[Clang][AST] Fix crash in APValue::LValueBase::getType when we have invalid decl

[shafik]

In some cases when calling APValue::LValueBase::getType() when we have a ValueDecl in some cases we don't handle invalid decls. We iterating over redeclarations we reset the current decl to the current most recent decl and we check the next redeclaration to ensure it is not invalid.

Fixes: #69468

[llvmbot]

@llvm/pr-subscribers-clang

Author: Shafik Yaghmour (shafik)

Changes

In some cases when calling APValue::LValueBase::getType() when we have a ValueDecl in some cases we don't handle invalid decls. We iterating over redeclarations we reset the current decl to the current most recent decl and we check the next redeclaration to ensure it is not invalid.

Fixes: #69468

---

Full diff: https://github.com/llvm/llvm-project/pull/75130.diff

2 Files Affected:

• (modified) clang/lib/AST/APValue.cpp (+3-1)
• (added) clang/test/AST/gh69468.cpp (+14)

diff --git a/clang/lib/AST/APValue.cpp b/clang/lib/AST/APValue.cpp
index 4eae308ef5b34..2ccd83a1d4823 100644
--- a/clang/lib/AST/APValue.cpp
+++ b/clang/lib/AST/APValue.cpp
@@ -70,11 +70,13 @@ QualType APValue::LValueBase::getType() const {
     // constexpr int *p = &arr[1]; // valid?
     //
     // For now, we take the most complete type we can find.
-    for (auto *Redecl = cast<ValueDecl>(D->getMostRecentDecl()); Redecl;
+    for (auto *Redecl = cast<ValueDecl>(D->getMostRecentDecl());
+         Redecl && !Redecl->isInvalidDecl();
          Redecl = cast_or_null<ValueDecl>(Redecl->getPreviousDecl())) {
       QualType T = Redecl->getType();
       if (!T->isIncompleteArrayType())
         return T;
+      D = Redecl;
     }
     return D->getType();
   }
diff --git a/clang/test/AST/gh69468.cpp b/clang/test/AST/gh69468.cpp
new file mode 100644
index 0000000000000..8c93fa5e828ac
--- /dev/null
+++ b/clang/test/AST/gh69468.cpp
@@ -0,0 +1,14 @@
+// RUN: %clang_cc1 -verify %s
+
+
+a[i] = b[i]; // expected-error {{use of undeclared identifier 'i'}} \
+             // expected-error {{a type specifier is required for all declarations}} \
+	     // expected-error {{use of undeclared identifier 'b'}} \
+	     // expected-error {{use of undeclared identifier 'i'}}
+extern char b[];
+extern char a[];
+
+void foo(int j) {
+  // This used to crash here
+  a[j] = b[j];
+}

[erichkeane]

This doesn't seem right to me... this change makes us skip the 'right' answer when there is a redecl in the way.

In reality, I wonder if this whole loop is misguided. If we want to just find the 'last' non-incomplete-array-type, that search is pretty easy by looping through 'redecls'. I THINK this ends up better as:

QualType T = D->getMostRecentDecl()->getType();
for (const auto *R : D->redecls()) { // unsure if this needs to be 'getMostRecentDecl?'
  if (!R->isInvalidDecl() && !R->getType()->isIncompleteArrayType())
    T = R->getType();
}
return T;

redecl_iterator is a forward-iterator, else I'd suggest just doing an rbegin/rend type thing on them.

[shafik]

We are dealing with ill-formed code here. So there is not "right answer", right? Are you saying that we might misdiagnose an error?

Or are you saying the original code is incorrect and you think there is well-formed code we will not do the correct thing on?

[erichkeane]

The problem is that if the 'invalid' decl is the last one, we end up giving up on this loop entirely. If the purpose here is to just skip an invalid decl, we probably need to skip JUST it, not all previous ones too.