https://github.com/snarang181 updated
https://github.com/llvm/llvm-project/pull/145166
>From 359dfb1a835617a83ae13865817480e68aa67750 Mon Sep 17 00:00:00 2001
From: Samarth Narang <snar...@umass.edu>
Date: Sat, 21 Jun 2025 08:42:00 -0400
Subject: [PATCH 1/4] Suppress noreturn warning if last statement in a function
is a throw
---
clang/lib/Sema/AnalysisBasedWarnings.cpp | 45 ++++++++++++++++++++
clang/test/SemaCXX/wreturn-always-throws.cpp | 22 ++++++++++
2 files changed, 67 insertions(+)
create mode 100644 clang/test/SemaCXX/wreturn-always-throws.cpp
diff --git a/clang/lib/Sema/AnalysisBasedWarnings.cpp
b/clang/lib/Sema/AnalysisBasedWarnings.cpp
index 2a107a36e24b4..85a5d99c710d5 100644
--- a/clang/lib/Sema/AnalysisBasedWarnings.cpp
+++ b/clang/lib/Sema/AnalysisBasedWarnings.cpp
@@ -626,6 +626,31 @@ struct CheckFallThroughDiagnostics {
} // anonymous namespace
+static bool isKnownToAlwaysThrow(const FunctionDecl *FD) {
+ if (!FD->hasBody())
+ return false;
+ const Stmt *Body = FD->getBody();
+ const Stmt *OnlyStmt = nullptr;
+
+ if (const auto *Compound = dyn_cast<CompoundStmt>(Body)) {
+ if (Compound->size() != 1)
+ return false; // More than one statement, can't be known to always throw.
+ OnlyStmt = *Compound->body_begin();
+ } else {
+ OnlyStmt = Body;
+ }
+
+ // Unwrap ExprWithCleanups if necessary.
+ if (const auto *EWC = dyn_cast<ExprWithCleanups>(OnlyStmt)) {
+ OnlyStmt = EWC->getSubExpr();
+ }
+ // Check if the only statement is a throw expression.
+ if (isa<CXXThrowExpr>(OnlyStmt)) {
+ return true; // Known to always throw.
+ }
+ return false; // Not known to always throw.
+}
+
/// CheckFallThroughForBody - Check that we don't fall off the end of a
/// function that should return a value. Check that we don't fall off the end
/// of a noreturn function. We assume that functions and blocks not marked
@@ -681,6 +706,26 @@ static void CheckFallThroughForBody(Sema &S, const Decl
*D, const Stmt *Body,
if (CD.diag_FallThrough_HasNoReturn)
S.Diag(RBrace, CD.diag_FallThrough_HasNoReturn) << CD.FunKind;
} else if (!ReturnsVoid && CD.diag_FallThrough_ReturnsNonVoid) {
+ // If the final statement is a call to an always-throwing function,
+ // don't warn about the fall-through.
+ if (const auto *FD = dyn_cast<FunctionDecl>(D)) {
+ if (const auto *CS = dyn_cast<CompoundStmt>(Body)) {
+ if (!CS->body_empty()) {
+ const Stmt *LastStmt = CS->body_back();
+ // Unwrap ExprWithCleanups if necessary.
+ if (const auto *EWC = dyn_cast<ExprWithCleanups>(LastStmt)) {
+ LastStmt = EWC->getSubExpr();
+ }
+ if (const auto *CE = dyn_cast<CallExpr>(LastStmt)) {
+ if (const FunctionDecl *Callee = CE->getDirectCallee()) {
+ if (isKnownToAlwaysThrow(Callee)) {
+ return; // Don't warn about fall-through.
+ }
+ }
+ }
+ }
+ }
+ }
bool NotInAllControlPaths = FallThroughType == MaybeFallThrough;
S.Diag(RBrace, CD.diag_FallThrough_ReturnsNonVoid)
<< CD.FunKind << NotInAllControlPaths;
diff --git a/clang/test/SemaCXX/wreturn-always-throws.cpp
b/clang/test/SemaCXX/wreturn-always-throws.cpp
new file mode 100644
index 0000000000000..0bbce0f5c1871
--- /dev/null
+++ b/clang/test/SemaCXX/wreturn-always-throws.cpp
@@ -0,0 +1,22 @@
+// RUN: %clang_cc1 -fsyntax-only -fcxx-exceptions -fexceptions -Wreturn-type
-verify %s
+// expected-no-diagnostics
+
+namespace std {
+ class string {
+ public:
+ string(const char*); // constructor for runtime_error
+ };
+ class runtime_error {
+ public:
+ runtime_error(const string &);
+ };
+}
+
+void throwError(const std::string& msg) {
+ throw std::runtime_error(msg);
+}
+
+int ensureZero(const int i) {
+ if (i == 0) return 0;
+ throwError("ERROR"); // no-warning
+}
>From b14827933344a1e408164c0b4eac8fa2ee5b5304 Mon Sep 17 00:00:00 2001
From: Samarth Narang <70980689+snarang...@users.noreply.github.com>
Date: Sat, 21 Jun 2025 11:05:17 -0400
Subject: [PATCH 2/4] Update clang/lib/Sema/AnalysisBasedWarnings.cpp
Co-authored-by: Copilot <175728472+copi...@users.noreply.github.com>
---
clang/lib/Sema/AnalysisBasedWarnings.cpp | 5 ++---
1 file changed, 2 insertions(+), 3 deletions(-)
diff --git a/clang/lib/Sema/AnalysisBasedWarnings.cpp
b/clang/lib/Sema/AnalysisBasedWarnings.cpp
index 85a5d99c710d5..67e379fdd7d38 100644
--- a/clang/lib/Sema/AnalysisBasedWarnings.cpp
+++ b/clang/lib/Sema/AnalysisBasedWarnings.cpp
@@ -624,9 +624,7 @@ struct CheckFallThroughDiagnostics {
}
};
-} // anonymous namespace
-
-static bool isKnownToAlwaysThrow(const FunctionDecl *FD) {
+bool isKnownToAlwaysThrow(const FunctionDecl *FD) {
if (!FD->hasBody())
return false;
const Stmt *Body = FD->getBody();
@@ -651,6 +649,7 @@ static bool isKnownToAlwaysThrow(const FunctionDecl *FD) {
return false; // Not known to always throw.
