[llvm] f1dad0b - [DWARFLinker] Handle empty sequences when processing `DW_AT_LLVM_stmt_sequence` attributes (#132875)

[via llvm-commits]

Author: alx32
Date: 2025-03-26T17:04:27-07:00
New Revision: f1dad0bcb58f2b8bf0d847d4a65909b797be4fa1

URL: https://github.com/llvm/llvm-project/commit/f1dad0bcb58f2b8bf0d847d4a65909b797be4fa1
DIFF: https://github.com/llvm/llvm-project/commit/f1dad0bcb58f2b8bf0d847d4a65909b797be4fa1.diff

LOG: [DWARFLinker] Handle empty sequences when processing `DW_AT_LLVM_stmt_sequence` attributes (#132875)

We previously assumed that every `DW_AT_LLVM_stmt_sequence` attribute
has a corresponding sequence in the processed line table. However, this
isn't always true. Some sequences can be removed by the linker if they
are empty, as shown
[here](https://github.com/alx32/llvm-project/blob/release/14.x/llvm/lib/DebugInfo/DWARF/DWARFDebugLine.cpp#L565-L566).
When an attribute refers to one of these removed sequences, there is no
actual sequence for it to match. In such cases, we update the attribute
to indicate that it is invalid and does not point to any sequence. This
informs readers that the attribute should be ignored.

The newly modified test would have triggered the assert that is being
removed in this patch.

Added: 
    

Modified: 
    llvm/lib/DWARFLinker/Classic/DWARFLinker.cpp
    llvm/test/tools/dsymutil/ARM/stmt-seq-macho.test
    llvm/test/tools/dsymutil/Inputs/private/tmp/stmt_seq/stmt_seq_macho.exe
    llvm/test/tools/dsymutil/Inputs/private/tmp/stmt_seq/stmt_seq_macho.o

Removed: 
    


################################################################################
diff  --git a/llvm/lib/DWARFLinker/Classic/DWARFLinker.cpp b/llvm/lib/DWARFLinker/Classic/DWARFLinker.cpp
index f66773ad2e694..ae4cc6d85c120 100644
--- a/llvm/lib/DWARFLinker/Classic/DWARFLinker.cpp
+++ b/llvm/lib/DWARFLinker/Classic/DWARFLinker.cpp
@@ -2311,8 +2311,13 @@ void DWARFLinker::DIECloner::generateLineTableForUnit(CompileUnit &Unit) {
           uint64_t OrigStmtSeq = StmtSeq.get();
           // 1. Get the original row index from the stmt list offset.
           auto OrigRowIter = SeqOffToOrigRow.find(OrigStmtSeq);
-          assert(OrigRowIter != SeqOffToOrigRow.end() &&
-                 "Stmt list offset not found in sequence offsets map");
+          // Check whether we have an output sequence for the StmtSeq offset.
+          // Some sequences are discarded by the DWARFLinker if they are invalid
+          // (empty).
+          if (OrigRowIter == SeqOffToOrigRow.end()) {
+            StmtSeq.set(UINT64_MAX);
+            continue;
+          }
           size_t OrigRowIndex = OrigRowIter->second;
 
           // 2. Get the new row index from the original row index.

diff  --git a/llvm/test/tools/dsymutil/ARM/stmt-seq-macho.test b/llvm/test/tools/dsymutil/ARM/stmt-seq-macho.test
index b5093ba767894..1dd1f61f1f7fb 100644
--- a/llvm/test/tools/dsymutil/ARM/stmt-seq-macho.test
+++ b/llvm/test/tools/dsymutil/ARM/stmt-seq-macho.test
@@ -41,12 +41,21 @@ ATTRIB int function2_copy2(int a) {
     int result = a - 22;
     return result;
 }
+
+struct logic_error {
+    logic_error(const char* s) {}
+};
+ 
+struct length_error : public logic_error {
+    __attribute__((noinline)) explicit length_error(const char* s) : logic_error(s) {}
+};
  
 int main() {
     int sum = 0;
     sum += function2_copy2(3);
     sum += function3_copy2(41);
     sum += function2_copy1(11);
+    length_error e("test");
     return sum;
 }
 EOF

diff  --git a/llvm/test/tools/dsymutil/Inputs/private/tmp/stmt_seq/stmt_seq_macho.exe b/llvm/test/tools/dsymutil/Inputs/private/tmp/stmt_seq/stmt_seq_macho.exe
index 138c418aa37b2..4dd4ee8deb0b4 100755
Binary files a/llvm/test/tools/dsymutil/Inputs/private/tmp/stmt_seq/stmt_seq_macho.exe and b/llvm/test/tools/dsymutil/Inputs/private/tmp/stmt_seq/stmt_seq_macho.exe 
diff er

diff  --git a/llvm/test/tools/dsymutil/Inputs/private/tmp/stmt_seq/stmt_seq_macho.o b/llvm/test/tools/dsymutil/Inputs/private/tmp/stmt_seq/stmt_seq_macho.o
index 0da06940a023c..76fba6580055b 100644
Binary files a/llvm/test/tools/dsymutil/Inputs/private/tmp/stmt_seq/stmt_seq_macho.o and b/llvm/test/tools/dsymutil/Inputs/private/tmp/stmt_seq/stmt_seq_macho.o 
diff er