Emit LLVM optimization remarks when enabled with -Cremark

The default diagnostic handler considers all remarks to be disabled by
default unless configured otherwise through LLVM internal flags:
`-pass-remarks`, `-pass-remarks-missed`, and `-pass-remarks-analysis`.
This behaviour makes `-Cremark` ineffective on its own.

Fix this by configuring a custom diagnostic handler that enables
optimization remarks based on the value of `-Cremark` option. With
`-Cremark=all` enabling all remarks.

compiler/rustc_codegen_llvm/src/back/write.rs

@@ -259,6 +259,7 @@ pub(crate) fn save_temp_bitcode(
 pub struct DiagnosticHandlers<'a> {
     data: *mut (&'a CodegenContext<LlvmCodegenBackend>, &'a Handler),
     llcx: &'a llvm::Context,
+    old_handler: Option<&'a llvm::DiagnosticHandler>,
 }
 
 impl<'a> DiagnosticHandlers<'a> {
@@ -267,12 +268,35 @@ impl<'a> DiagnosticHandlers<'a> {
         handler: &'a Handler,
         llcx: &'a llvm::Context,
     ) -> Self {
+        let remark_passes_all: bool;
+        let remark_passes: Vec<CString>;
+        match &cgcx.remark {
+            Passes::All => {
+                remark_passes_all = true;
+                remark_passes = Vec::new();
+            }
+            Passes::Some(passes) => {
+                remark_passes_all = false;
+                remark_passes =
+                    passes.iter().map(|name| CString::new(name.as_str()).unwrap()).collect();
+            }
+        };
+        let remark_passes: Vec<*const c_char> =
+            remark_passes.iter().map(|name: &CString| name.as_ptr()).collect();
         let data = Box::into_raw(Box::new((cgcx, handler)));
         unsafe {
+            let old_handler = llvm::LLVMRustContextGetDiagnosticHandler(llcx);
+            llvm::LLVMRustContextConfigureDiagnosticHandler(
+                llcx,
+                diagnostic_handler,
+                data.cast(),
+                remark_passes_all,
+                remark_passes.as_ptr(),
+                remark_passes.len(),
+            );
             llvm::LLVMRustSetInlineAsmDiagnosticHandler(llcx, inline_asm_handler, data.cast());
-            llvm::LLVMContextSetDiagnosticHandler(llcx, diagnostic_handler, data.cast());
+            DiagnosticHandlers { data, llcx, old_handler }
         }
-        DiagnosticHandlers { data, llcx }
     }
 }
 
@@ -281,7 +305,7 @@ impl<'a> Drop for DiagnosticHandlers<'a> {
         use std::ptr::null_mut;
         unsafe {
             llvm::LLVMRustSetInlineAsmDiagnosticHandler(self.llcx, inline_asm_handler, null_mut());
-            llvm::LLVMContextSetDiagnosticHandler(self.llcx, diagnostic_handler, null_mut());
+            llvm::LLVMRustContextSetDiagnosticHandler(self.llcx, self.old_handler);
             drop(Box::from_raw(self.data));
         }
     }

compiler/rustc_codegen_llvm/src/llvm/ffi.rs

@@ -672,8 +672,12 @@ pub struct OperandBundleDef<'a>(InvariantOpaque<'a>);
 #[repr(C)]
 pub struct Linker<'a>(InvariantOpaque<'a>);
 
-pub type DiagnosticHandler = unsafe extern "C" fn(&DiagnosticInfo, *mut c_void);
-pub type InlineAsmDiagHandler = unsafe extern "C" fn(&SMDiagnostic, *const c_void, c_uint);
+extern "C" {
+    pub type DiagnosticHandler;
+}
+
+pub type DiagnosticHandlerTy = unsafe extern "C" fn(&DiagnosticInfo, *mut c_void);
+pub type InlineAsmDiagHandlerTy = unsafe extern "C" fn(&SMDiagnostic, *const c_void, c_uint);
 
 pub mod coverageinfo {
     use super::coverage_map;
@@ -2286,12 +2290,6 @@ extern "C" {
     #[allow(improper_ctypes)]
     pub fn LLVMRustWriteTwineToString(T: &Twine, s: &RustString);
 
-    pub fn LLVMContextSetDiagnosticHandler(
-        C: &Context,
-        Handler: DiagnosticHandler,
-        DiagnosticContext: *mut c_void,
-    );
-
     #[allow(improper_ctypes)]
     pub fn LLVMRustUnpackOptimizationDiagnostic(
         DI: &'a DiagnosticInfo,
@@ -2321,7 +2319,7 @@ extern "C" {
 
     pub fn LLVMRustSetInlineAsmDiagnosticHandler(
         C: &Context,
-        H: InlineAsmDiagHandler,
+        H: InlineAsmDiagHandlerTy,
         CX: *mut c_void,
     );
 
@@ -2436,4 +2434,19 @@ extern "C" {
         mod_id: *const c_char,
         data: &ThinLTOData,
     );
+
+    pub fn LLVMRustContextGetDiagnosticHandler(Context: &Context) -> Option<&DiagnosticHandler>;
+    pub fn LLVMRustContextSetDiagnosticHandler(
+        context: &Context,
+        diagnostic_handler: Option<&DiagnosticHandler>,
+    );
+    pub fn LLVMRustContextConfigureDiagnosticHandler(
+        context: &Context,
+        diagnostic_handler_callback: DiagnosticHandlerTy,
+        diagnostic_handler_context: *mut c_void,
+        remark_all_passes: bool,
+        remark_passes: *const *const c_char,
+        remark_passes_len: usize,
+    );
+
 }