release/21.x: [Analysis] Prevent revisiting block when searching for noreturn vars (#150582)

[llvmbot]

Backport 330b40e

Requested by: @pawosm-arm

[llvmbot]

@erichkeane What do you think about merging this PR to the release branch?

[llvmbot]

@llvm/pr-subscribers-clang

Author: None (llvmbot)

Changes

Backport 330b40e

Requested by: @pawosm-arm

---

Full diff: https://github.com/llvm/llvm-project/pull/151381.diff

2 Files Affected:

• (modified) clang/lib/Sema/AnalysisBasedWarnings.cpp (+4)
• (added) clang/test/SemaCXX/noreturn-weverything.c (+15)

diff --git a/clang/lib/Sema/AnalysisBasedWarnings.cpp b/clang/lib/Sema/AnalysisBasedWarnings.cpp
index 5e75c64eb2b9a..85ac3c06ec2c2 100644
--- a/clang/lib/Sema/AnalysisBasedWarnings.cpp
+++ b/clang/lib/Sema/AnalysisBasedWarnings.cpp
@@ -503,8 +503,12 @@ static bool areAllValuesNoReturn(const VarDecl *VD, const CFGBlock &VarBlk,
 
   TransferFunctions TF(VD);
   BackwardDataflowWorklist Worklist(*AC.getCFG(), AC);
+  llvm::DenseSet<const CFGBlock *> Visited;
   Worklist.enqueueBlock(&VarBlk);
   while (const CFGBlock *B = Worklist.dequeue()) {
+    if (Visited.contains(B))
+      continue;
+    Visited.insert(B);
     // First check the current block.
     for (CFGBlock::const_reverse_iterator ri = B->rbegin(), re = B->rend();
          ri != re; ++ri) {
diff --git a/clang/test/SemaCXX/noreturn-weverything.c b/clang/test/SemaCXX/noreturn-weverything.c
new file mode 100644
index 0000000000000..92a587d395639
--- /dev/null
+++ b/clang/test/SemaCXX/noreturn-weverything.c
@@ -0,0 +1,15 @@
+// RUN: %clang_cc1 -fsyntax-only %s -Weverything
+
+void free(void *);
+typedef void (*set_free_func)(void *);
+struct Method {
+  int nparams;
+  int *param;
+};
+void selelem_free_method(struct Method* method, void* data) {
+    set_free_func free_func = 0;
+    for (int i = 0; i < method->nparams; ++i)
+        free(&method->param[i]);
+    if (data && free_func)
+        free_func(data);
+}

[erichkeane]

Yeah, we should merge this, the multiple-visits causes no-turn analysis to infinite loop in some cases, which is obviously not great.

[pawosm-arm]

@tstellar what needs to be done to make it merged?

[github-actions]

@pawosm-arm (or anyone else). If you would like to add a note about this fix in the release notes (completely optional). Please reply to this comment with a one or two sentence description of the fix. When you are done, please add the release:note label to this PR.