Auto merge of #96285 - flip1995:pk-vfe, r=nagisa

Introduce `-Zvirtual-function-elimination` codegen flag

Fixes #68262

This PR adds a codegen flag `-Zvirtual-function-elimination` to enable the VFE optimization in LLVM. To make this work, additonal  information has to be added to vtables ([`!vcall_visibility` metadata](https://llvm.org/docs/TypeMetadata.html#vcall-visibility-metadata) and a `typeid` of the trait). Furthermore, instead of just `load`ing functions, the [`llvm.type.checked.load` intrinsic](https://llvm.org/docs/LangRef.html#llvm-type-checked-load-intrinsic) has to be used to map functions to vtables.

For technical details of the changes, see the commit messages.

I also tested this flag on https://github.com/tock/tock on different boards to verify that this fixes the issue https://github.com/tock/tock/issues/2594. This flag is able to improve the size of the resulting binary by about 8k-9k bytes by removing the unused debug print functions.

[Rendered documentation update](https://github.com/flip1995/rust/blob/pk-vfe/src/doc/rustc/src/codegen-options/index.md#virtual-function-elimination)

1 files changed, 10 insertions, 0 deletions

diff --git a/compiler/rustc_llvm/llvm-wrapper/RustWrapper.cpp b/compiler/rustc_llvm/llvm-wrapper/RustWrapper.cpp
index f90bb7f2368..a52d5340242 100644
--- a/compiler/rustc_llvm/llvm-wrapper/RustWrapper.cpp
+++ b/compiler/rustc_llvm/llvm-wrapper/RustWrapper.cpp
@@ -672,10 +672,20 @@ extern "C" void LLVMRustAddModuleFlag(
   unwrap(M)->addModuleFlag(MergeBehavior, Name, Value);
 }
 
+extern "C" bool LLVMRustHasModuleFlag(LLVMModuleRef M, const char *Name,
+                                      size_t Len) {
+  return unwrap(M)->getModuleFlag(StringRef(Name, Len)) != nullptr;
+}
+
 extern "C" LLVMValueRef LLVMRustMetadataAsValue(LLVMContextRef C, LLVMMetadataRef MD) {
   return wrap(MetadataAsValue::get(*unwrap(C), unwrap(MD)));
 }
 
+extern "C" void LLVMRustGlobalAddMetadata(
+    LLVMValueRef Global, unsigned Kind, LLVMMetadataRef MD) {
+  unwrap<GlobalObject>(Global)->addMetadata(Kind, *unwrap<MDNode>(MD));
+}
+
 extern "C" LLVMRustDIBuilderRef LLVMRustDIBuilderCreate(LLVMModuleRef M) {
   return new DIBuilder(*unwrap(M));
 }