[clang] Do not print locations in anonymous tag names. (PR #159592)

[via cfe-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-clang-codegen

Author: Shubham Sandeep Rastogi (rastogishubham)

<details>
<summary>Changes</summary>

If we use LTO as a driver, we can see that even if we have lambdas in
template parameters, two debug entries from different CUs will get
merged in LTO, but their human-readable DW_AT_name will be different if
we emit the locations in anonymous tag names.

Therefore we would never have two dies with the same linkage name but
different human readable names. Which probably should not happen.

This change prevents that from happening.

In our example:

We can see with `AnonymousTagLocations` set to true, the dwarfdump output will 
be

`DW_AT_name     ("Foo&lt;(lambda at a.cpp:12:5){}&gt;")`

But with `AnonymousTagLocations` set to true, the dwarfdump output will be

`DW_AT_name     ("Foo&lt;(lambda){}&gt;")`


---
Full diff: https://github.com/llvm/llvm-project/pull/159592.diff


2 Files Affected:

- (modified) clang/lib/CodeGen/CGDebugInfo.cpp (+2) 
- (added) clang/test/DebugInfo/CXX/anonymous-locs.cpp (+14) 


``````````diff
diff --git a/clang/lib/CodeGen/CGDebugInfo.cpp 
b/clang/lib/CodeGen/CGDebugInfo.cpp
index 578d09f7971d6..9df792be1f283 100644
--- a/clang/lib/CodeGen/CGDebugInfo.cpp
+++ b/clang/lib/CodeGen/CGDebugInfo.cpp
@@ -397,6 +397,8 @@ PrintingPolicy CGDebugInfo::getPrintingPolicy() const {
 
   // Apply -fdebug-prefix-map.
   PP.Callbacks = &PrintCB;
+  // Disable printing of location of an anonymous tag name.
+  PP.AnonymousTagLocations = false;
   return PP;
 }
 
diff --git a/clang/test/DebugInfo/CXX/anonymous-locs.cpp 
b/clang/test/DebugInfo/CXX/anonymous-locs.cpp
new file mode 100644
index 0000000000000..48a8aff57d520
--- /dev/null
+++ b/clang/test/DebugInfo/CXX/anonymous-locs.cpp
@@ -0,0 +1,14 @@
+// RUN: %clang_cc1 -std=c++20 -emit-obj -debug-info-kind=standalone 
-dwarf-version=5 -triple x86_64-apple-darwin -o %t %s 
+// RUN: llvm-dwarfdump %t | FileCheck %s
+
+// CHECK: DW_TAG_structure_type
+// CHECK-NEXT: DW_AT_calling_convention        (DW_CC_pass_by_value)
+// CHECK-NEXT: DW_AT_name      ("Foo<(lambda){}>")
+
+template<auto T>
+struct Foo {
+};
+
+Foo<[] {}> f;
+
+auto func() { return f; }
\ No newline at end of file

``````````

</details>


https://github.com/llvm/llvm-project/pull/159592
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