[clang] [-Wunsafe-buffer-usage] Ignore consteval functions (PR #171503)

[via cfe-commits]

https://github.com/mxms0 updated https://github.com/llvm/llvm-project/pull/171503

>From 6ca667130537476bd4268e15b0f899446f30b6e8 Mon Sep 17 00:00:00 2001
From: mxms <mxms at google.com>
Date: Tue, 9 Dec 2025 20:54:14 +0000
Subject: [PATCH 1/3] [-Wunsafe-buffer-usage] Ignore consteval functions

We dont need to visit or warn on consteval functions as they can't have UB.
---
 clang/lib/Analysis/UnsafeBufferUsage.cpp        | 5 +++++
 clang/test/SemaCXX/warn-unsafe-buffer-usage.cpp | 7 +++++++
 2 files changed, 12 insertions(+)

diff --git a/clang/lib/Analysis/UnsafeBufferUsage.cpp b/clang/lib/Analysis/UnsafeBufferUsage.cpp
index da155d31d4a88..893462e3bad58 100644
--- a/clang/lib/Analysis/UnsafeBufferUsage.cpp
+++ b/clang/lib/Analysis/UnsafeBufferUsage.cpp
@@ -4458,6 +4458,11 @@ void clang::checkUnsafeBufferUsage(const Decl *D,
   SmallVector<Stmt *> Stmts;
 
   if (const auto *FD = dyn_cast<FunctionDecl>(D)) {
+    // Consteval functions are free of UB by the spec, so we don't need to
+    // visit them or produce diagnostics.
+    if (FD->isConsteval()) {
+      return;
+    }
     // We do not want to visit a Lambda expression defined inside a method
     // independently. Instead, it should be visited along with the outer method.
     // FIXME: do we want to do the same thing for `BlockDecl`s?
diff --git a/clang/test/SemaCXX/warn-unsafe-buffer-usage.cpp b/clang/test/SemaCXX/warn-unsafe-buffer-usage.cpp
index 41d38ada48788..6fad7585026f2 100644
--- a/clang/test/SemaCXX/warn-unsafe-buffer-usage.cpp
+++ b/clang/test/SemaCXX/warn-unsafe-buffer-usage.cpp
@@ -406,4 +406,11 @@ void testMultiLineDeclStmt(int * p) {
   foo(ap1[1]);  // expected-note{{used in buffer access here}}
 }
 
+#if __cplusplus >= 202002L
+consteval void testConstevalPtrArithmetic(int idx) {
+  int y[3] = {0, 1, 2};
+  foo(y[idx]);
+}
+#endif
+
 #endif

>From 1e47613d844ded927ccd6f2c6c2831fd615f7d8f Mon Sep 17 00:00:00 2001
From: mxms <mxms at google.com>
Date: Tue, 9 Dec 2025 20:54:14 +0000
Subject: [PATCH 2/3] [-Wunsafe-buffer-usage] Ignore consteval functions

We dont need to visit or warn on consteval functions as they can't have UB.
---
 clang/lib/Analysis/UnsafeBufferUsage.cpp | 4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

diff --git a/clang/lib/Analysis/UnsafeBufferUsage.cpp b/clang/lib/Analysis/UnsafeBufferUsage.cpp
index 893462e3bad58..23798becf36a0 100644
--- a/clang/lib/Analysis/UnsafeBufferUsage.cpp
+++ b/clang/lib/Analysis/UnsafeBufferUsage.cpp
@@ -4460,9 +4460,7 @@ void clang::checkUnsafeBufferUsage(const Decl *D,
   if (const auto *FD = dyn_cast<FunctionDecl>(D)) {
     // Consteval functions are free of UB by the spec, so we don't need to
     // visit them or produce diagnostics.
-    if (FD->isConsteval()) {
-      return;
-    }
+    if (FD->isConsteval()) return;
     // We do not want to visit a Lambda expression defined inside a method
     // independently. Instead, it should be visited along with the outer method.
     // FIXME: do we want to do the same thing for `BlockDecl`s?

>From c76782929442d3bf74a777654a2675a6958bea03 Mon Sep 17 00:00:00 2001
From: mxms <mxms at google.com>
Date: Thu, 11 Dec 2025 01:50:49 +0000
Subject: [PATCH 3/3] Fix formatting

---
 clang/lib/Analysis/UnsafeBufferUsage.cpp | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/clang/lib/Analysis/UnsafeBufferUsage.cpp b/clang/lib/Analysis/UnsafeBufferUsage.cpp
index 23798becf36a0..99c7a44174b3a 100644
--- a/clang/lib/Analysis/UnsafeBufferUsage.cpp
+++ b/clang/lib/Analysis/UnsafeBufferUsage.cpp
@@ -4460,7 +4460,8 @@ void clang::checkUnsafeBufferUsage(const Decl *D,
   if (const auto *FD = dyn_cast<FunctionDecl>(D)) {
     // Consteval functions are free of UB by the spec, so we don't need to
     // visit them or produce diagnostics.
-    if (FD->isConsteval()) return;
+    if (FD->isConsteval())
+      return;
     // We do not want to visit a Lambda expression defined inside a method
     // independently. Instead, it should be visited along with the outer method.
     // FIXME: do we want to do the same thing for `BlockDecl`s?