[clang] [clang][Coverage] Fix crash for nested macro in system headers (PR #181319)

[via cfe-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-clang-codegen

Author: None (Nuullll)

<details>
<summary>Changes</summary>

When compiling with coverage enabled, clang crashes if a file includes a system header that contains nested macro expansions.

The existing logic in `CoverageMappingBuilder::gatherFileIDs` attempts to remap locations from system macros by checking `SM.isInSystemMacro(Loc)`. This check is insufficient as it misses cases where a location's *spelling location* is still in a system header, such as with nested macros. This leads to the `!SM.isInSystemHeader(SM.getSpellingLoc(Loc))` assertion firing later on.

This patch fixes #<!-- -->179316 by checking the spelling location anyway. It replaces the assertion with a check that skips any region whose spelling location is in a system header (when system header coverage is disabled). This correctly handles all cases, including nested macros.

---
Full diff: https://github.com/llvm/llvm-project/pull/181319.diff


3 Files Affected:

- (modified) clang/lib/CodeGen/CoverageMappingGen.cpp (+8-2) 
- (added) clang/test/CoverageMapping/Inputs/nested.h (+2) 
- (added) clang/test/CoverageMapping/system_nested_macro.cpp (+8) 


``````````diff
diff --git a/clang/lib/CodeGen/CoverageMappingGen.cpp b/clang/lib/CodeGen/CoverageMappingGen.cpp
index 803037d1874b3..82426d2893484 100644
--- a/clang/lib/CodeGen/CoverageMappingGen.cpp
+++ b/clang/lib/CodeGen/CoverageMappingGen.cpp
@@ -401,8 +401,14 @@ class CoverageMappingBuilder {
       if (!Visited.insert(File).second)
         continue;
 
-      assert(SystemHeadersCoverage ||
-             !SM.isInSystemHeader(SM.getSpellingLoc(Loc)));
+      // Ignore regions from system headers unless collecting coverage from
+      // system headers is explicitly enabled.
+      if (!SystemHeadersCoverage &&
+          SM.isInSystemHeader(SM.getSpellingLoc(Loc))) {
+        assert(!Region.isMCDCBranch() && !Region.isMCDCDecision() &&
+               "Don't suppress the condition in system headers");
+        continue;
+      }
 
       unsigned Depth = 0;
       for (SourceLocation Parent = getIncludeOrExpansionLoc(Loc);
diff --git a/clang/test/CoverageMapping/Inputs/nested.h b/clang/test/CoverageMapping/Inputs/nested.h
new file mode 100644
index 0000000000000..46c46242e1f73
--- /dev/null
+++ b/clang/test/CoverageMapping/Inputs/nested.h
@@ -0,0 +1,2 @@
+#define Y X
+Y
diff --git a/clang/test/CoverageMapping/system_nested_macro.cpp b/clang/test/CoverageMapping/system_nested_macro.cpp
new file mode 100644
index 0000000000000..ec73d2a69de5f
--- /dev/null
+++ b/clang/test/CoverageMapping/system_nested_macro.cpp
@@ -0,0 +1,8 @@
+// clang previously crashes when including nested macro from a system header.
+// REQUIRES: asserts
+// RUN: %clang -isystem %S/Inputs -fprofile-instr-generate -fcoverage-mapping -c %s
+
+int main() {
+#define X ;
+#include <nested.h>
+}

``````````

</details>


https://github.com/llvm/llvm-project/pull/181319