[clang][-Wunsafe-buffer-usage] Ignore consteval functions

[mxms0]

We dont need to visit or warn on consteval functions as they can't have UB.

[mxms0]

cc @jkorous-apple

[llvmbot]

@llvm/pr-subscribers-clang-analysis

@llvm/pr-subscribers-clang

Author: Max (mxms0)

Changes

We dont need to visit or warn on consteval functions as they can't have UB.

---

Full diff: https://github.com/llvm/llvm-project/pull/171503.diff

2 Files Affected:

• (modified) clang/lib/Analysis/UnsafeBufferUsage.cpp (+5)
• (modified) clang/test/SemaCXX/warn-unsafe-buffer-usage.cpp (+7)

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

[github-actions]

🐧 Linux x64 Test Results

• 112066 tests passed
• 4571 tests skipped

✅ The build succeeded and all tests passed.

[github-actions]

🪟 Windows x64 Test Results

• 53087 tests passed
• 2185 tests skipped

✅ The build succeeded and all tests passed.

[github-actions]

✅ With the latest revision this PR passed the C/C++ code formatter.

[fmayer]

nit: add [clang] to the description?

[mxms0]

nit: add [clang] to the description?

Done :)