adding proper error handling for offload

Author: ZuseZ4

compiler/rustc_codegen_llvm/messages.ftl

@@ -18,8 +18,13 @@ codegen_llvm_lto_bitcode_from_rlib = failed to get bitcode from object file for
 codegen_llvm_mismatch_data_layout =
     data-layout for target `{$rustc_target}`, `{$rustc_layout}`, differs from LLVM target's `{$llvm_target}` default layout, `{$llvm_layout}`
 
-codegen_llvm_offload_without_enable = using the offload feature requires -Z offload=Enable
+codegen_llvm_offload_without_enable = using the offload feature requires -Z offload=<Device or Host=/absolute/path/to/host.out>
+codegen_llvm_offload_no_abs_path = using the `-Z offload=Host=/absolute/path/to/host.out` flag requires an absolute path
+codegen_llvm_offload_nonexisting = the given path/file to `host.out` does not exist. Did you forget to run the device compilation first?
+codegen_llvm_offload_no_host_out = using the `-Z offload=Host=/absolute/path/to/host.out` flag must point to a `host.out` file
 codegen_llvm_offload_without_fat_lto = using the offload feature requires -C lto=fat
+codegen_llvm_offload_bundleimages_failed = BundleImages call failed, `host.out` was not created
+codegen_llvm_offload_embed_failed = EmbedBufferInModule call failed, `host.o` was not created
 
 codegen_llvm_parse_bitcode = failed to parse bitcode for LTO module
 codegen_llvm_parse_bitcode_with_llvm_err = failed to parse bitcode for LTO module: {$llvm_err}

compiler/rustc_codegen_llvm/src/back/write.rs

@@ -783,9 +783,8 @@ pub(crate) unsafe fn llvm_optimize(
                 module.module_llvm.tm.raw(),
                 device_out_c.as_ptr(),
             );
-            assert!(ok, "LLVMRustBundleImages (device -> host.out) failed");
-            if !device_out.exists() {
-                panic!("BundleImages failed, `host.out` was not created!");
+            if !ok || !device_out.exists() {
+                dcx.emit_err(crate::errors::OffloadBundleImagesFailed);
             }
         }
     }
@@ -803,15 +802,16 @@ pub(crate) unsafe fn llvm_optimize(
         {
             let device_pathbuf = PathBuf::from(device_path);
             if device_pathbuf.is_relative() {
-                panic!("Absolute path is needed");
+                dcx.emit_err(crate::errors::OffloadWithoutAbsPath);
             } else if device_pathbuf
                 .file_name()
                 .and_then(|n| n.to_str())
                 .is_some_and(|n| n != "host.out")
             {
-                panic!("Need path to the host.out file");
+                dcx.emit_err(crate::errors::OffloadWrongFileName);
+            } else if !device_pathbuf.exists() {
+                dcx.emit_err(crate::errors::OffloadNonexistingPath);
             }
-            assert!(device_pathbuf.exists());
             let host_path = cgcx.output_filenames.path(OutputType::Object);
             let host_dir = host_path.parent().unwrap();
             let out_obj = host_dir.join("host.o");
@@ -823,7 +823,9 @@ pub(crate) unsafe fn llvm_optimize(
             let llmod2 = llvm::LLVMCloneModule(module.module_llvm.llmod());
             let ok =
                 unsafe { llvm::LLVMRustOffloadEmbedBufferInModule(llmod2, host_out_c.as_ptr()) };
-            assert!(ok, "LLVMRustOffloadEmbedBufferInModule failed");
+            if !ok {
+                dcx.emit_err(crate::errors::OffloadEmbedFailed);
+            }
             write_output_file(
                 dcx,
                 module.module_llvm.tm.raw(),
@@ -835,10 +837,6 @@ pub(crate) unsafe fn llvm_optimize(
                 &cgcx.prof,
                 true,
             );
-            if !out_obj.exists() {
-                dbg!("{:?} does not exist!", out_obj);
-                panic!("FinalizeOffload failed!");
-            }
             // We ignore cgcx.save_temps here and unconditionally always keep our `host.out` artifact.
             // Otherwise, recompiling the host code would fail since we deleted that device artifact
             // in the previous host compilation, which would be confusing at best.

compiler/rustc_codegen_llvm/src/errors.rs

@@ -48,6 +48,26 @@ pub(crate) struct OffloadWithoutEnable;
 #[diag(codegen_llvm_offload_without_fat_lto)]
 pub(crate) struct OffloadWithoutFatLTO;
 
+#[derive(Diagnostic)]
+#[diag(codegen_llvm_offload_no_abs_path)]
+pub(crate) struct OffloadWithoutAbsPath;
+
+#[derive(Diagnostic)]
+#[diag(codegen_llvm_offload_no_host_out)]
+pub(crate) struct OffloadWrongFileName;
+
+#[derive(Diagnostic)]
+#[diag(codegen_llvm_offload_nonexisting)]
+pub(crate) struct OffloadNonexistingPath;
+
+#[derive(Diagnostic)]
+#[diag(codegen_llvm_offload_bundleimages_failed)]
+pub(crate) struct OffloadBundleImagesFailed;
+
+#[derive(Diagnostic)]
+#[diag(codegen_llvm_offload_embed_failed)]
+pub(crate) struct OffloadEmbedFailed;
+
 #[derive(Diagnostic)]
 #[diag(codegen_llvm_lto_bitcode_from_rlib)]
 pub(crate) struct LtoBitcodeFromRlib {