
target attributes, that's the whole reason why they are per-function.
This also implies that it's unnecessary to serialize the attributes in
bitcode, which implies that they shouldn't be stored on the module. We
can also observe that for the most part, createWithDefaultAttr()
is called from compiler passes such as sanitizers, coverage and
profiling passes that are part of the compile time pipeline, not
the LTO pipeline. This hints at a solution: we need to store the
attributes in a non-serialized location associated with the ambient
compilation context. Therefore in this patch I elected to store the
attributes on the LLVMContext.
There are calls to createWithDefaultAttr() in the NVPTX and AMDGPU
backends, and those calls would happen at LTO time. For those callers,
the bug still potentially exists and it would be necessary to refactor
them to create the functions at compile time if this issue is relevant
on those platforms.
Fixes #<!-- -->93633.
---
Full diff: https://github.com/llvm/llvm-project/pull/96721.diff
7 Files Affected:
- (modified) clang/lib/CodeGen/CodeGenAction.cpp (+6)
- (added) clang/test/CodeGen/coverage-target-attr.c (+17)
- (modified) llvm/include/llvm/IR/Function.h (+5-1)
- (modified) llvm/include/llvm/IR/LLVMContext.h (+20)
- (modified) llvm/lib/IR/Function.cpp (+6)
- (modified) llvm/lib/IR/LLVMContext.cpp (+16)
- (modified) llvm/lib/IR/LLVMContextImpl.h (+3)
``````````diff
diff --git a/clang/lib/CodeGen/CodeGenAction.cpp
b/clang/lib/CodeGen/CodeGenAction.cpp
index 6d3efdb5ffe34..7766383fdc890 100644
--- a/clang/lib/CodeGen/CodeGenAction.cpp
+++ b/clang/lib/CodeGen/CodeGenAction.cpp
@@ -299,6 +299,9 @@ void BackendConsumer::HandleTranslationUnit(ASTContext &C) {
Ctx.setDiagnosticHandler(std::make_unique<ClangDiagnosticHandler>(
CodeGenOpts, this));
+ Ctx.setDefaultTargetCPU(TargetOpts.CPU);
+ Ctx.setDefaultTargetFeatures(llvm::join(TargetOpts.Features, ","));
+
Expected<std::unique_ptr<llvm::ToolOutputFile>> OptRecordFileOrErr =
setupLLVMOptimizationRemarks(
Ctx, CodeGenOpts.OptRecordFile, CodeGenOpts.OptRecordPasses,
@@ -1205,6 +1208,9 @@ void CodeGenAction::ExecuteAction() {
Ctx.setDiagnosticHandler(
std::make_unique<ClangDiagnosticHandler>(CodeGenOpts, &Result));
+ Ctx.setDefaultTargetCPU(TargetOpts.CPU);
+ Ctx.setDefaultTargetFeatures(llvm::join(TargetOpts.Features, ","));
+
Expected<std::unique_ptr<llvm::ToolOutputFile>> OptRecordFileOrErr =
setupLLVMOptimizationRemarks(
Ctx, CodeGenOpts.OptRecordFile, CodeGenOpts.OptRecordPasses,
diff --git a/clang/test/CodeGen/coverage-target-attr.c
b/clang/test/CodeGen/coverage-target-attr.c
new file mode 100644
index 0000000000000..3929d7b43df69
--- /dev/null
+++ b/clang/test/CodeGen/coverage-target-attr.c
@@ -0,0 +1,17 @@
+// RUN: %clang -S -emit-llvm --coverage --target=aarch64-linux-android30
-fsanitize=hwaddress %s -o %t
+// RUN: FileCheck %s < %t
+
+// CHECK: define internal void @__llvm_gcov_writeout() unnamed_addr
[[ATTR:#[0-9]+]]
+// CHECK: define internal void @__llvm_gcov_reset() unnamed_addr [[ATTR]]
+// CHECK: define internal void @__llvm_gcov_init() unnamed_addr [[ATTR]]
+// CHECK: define internal void @hwasan.module_ctor() [[ATTR2:#[0-9]+]]
+// CHECK: attributes [[ATTR]] = {{.*}} "target-cpu"="generic"
"target-features"="+fix-cortex-a53-835769,+fp-armv8,+neon,+outline-atomics,+tagged-globals,+v8a"
+// CHECK: attributes [[ATTR2]] = {{.*}} "target-cpu"="generic"
"target-features"="+fix-cortex-a53-835769,+fp-armv8,+neon,+outline-atomics,+tagged-globals,+v8a"
+
+__attribute__((weak)) int foo = 0;
+
+__attribute__((weak)) void bar() {}
+
+int main() {
+ if (foo) bar();
+}
diff --git a/llvm/include/llvm/IR/Function.h b/llvm/include/llvm/IR/Function.h
index 5468cedb0815a..6bd997b7ac75a 100644
--- a/llvm/include/llvm/IR/Function.h
+++ b/llvm/include/llvm/IR/Function.h
@@ -181,10 +181,14 @@ class LLVM_EXTERNAL_VISIBILITY Function : public
GlobalObject,
const Twine &N, Module &M);
/// Creates a function with some attributes recorded in llvm.module.flags
- /// applied.
