[Clang] Initialize AtLeastAsSpecialized to prevent undefined behavior in Sema::isTemplateTemplateParameterAtLeastAsSpecializedAs()

[smanna12]

This patch fixes a static analyzer bug where the boolean variable AtLeastAsSpecialized was used uninitialized. The variable is now explicitly initialized to false before its potential modification within a lambda function to ensure that it always holds a valid value when returned, preventing undefined behavior due to uninitialized variable usage in Sema::isTemplateTemplateParameterAtLeastAsSpecializedAs().

[llvmbot]

@llvm/pr-subscribers-clang

Author: None (smanna12)

Changes

… in Sema::isTemplateTemplateParameterAtLeastAsSpecializedAs()

This patch fixes a static analyzer bug where the boolean variable AtLeastAsSpecialized was used uninitialized. The variable is now explicitly initialized to false before its potential modification within a lambda function to ensure that it always holds a valid value when returned, preventing undefined behavior due to uninitialized variable usage in Sema::isTemplateTemplateParameterAtLeastAsSpecializedAs().

---

Full diff: https://github.com/llvm/llvm-project/pull/95195.diff

1 Files Affected:

• (modified) clang/lib/Sema/SemaTemplateDeduction.cpp (+1-1)

diff --git a/clang/lib/Sema/SemaTemplateDeduction.cpp b/clang/lib/Sema/SemaTemplateDeduction.cpp
index befeb38e1fe5b..df0d6908d0a78 100644
--- a/clang/lib/Sema/SemaTemplateDeduction.cpp
+++ b/clang/lib/Sema/SemaTemplateDeduction.cpp
@@ -6447,7 +6447,7 @@ bool Sema::isTemplateTemplateParameterAtLeastAsSpecializedAs(
   if (Inst.isInvalid())
     return false;
 
-  bool AtLeastAsSpecialized;
+  bool AtLeastAsSpecialized = false;
   runWithSufficientStackSpace(Info.getLocation(), [&] {
     AtLeastAsSpecialized =
         ::FinishTemplateArgumentDeduction(

[mizvekov]

There is no potential UB, this is a false positive: this lambda will always be executed before runWithSufficientStackSpace returns.

[mizvekov]

runWithSufficientStackSpace is a small helper used to prevent stack exhaustion.

[cor3ntin]

as @mizvekov said, there is no UB here.
A better improvement would be to let runWithSufficientStackSpace return a value, so we can write

bool AtLeastAsSpecialized =  runWithSufficientStackSpace(/*...*/);