[llvm] [MC] Avoid DWARF emission after inline asm errors (PR #228707)

[Mathew Joseph via llvm-commits]

https://github.com/mathew1046 created https://github.com/llvm/llvm-project/pull/228707

## Summary

This prevents an assertion during DWARF finalization after an inline assembly error.

## Reproducer

```llvm
define void @f() {
  call void asm sideeffect ".file 3 \22b\22", ""()
  ret void
}
```

The inline assembly contains:

```asm
.file 3 "b"
```

without defining file numbers 1 and 2 first.

With an assertions-enabled LLVM build, `llc -filetype=obj` reports the expected `unassigned file number` diagnostics and then aborts with:

```text
Assertion `!MCDwarfFiles[i].Name.empty()` failed.
```

The failure occurs because inline assembly is parsed with `NoFinalize=true`. `AsmParser::Run()` reports the error through its local error state, but the error was not propagated to `MCContext`. Later, `MCStreamer::finish()` continued into `MCObjectStreamer::finishImpl()`, which attempted to emit a DWARF line table containing empty file-table entries.

## Fix

Propagate deferred inline assembly errors to `MCContext` and stop streamer finalization when the context has an error. This preserves the existing `unassigned file number` diagnostics and prevents incomplete DWARF emission.

## Testing

Added `llvm/test/CodeGen/X86/inline-asm-file-directive-error.ll`.

Validated with an assertions-enabled LLVM build:

```bash
ninja -C /home/mathew/llvm-project-build-assertions llc
/home/mathew/llvm-project-build-assertions/bin/llc -mtriple=x86_64-unknown-linux-gnu -filetype=obj llvm/test/CodeGen/X86/inline-asm-file-directive-error.ll -o /dev/null
```

The test now reports the original errors and exits nonzero without asserting. The same behavior was also checked with `-dwarf-version=5`, and valid inline assembly continues to compile successfully.

Fixes #228061

>From ffe8080d7602c6cdbcaf7f8d22aa25097cb29cdb Mon Sep 17 00:00:00 2001
From: Mathew Joseph <mathewjosephparakka at gmail.com>
Date: Sat, 3 Oct 2026 18:18:52 +0530
Subject: [PATCH] [MC] Avoid DWARF emission after inline asm errors

Propagate deferred inline assembly errors to the MC context so streamer finalization does not emit incomplete DWARF line tables. This preserves the existing diagnostics for unassigned .file entries and prevents assertions in the DWARF file table emitter.

Fixes #228061
---
 llvm/include/llvm/MC/MCContext.h                      |  1 +
 llvm/lib/MC/MCParser/AsmParser.cpp                    |  3 +++
 llvm/lib/MC/MCStreamer.cpp                            |  3 +++
 .../CodeGen/X86/inline-asm-file-directive-error.ll    | 11 +++++++++++
 4 files changed, 18 insertions(+)
 create mode 100644 llvm/test/CodeGen/X86/inline-asm-file-directive-error.ll

diff --git a/llvm/include/llvm/MC/MCContext.h b/llvm/include/llvm/MC/MCContext.h
index 7e76abe08f56f7..c392b82104e72a 100644
--- a/llvm/include/llvm/MC/MCContext.h
+++ b/llvm/include/llvm/MC/MCContext.h
@@ -838,6 +838,7 @@ class MCContext {
   }
 
   bool hadError() { return HadError; }
+  void setHadError() { HadError = true; }
   LLVM_ABI void diagnose(const SMDiagnostic &SMD);
   LLVM_ABI void reportError(SMLoc L, const Twine &Msg);
   LLVM_ABI void reportWarning(SMLoc L, const Twine &Msg);
diff --git a/llvm/lib/MC/MCParser/AsmParser.cpp b/llvm/lib/MC/MCParser/AsmParser.cpp
index 588cc8e3ffde3f..f067e4d81761fe 100644
--- a/llvm/lib/MC/MCParser/AsmParser.cpp
+++ b/llvm/lib/MC/MCParser/AsmParser.cpp
@@ -1073,6 +1073,9 @@ bool AsmParser::Run(bool NoInitialTextSection, bool NoFinalize) {
     Out.finish(Lexer.getLoc());
   }
 
+  if (HadError && NoFinalize)
+    getContext().setHadError();
+
   return HadError || getContext().hadError();
 }
 
diff --git a/llvm/lib/MC/MCStreamer.cpp b/llvm/lib/MC/MCStreamer.cpp
index 1d51fbc46a43c4..e4f77bc484edb8 100644
--- a/llvm/lib/MC/MCStreamer.cpp
+++ b/llvm/lib/MC/MCStreamer.cpp
@@ -1299,6 +1299,9 @@ void MCStreamer::emitWindowsUnwindTables() {}
 void MCStreamer::emitWindowsUnwindTables(WinEH::FrameInfo *Frame) {}
 
 void MCStreamer::finish(SMLoc EndLoc) {
+  if (getContext().hadError())
+    return;
+
   if (hasUnfinishedDwarfFrameInfo() ||
       (!WinFrameInfos.empty() && !WinFrameInfos.back()->End)) {
     getContext().reportError(EndLoc, "Unfinished frame!");
diff --git a/llvm/test/CodeGen/X86/inline-asm-file-directive-error.ll b/llvm/test/CodeGen/X86/inline-asm-file-directive-error.ll
new file mode 100644
index 00000000000000..ed1d5b26950873
--- /dev/null
+++ b/llvm/test/CodeGen/X86/inline-asm-file-directive-error.ll
@@ -0,0 +1,11 @@
+; RUN: not llc -mtriple=x86_64-unknown-linux-gnu -filetype=obj %s -o %t.o 2>&1 | FileCheck %s
+
+; An inline assembly error must prevent deferred DWARF finalization.
+define void @f() {
+  call void asm sideeffect ".file 3 \22b\22", ""()
+  ret void
+}
+
+; CHECK: error: unassigned file number: 1 for .file directives
+; CHECK: error: unassigned file number: 2 for .file directives
+; CHECK-NOT: Assertion
\ No newline at end of file