+ /// and the LLVMContext applied.
///
/// Use this when synthesizing new functions that need attributes that would
/// have been set by command line options.
+ ///
+ /// This function should not be called from backends or the LTO pipeline. If
+ /// it is called from one of those places, some default attributes will not
be
+ /// applied to the function.
static Function *createWithDefaultAttr(FunctionType *Ty, LinkageTypes
Linkage,
unsigned AddrSpace,
const Twine &N = "",
diff --git a/llvm/include/llvm/IR/LLVMContext.h
b/llvm/include/llvm/IR/LLVMContext.h
index 89ad6f1572c67..177d6e1817089 100644
--- a/llvm/include/llvm/IR/LLVMContext.h
+++ b/llvm/include/llvm/IR/LLVMContext.h
@@ -327,6 +327,26 @@ class LLVMContext {
[[deprecated("Always returns false")]]
bool supportsTypedPointers() const;
+ /// Get the current "default" target CPU (target-cpu function attribute). The
+ /// intent is that compiler frontends will set this to a value that reflects
+ /// the attribute that a function would get "by default" without any specific
+ /// function attributes, and compiler passes will attach the attribute to
+ /// newly created functions that are not associated with a particular
+ /// function, such as global initializers. Function::createWithDefaultAttr()
+ /// will create functions with this attribute. This function should only be
+ /// called by passes that run at compile time and not by the backend or LTO
+ /// passes.
+ StringRef getDefaultTargetCPU();
+
+ /// See getDefaultTargetCPU().
+ void setDefaultTargetCPU(StringRef CPU);
+
+ /// Similar to getDefaultTargetCPU() but for default target-features instead.
+ StringRef getDefaultTargetFeatures();
+
+ /// See getDefaultTargetFeatures().
+ void setDefaultTargetFeatures(StringRef Features);
+
private:
// Module needs access to the add/removeModule methods.
friend class Module;
diff --git a/llvm/lib/IR/Function.cpp b/llvm/lib/IR/Function.cpp
index 9360e6d7d274c..1190a3fb9be23 100644
--- a/llvm/lib/IR/Function.cpp
+++ b/llvm/lib/IR/Function.cpp
@@ -397,6 +397,12 @@ Function *Function::createWithDefaultAttr(FunctionType *Ty,
}
if (M->getModuleFlag("function_return_thunk_extern"))
B.addAttribute(Attribute::FnRetThunkExtern);
+ StringRef DefaultCPU = F->getContext().getDefaultTargetCPU();
+ if (!DefaultCPU.empty())
+ B.addAttribute("target-cpu", DefaultCPU);
+ StringRef DefaultFeatures = F->getContext().getDefaultTargetFeatures();
+ if (!DefaultFeatures.empty())
+ B.addAttribute("target-features", DefaultFeatures);
F->addFnAttrs(B);
return F;
}
diff --git a/llvm/lib/IR/LLVMContext.cpp b/llvm/lib/IR/LLVMContext.cpp
index 8120cccace40b..194c7e7581cfb 100644
--- a/llvm/lib/IR/LLVMContext.cpp
+++ b/llvm/lib/IR/LLVMContext.cpp
@@ -390,3 +390,19 @@ void LLVMContext::setOpaquePointers(bool Enable) const {
bool LLVMContext::supportsTypedPointers() const {
return false;
}
+
+StringRef LLVMContext::getDefaultTargetCPU() {
+ return pImpl->DefaultTargetCPU;
+}
+
+void LLVMContext::setDefaultTargetCPU(StringRef CPU) {
+ pImpl->DefaultTargetCPU = CPU;
+}
+
+StringRef LLVMContext::getDefaultTargetFeatures() {
+ return pImpl->DefaultTargetFeatures;
+}
+
+void LLVMContext::setDefaultTargetFeatures(StringRef Features) {
+ pImpl->DefaultTargetFeatures = Features;
+}
diff --git a/llvm/lib/IR/LLVMContextImpl.h b/llvm/lib/IR/LLVMContextImpl.h
index 5f8df87149f04..937a87d686175 100644
--- a/llvm/lib/IR/LLVMContextImpl.h
+++ b/llvm/lib/IR/LLVMContextImpl.h
@@ -1723,6 +1723,9 @@ class LLVMContextImpl {
}
void deleteTrailingDbgRecords(BasicBlock *B) { TrailingDbgRecords.erase(B); }
+
+ std::string DefaultTargetCPU;
+ std::string DefaultTargetFeatures;
};
} // end namespace llvm
``````````
</details>
https://github.com/llvm/llvm-project/pull/96721
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