Windows: Disable LLVM crash dialog boxes.

compiler/rustc_codegen_llvm/src/llvm/ffi.rs

@@ -987,6 +987,7 @@ pub type SelfProfileAfterPassCallback = unsafe extern "C" fn(*mut c_void);
 
 extern "C" {
     pub fn LLVMRustInstallFatalErrorHandler();
+    pub fn LLVMRustDisableSystemDialogsOnCrash();
 
     // Create and destroy contexts.
     pub fn LLVMRustContextCreate(shouldDiscardNames: bool) -> &'static mut Context;

compiler/rustc_codegen_llvm/src/llvm_util.rs

@@ -46,6 +46,12 @@ unsafe fn configure_llvm(sess: &Session) {
     let mut llvm_args = Vec::with_capacity(n_args + 1);
 
     llvm::LLVMRustInstallFatalErrorHandler();
+    // On Windows, an LLVM assertion will open an Abort/Retry/Ignore dialog
+    // box for the purpose of launching a debugger. However, on CI this will
+    // cause it to hang until it times out, which can take several hours.
+    if std::env::var_os("CI").is_some() {
+        llvm::LLVMRustDisableSystemDialogsOnCrash();
+    }
 
     fn llvm_arg_to_arg_name(full_arg: &str) -> &str {
         full_arg.trim().split(|c: char| c == '=' || c.is_whitespace()).next().unwrap_or("")

compiler/rustc_llvm/llvm-wrapper/RustWrapper.cpp

@@ -76,6 +76,10 @@ extern "C" void LLVMRustInstallFatalErrorHandler() {
   install_fatal_error_handler(FatalErrorHandler);
 }
 
+extern "C" void LLVMRustDisableSystemDialogsOnCrash() {
+  sys::DisableSystemDialogsOnCrash();
+}
+
 extern "C" char *LLVMRustGetLastError(void) {
   char *Ret = LastError;
   LastError = nullptr;