CodeGen, IR: Add target-{cpu,features} attributes to functions created via createWithDefaultAttr().

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 llvm#93633.

Reviewers: fmayer, MaskRay, eugenis

Reviewed By: MaskRay

Pull Request: llvm#96721

Author: pcc

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,

clang/test/CodeGen/asan-frame-pointer.cpp

@@ -8,12 +8,12 @@ int global;
 
 // NONE: define internal void @asan.module_ctor() #[[#ATTR:]] {
 // NONE: define internal void @asan.module_dtor() #[[#ATTR]] {
-// NONE: attributes #[[#ATTR]] = { nounwind }
+// NONE: attributes #[[#ATTR]] = { nounwind
 
 // NONLEAF: define internal void @asan.module_ctor() #[[#ATTR:]] {
 // NONLEAF: define internal void @asan.module_dtor() #[[#ATTR]] {
-// NONLEAF: attributes #[[#ATTR]] = { nounwind "frame-pointer"="non-leaf" }
+// NONLEAF: attributes #[[#ATTR]] = { nounwind "frame-pointer"="non-leaf"
 
 // ALL: define internal void @asan.module_ctor() #[[#ATTR:]] {
 // ALL: define internal void @asan.module_dtor() #[[#ATTR]] {
-// ALL: attributes #[[#ATTR]] = { nounwind "frame-pointer"="all" }
+// ALL: attributes #[[#ATTR]] = { nounwind "frame-pointer"="all"

clang/test/CodeGen/asan-globals.cpp

@@ -67,13 +67,13 @@ void func() {
 // CHECK-NEXT: call void @__asan_unregister_globals
 // CHECK-NEXT: ret void
 
-// CHECK: attributes #[[#ATTR]] = { nounwind }
+// CHECK: attributes #[[#ATTR]] = { nounwind
 
 /// If -fasynchronous-unwind-tables, set the module flag "uwtable". ctor/dtor
 /// will thus get the uwtable attribute.
 // RUN: %clang_cc1 -emit-llvm -fsanitize=address -funwind-tables=2 -o - %s | FileCheck %s --check-prefixes=UWTABLE
 // UWTABLE: define internal void @asan.module_dtor() #[[#ATTR:]] {
-// UWTABLE: attributes #[[#ATTR]] = { nounwind uwtable }
+// UWTABLE: attributes #[[#ATTR]] = { nounwind uwtable
 // UWTABLE: ![[#]] = !{i32 7, !"uwtable", i32 2}
 
 // IGNORELIST-SRC:     @{{.*}}extra_global{{.*}} ={{.*}} global

clang/test/CodeGen/coverage-target-attr.c

@@ -0,0 +1,17 @@
+// RUN: %clang_cc1 -emit-llvm -coverage-notes-file=test.gcno -coverage-data-file=test.gcda -triple aarch64-linux-android30 -target-cpu generic -target-feature +tagged-globals -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"="+tagged-globals"
+// CHECK: attributes [[ATTR2]] = {{.*}} "target-cpu"="generic" "target-features"="+tagged-globals"
+
+__attribute__((weak)) int foo = 0;
+
+__attribute__((weak)) void bar() {}
+
+int main() {
+  if (foo) bar();
+}

clang/test/CodeGen/sanitize-metadata-nosanitize.c

@@ -93,7 +93,7 @@ __attribute__((no_sanitize("all"))) int test_no_sanitize_all(int *x, int *y) {
 // CHECK: attributes #1 = { mustprogress nofree norecurse nounwind willreturn memory(write, argmem: readwrite, inaccessiblemem: none) "min-legal-vector-width"="0" "no-trapping-math"="true" "stack-protector-buffer-size"="8" "target-features"="+cx8,+mmx,+sse,+sse2,+x87" }
 // CHECK: attributes #2 = { disable_sanitizer_instrumentation mustprogress nofree norecurse nounwind willreturn memory(write, argmem: readwrite, inaccessiblemem: none) "min-legal-vector-width"="0" "no-trapping-math"="true" "stack-protector-buffer-size"="8" "target-features"="+cx8,+mmx,+sse,+sse2,+x87" }
 // CHECK: attributes #3 = { mustprogress nofree norecurse nounwind willreturn memory(write, argmem: readwrite, inaccessiblemem: none) "min-legal-vector-width"="0" "no-trapping-math"="true" "no_sanitize_thread" "stack-protector-buffer-size"="8" "target-features"="+cx8,+mmx,+sse,+sse2,+x87" }
-// CHECK: attributes #4 = { nounwind }
+// CHECK: attributes #4 = { nounwind "target-features"="+cx8,+mmx,+sse,+sse2,+x87" }
 //.
 // CHECK: !2 = !{!"sanmd_covered!C", !3}
 // CHECK: !3 = !{i64 0}

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 = "",

llvm/include/llvm/IR/LLVMContext.h

@@ -327,6 +327,22 @@ class LLVMContext {
   [[deprecated("Always returns false")]]
   bool supportsTypedPointers() const;
 
+  /// Get or set 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();
+  void setDefaultTargetCPU(StringRef CPU);
+
+  /// Similar to {get,set}DefaultTargetCPU() but for default target-features.
+  StringRef getDefaultTargetFeatures();
+  void setDefaultTargetFeatures(StringRef Features);
+
 private:
   // Module needs access to the add/removeModule methods.
   friend class Module;

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;
 }

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;
+}

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