[libcxx-commits] [clang] [libcxx] [clang] Fix -Wuninitialized for values passed by const pointers (PR #147221)

[Igor Kudrin via libcxx-commits]

https://github.com/igorkudrin updated https://github.com/llvm/llvm-project/pull/147221

>From f1e26fed6c5023ba59990112ec4a77b024247e4b Mon Sep 17 00:00:00 2001
From: Igor Kudrin <ikudrin at accesssoftek.com>
Date: Fri, 4 Jul 2025 23:55:41 -0700
Subject: [PATCH 1/2] [clang] Fix -Wuninitialized for values passed by const
 pointers

This enables producing a "variable is uninitialized" warning when a
value is passed to a pointer-to-const argument:

```
void foo(const int *);
void test() {
  int *v;
  foo(v);
}
```

Fixes #37460
---
 clang/lib/Analysis/UninitializedValues.cpp | 13 +++++--------
 clang/test/SemaCXX/uninitialized.cpp       |  8 ++++++--
 2 files changed, 11 insertions(+), 10 deletions(-)

diff --git a/clang/lib/Analysis/UninitializedValues.cpp b/clang/lib/Analysis/UninitializedValues.cpp
index b2a68b6c39a7e..540838f89f20c 100644
--- a/clang/lib/Analysis/UninitializedValues.cpp
+++ b/clang/lib/Analysis/UninitializedValues.cpp
@@ -438,13 +438,10 @@ void ClassifyRefs::VisitCallExpr(CallExpr *CE) {
     return;
   }
   bool isTrivialBody = hasTrivialBody(CE);
-  // If a value is passed by const pointer to a function,
-  // we should not assume that it is initialized by the call, and we
-  // conservatively do not assume that it is used.
-  // If a value is passed by const reference to a function,
-  // it should already be initialized.
-  for (CallExpr::arg_iterator I = CE->arg_begin(), E = CE->arg_end();
-       I != E; ++I) {
+  // A value passed by const pointer or reference to a function should already
+  // be initialized.
+  for (CallExpr::arg_iterator I = CE->arg_begin(), E = CE->arg_end(); I != E;
+       ++I) {
     if ((*I)->isGLValue()) {
       if ((*I)->getType().isConstQualified())
         classify((*I), isTrivialBody ? Ignore : ConstRefUse);
@@ -453,7 +450,7 @@ void ClassifyRefs::VisitCallExpr(CallExpr *CE) {
       const auto *UO = dyn_cast<UnaryOperator>(Ex);
       if (UO && UO->getOpcode() == UO_AddrOf)
         Ex = UO->getSubExpr();
-      classify(Ex, Ignore);
+      classify(Ex, Use);
     }
   }
 }
diff --git a/clang/test/SemaCXX/uninitialized.cpp b/clang/test/SemaCXX/uninitialized.cpp
index c7b987e2172e6..4a944ba830bc3 100644
--- a/clang/test/SemaCXX/uninitialized.cpp
+++ b/clang/test/SemaCXX/uninitialized.cpp
@@ -162,12 +162,16 @@ void test_const_ptr() {
   int a;
   int b;  // expected-note {{initialize the variable 'b' to silence this warning}}
   foo(&a);
-  bar(&b);
-  b = a + b; // expected-warning {{variable 'b' is uninitialized when used here}}
+  bar(&b); // expected-warning {{variable 'b' is uninitialized when used here}}
+  b = a + b;
   int *ptr;  //expected-note {{initialize the variable 'ptr' to silence this warning}}
   const int *ptr2;
   foo(ptr); // expected-warning {{variable 'ptr' is uninitialized when used here}}
   foobar(&ptr2);
+  int *ptr3; // expected-note {{initialize the variable 'ptr3' to silence this warning}}
+  const int *ptr4; // expected-note {{initialize the variable 'ptr4' to silence this warning}}
+  bar(ptr3); // expected-warning {{variable 'ptr3' is uninitialized when used here}}
+  bar(ptr4); // expected-warning {{variable 'ptr4' is uninitialized when used here}}
 }
 }
 

>From d63b5dc783cfb9388515c3c9e7a736005e289b34 Mon Sep 17 00:00:00 2001
From: Igor Kudrin <ikudrin at accesssoftek.com>
Date: Sun, 6 Jul 2025 18:41:48 -0700
Subject: [PATCH 2/2] fixup! libcxx tests

---
 .../ostream.inserters.arithmetic/pointer.pass.cpp             | 4 ++--
 .../ostream.inserters.arithmetic/pointer.volatile.pass.cpp    | 4 ++--
 2 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/libcxx/test/std/input.output/iostream.format/output.streams/ostream.formatted/ostream.inserters.arithmetic/pointer.pass.cpp b/libcxx/test/std/input.output/iostream.format/output.streams/ostream.formatted/ostream.inserters.arithmetic/pointer.pass.cpp
index 61fd0a804ecd3..f15f1b96b4b27 100644
--- a/libcxx/test/std/input.output/iostream.format/output.streams/ostream.formatted/ostream.inserters.arithmetic/pointer.pass.cpp
+++ b/libcxx/test/std/input.output/iostream.format/output.streams/ostream.formatted/ostream.inserters.arithmetic/pointer.pass.cpp
@@ -62,14 +62,14 @@ int main(int, char**)
     {
         testbuf<char> sb1;
         std::ostream os1(&sb1);
-        int n1;
+        int n1 = 0;
         os1 << &n1;
         assert(os1.good());
         std::string s1(sb1.str());
 
         testbuf<char> sb2;
         std::ostream os2(&sb2);
-        int n2;
+        int n2 = 0;
         os2 << &n2;
         assert(os2.good());
         std::string s2(sb2.str());
diff --git a/libcxx/test/std/input.output/iostream.format/output.streams/ostream.formatted/ostream.inserters.arithmetic/pointer.volatile.pass.cpp b/libcxx/test/std/input.output/iostream.format/output.streams/ostream.formatted/ostream.inserters.arithmetic/pointer.volatile.pass.cpp
index 69d84f640d54e..6a1cde15a69bd 100644
--- a/libcxx/test/std/input.output/iostream.format/output.streams/ostream.formatted/ostream.inserters.arithmetic/pointer.volatile.pass.cpp
+++ b/libcxx/test/std/input.output/iostream.format/output.streams/ostream.formatted/ostream.inserters.arithmetic/pointer.volatile.pass.cpp
@@ -61,7 +61,7 @@ class testbuf : public std::basic_streambuf<CharT> {
 int main(int, char**) {
   testbuf<char> sb1;
   std::ostream os1(&sb1);
-  int n1;
+  int n1 = 0;
   os1 << &n1;
   assert(os1.good());
   std::string s1 = sb1.str();
@@ -74,7 +74,7 @@ int main(int, char**) {
 
   testbuf<char> sb3;
   std::ostream os3(&sb3);
-  volatile int n3;
+  volatile int n3 = 0;
   os3 << &n3;
   assert(os3.good());
   std::string s3 = sb3.str();