[llvm] [coro] Fix crash due to DILabel in `LineTableOnly` mode (PR #148095)

[Adrian Vogelsgesang via llvm-commits]

https://github.com/vogelsgesang updated https://github.com/llvm/llvm-project/pull/148095

>From bc96976c770634c0ae412a8a80eebe9243bd8cba Mon Sep 17 00:00:00 2001
From: Adrian Vogelsgesang <avogelsgesang at salesforce.com>
Date: Fri, 11 Jul 2025 01:11:53 +0000
Subject: [PATCH 1/2] [coro] Fix crash due to DILabel in `LineTableOnly` mode

Since the recent commit de3c8410d8, the `CoroSplit` pass adds `DILabel`s
to help find the location of a suspension point from its suspension
point id. Those labels are added in both `DebugEmissionKind::FullDebug`
and `DebugEmissionKind::LineTableOnly` mode. The idea was that this
information is necessary to reconstruct async stack traces and should
hence also be available for LineTableOnly.

Unfortunately, it turns out that the DWARF backend does not expect to
find any DILabel debug metadata if the emission kind is set to
LineTableOnly. The Dwarf backend simply runs into an assertion in that
case.

This commit fixes the issue by only adding `DILabel` for FullDebug.
---
 llvm/lib/Transforms/Coroutines/CoroSplit.cpp | 9 +++------
 1 file changed, 3 insertions(+), 6 deletions(-)

diff --git a/llvm/lib/Transforms/Coroutines/CoroSplit.cpp b/llvm/lib/Transforms/Coroutines/CoroSplit.cpp
index 077dbe697a87e..f1e17ff01a4a2 100644
--- a/llvm/lib/Transforms/Coroutines/CoroSplit.cpp
+++ b/llvm/lib/Transforms/Coroutines/CoroSplit.cpp
@@ -1484,12 +1484,9 @@ struct SwitchCoroutineSplitter {
     // If there is no DISubprogram for F, it implies the function is compiled
     // without debug info. So we also don't generate debug info for the
     // suspension points.
-    bool AddDebugLabels =
-        (DIS && DIS->getUnit() &&
-         (DIS->getUnit()->getEmissionKind() ==
-              DICompileUnit::DebugEmissionKind::FullDebug ||
-          DIS->getUnit()->getEmissionKind() ==
-              DICompileUnit::DebugEmissionKind::LineTablesOnly));
+    bool AddDebugLabels = DIS && DIS->getUnit() &&
+                          (DIS->getUnit()->getEmissionKind() ==
+                           DICompileUnit::DebugEmissionKind::FullDebug);
 
     // resume.entry:
     //  %index.addr = getelementptr inbounds %f.Frame, %f.Frame* %FramePtr, i32

>From 03b4ce38ee0b123b21c6c72cfc34b53e19b756a0 Mon Sep 17 00:00:00 2001
From: Adrian Vogelsgesang <avogelsgesang at salesforce.com>
Date: Fri, 11 Jul 2025 20:56:15 +0000
Subject: [PATCH 2/2] Add test case

---
 .../Coroutines/coro-split-dbg-labels.ll           | 15 +++++++++++++--
 1 file changed, 13 insertions(+), 2 deletions(-)

diff --git a/llvm/test/Transforms/Coroutines/coro-split-dbg-labels.ll b/llvm/test/Transforms/Coroutines/coro-split-dbg-labels.ll
index 63f59a19e1c93..511e1e66b706d 100644
--- a/llvm/test/Transforms/Coroutines/coro-split-dbg-labels.ll
+++ b/llvm/test/Transforms/Coroutines/coro-split-dbg-labels.ll
@@ -1,14 +1,19 @@
 ; Tests that we add DILabels for the suspend points.
 ;
-; We check both the generated LLVM:
+; Check the generated LLVM:
 ; RUN: opt < %s -passes='cgscc(coro-split)' -S | FileCheck %s
 ;
-; And the debug info:
+; Check the generated DWARF debug info:
 ; REQUIRES: object-emission
 ; RUN: opt < %s -passes='cgscc(coro-split),coro-cleanup' \
 ; RUN:   | %llc_dwarf -O0 -filetype=obj -o - \
 ; RUN:   | llvm-dwarfdump - \
 ; RUN:   | FileCheck %s -check-prefix=DWARF
+;
+; Check that we don't emit any DILabel if in `LineTablesOnly` mode
+; RUN: sed -e 's/emissionKind: FullDebug/emissionKind: LineTablesOnly/' %s \
+; RUN:   | opt -passes='cgscc(coro-split)' -S \
+; RUN:   | FileCheck %s -check-prefix=LINE-TABLE
 
 source_filename = "coro.c"
 
@@ -83,6 +88,12 @@ coro_Suspend:                                     ; preds = %for.cond, %if.then,
 ; CHECK: ![[DESTROY_0]] = !DILabel(scope: !{{[0-9]+}}, name: "__coro_resume_0", file: !{{[0-9]*}}, line: 12, column: 6, isArtificial: true, coroSuspendIdx: 0)
 ; CHECK: ![[DESTROY_1]] = !DILabel(scope: !{{[0-9]+}}, name: "__coro_resume_1", file: !{{[0-9]*}}, line: 14, column: 6, isArtificial: true, coroSuspendIdx: 1)
 
+; Check the we do not emit any DILabels in LineTableOnly mode.
+; The DWARF emitter cannot handle this and would run into an assertion
+; LINE-TABLE: !DICompileUnit{{.*}}LineTablesOnly
+; LINE-TABLE-NOT: DILabel
+
+
 ; DWARF:        {{.*}}DW_TAG_label
 ; DWARF-NEXT:    DW_AT_name ("__coro_resume_0")
 ; DWARF-NEXT:    DW_AT_decl_file