Improve inline asm error diagnostics

1 files changed, 43 insertions, 8 deletions

diff --git a/src/librustc_codegen_llvm/back/write.rs b/src/librustc_codegen_llvm/back/write.rs
index 57e018bba6a..02a9294930d 100644
--- a/src/librustc_codegen_llvm/back/write.rs
+++ b/src/librustc_codegen_llvm/back/write.rs
@@ -23,6 +23,7 @@ use rustc_middle::bug;
 use rustc_middle::ty::TyCtxt;
 use rustc_session::config::{self, Lto, OutputType, Passes, Sanitizer, SwitchWithOptPath};
 use rustc_session::Session;
+use rustc_span::InnerSpan;
 use rustc_target::spec::{CodeModel, RelocModel};
 
 use libc::{c_char, c_int, c_uint, c_void, size_t};
@@ -238,12 +239,19 @@ impl<'a> Drop for DiagnosticHandlers<'a> {
     }
 }
 
-unsafe extern "C" fn report_inline_asm(
+fn report_inline_asm(
     cgcx: &CodegenContext<LlvmCodegenBackend>,
-    msg: &str,
-    cookie: c_uint,
+    msg: String,
+    mut cookie: c_uint,
+    source: Option<(String, Vec<InnerSpan>)>,
 ) {
-    cgcx.diag_emitter.inline_asm_error(cookie as u32, msg.to_owned());
+    // In LTO build we may get srcloc values from other crates which are invalid
+    // since they use a different source map. To be safe we just suppress these
+    // in LTO builds.
+    if matches!(cgcx.lto, Lto::Fat | Lto::Thin) {
+        cookie = 0;
+    }
+    cgcx.diag_emitter.inline_asm_error(cookie as u32, msg, source);
 }
 
 unsafe extern "C" fn inline_asm_handler(diag: &SMDiagnostic, user: *const c_void, cookie: c_uint) {
@@ -252,10 +260,37 @@ unsafe extern "C" fn inline_asm_handler(diag: &SMDiagnostic, user: *const c_void
     }
     let (cgcx, _) = *(user as *const (&CodegenContext<LlvmCodegenBackend>, &Handler));
 
-    let msg = llvm::build_string(|s| llvm::LLVMRustWriteSMDiagnosticToString(diag, s))
-        .expect("non-UTF8 SMDiagnostic");
+    // Recover the post-substitution assembly code from LLVM for better
+    // diagnostics.
+    let mut have_source = false;
+    let mut buffer = String::new();
+    let mut loc = 0;
+    let mut ranges = [0; 8];
+    let mut num_ranges = ranges.len() / 2;
+    let msg = llvm::build_string(|msg| {
+        buffer = llvm::build_string(|buffer| {
+            have_source = llvm::LLVMRustUnpackSMDiagnostic(
+                diag,
+                msg,
+                buffer,
+                &mut loc,
+                ranges.as_mut_ptr(),
+                &mut num_ranges,
+            );
+        })
+        .expect("non-UTF8 inline asm");
+    })
+    .expect("non-UTF8 SMDiagnostic");
+
+    let source = have_source.then(|| {
+        let mut spans = vec![InnerSpan::new(loc as usize, loc as usize)];
+        for i in 0..num_ranges {
+            spans.push(InnerSpan::new(ranges[i * 2] as usize, ranges[i * 2 + 1] as usize));
+        }
+        (buffer, spans)
+    });
 
-    report_inline_asm(cgcx, &msg, cookie);
+    report_inline_asm(cgcx, msg, cookie, source);
 }
 
 unsafe extern "C" fn diagnostic_handler(info: &DiagnosticInfo, user: *mut c_void) {
@@ -266,7 +301,7 @@ unsafe extern "C" fn diagnostic_handler(info: &DiagnosticInfo, user: *mut c_void
 
     match llvm::diagnostic::Diagnostic::unpack(info) {
         llvm::diagnostic::InlineAsm(inline) => {
-            report_inline_asm(cgcx, &llvm::twine_to_string(inline.message), inline.cookie);
+            report_inline_asm(cgcx, llvm::twine_to_string(inline.message), inline.cookie, None);
         }
 
         llvm::diagnostic::Optimization(opt) => {