Make some "safe" llvm ops actually sound

Author: oli-obk

compiler/rustc_codegen_llvm/src/back/write.rs

@@ -1182,7 +1182,7 @@ fn create_msvc_imps(
         .filter_map(|val| {
             // Exclude some symbols that we know are not Rust symbols.
             let name = llvm::get_value_name(val);
-            if ignored(name) { None } else { Some((val, name)) }
+            if ignored(&name) { None } else { Some((val, name)) }
         })
         .map(move |(val, name)| {
             let mut imp_name = prefix.as_bytes().to_vec();

compiler/rustc_codegen_llvm/src/builder/autodiff.rs

@@ -306,7 +306,7 @@ fn generate_enzyme_call<'ll>(
     // add outer_fn name to ad_name to make it unique, in case users apply autodiff to multiple
     // functions. Unwrap will only panic, if LLVM gave us an invalid string.
     let name = llvm::get_value_name(outer_fn);
-    let outer_fn_name = std::str::from_utf8(name).unwrap();
+    let outer_fn_name = std::str::from_utf8(&name).unwrap();
     ad_name.push_str(outer_fn_name);
 
     // Let us assume the user wrote the following function square:

compiler/rustc_codegen_llvm/src/consts.rs

@@ -430,7 +430,7 @@ impl<'ll> CodegenCx<'ll, '_> {
                 // specific rules on what can be cast. So instead of adding a new way to
                 // generate static initializers that match the static's type, we picked
                 // the easier option and retroactively change the type of the static item itself.
-                let name = llvm::get_value_name(g).to_vec();
+                let name = llvm::get_value_name(g);
                 llvm::set_value_name(g, b"");
 
                 let linkage = llvm::get_linkage(g);

compiler/rustc_codegen_llvm/src/llvm/mod.rs

@@ -211,7 +211,7 @@ pub(crate) fn SetFunctionCallConv(fn_: &Value, cc: CallConv) {
 // function.
 // For more details on COMDAT sections see e.g., https://www.airs.com/blog/archives/52
 pub(crate) fn SetUniqueComdat(llmod: &Module, val: &Value) {
-    let name_buf = get_value_name(val).to_vec();
+    let name_buf = get_value_name(val);
     let name =
         CString::from_vec_with_nul(name_buf).or_else(|buf| CString::new(buf.into_bytes())).unwrap();
     set_comdat(llmod, val, &name);
@@ -319,12 +319,14 @@ pub(crate) fn get_param(llfn: &Value, index: c_uint) -> &Value {
     }
 }
 
-/// Safe wrapper for `LLVMGetValueName2` into a byte slice
-pub(crate) fn get_value_name(value: &Value) -> &[u8] {
+/// Safe wrapper for `LLVMGetValueName2`
+/// Needs to allocate the value, because `set_value_name` will invalidate
+/// the pointer.
+pub(crate) fn get_value_name(value: &Value) -> Vec<u8> {
     unsafe {
         let mut len = 0;
         let data = LLVMGetValueName2(value, &mut len);
-        std::slice::from_raw_parts(data.cast(), len)
+        std::slice::from_raw_parts(data.cast(), len).to_vec()
     }
 }