}
+} // anonymous namespace
/// CheckFallThroughForBody - Check that we don't fall off the end of a
/// function that should return a value. Check that we don't fall off the end
/// of a noreturn function. We assume that functions and blocks not marked
>From 4340fecd20a1d45ca86d3c25e6bcf85e2af581de Mon Sep 17 00:00:00 2001
From: Samarth Narang <snar...@umass.edu>
Date: Sat, 21 Jun 2025 11:29:58 -0400
Subject: [PATCH 3/4] Handle direct throws in functions.
---
clang/lib/Sema/AnalysisBasedWarnings.cpp | 4 ++++
clang/test/SemaCXX/wreturn-always-throws.cpp | 4 ++++
2 files changed, 8 insertions(+)
diff --git a/clang/lib/Sema/AnalysisBasedWarnings.cpp
b/clang/lib/Sema/AnalysisBasedWarnings.cpp
index 67e379fdd7d38..9502669612f74 100644
--- a/clang/lib/Sema/AnalysisBasedWarnings.cpp
+++ b/clang/lib/Sema/AnalysisBasedWarnings.cpp
@@ -722,6 +722,10 @@ static void CheckFallThroughForBody(Sema &S, const Decl
*D, const Stmt *Body,
}
}
}
+ // Direct throw.
+ if (isa<CXXThrowExpr>(LastStmt)) {
+ return; // Don't warn about fall-through.
+ }
}
}
}
diff --git a/clang/test/SemaCXX/wreturn-always-throws.cpp
b/clang/test/SemaCXX/wreturn-always-throws.cpp
index 0bbce0f5c1871..5d2d2f0dffefe 100644
--- a/clang/test/SemaCXX/wreturn-always-throws.cpp
+++ b/clang/test/SemaCXX/wreturn-always-throws.cpp
@@ -20,3 +20,7 @@ int ensureZero(const int i) {
if (i == 0) return 0;
throwError("ERROR"); // no-warning
}
+
+int alwaysThrows() {
+ throw std::runtime_error("This function always throws"); // no-warning
+}
>From df23c9ad2dc7cea31dbc0d93585312a1d24684db Mon Sep 17 00:00:00 2001
From: Samarth Narang <snar...@umass.edu>
Date: Sat, 21 Jun 2025 12:34:41 -0400
Subject: [PATCH 4/4] Address review comments Add a note in the release notes
about the fix for the no-return function warning
---
clang/docs/ReleaseNotes.rst | 6 ++++
clang/lib/Sema/AnalysisBasedWarnings.cpp | 35 ++++++++++--------------
2 files changed, 21 insertions(+), 20 deletions(-)
diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index 96477ef6ddc9a..060fcc04721e8 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -642,6 +642,12 @@ Improvements to Clang's diagnostics
#GH69470, #GH59391, #GH58172, #GH46215, #GH45915, #GH45891, #GH44490,
#GH36703, #GH32903, #GH23312, #GH69874.
+- Clang no longer warns about missing return statements (-Wreturn-type)
+ if the final statement of a non-void function is a `throw` expression
+ or a call to a function that is known to always throw. This avoids
+ false positives in code patterns where control flow is intentionally
+ terminated via exceptions.
+
Improvements to Clang's time-trace
----------------------------------
diff --git a/clang/lib/Sema/AnalysisBasedWarnings.cpp
b/clang/lib/Sema/AnalysisBasedWarnings.cpp
index 9502669612f74..ac9ba762adeb3 100644
--- a/clang/lib/Sema/AnalysisBasedWarnings.cpp
+++ b/clang/lib/Sema/AnalysisBasedWarnings.cpp
@@ -643,10 +643,7 @@ bool isKnownToAlwaysThrow(const FunctionDecl *FD) {
OnlyStmt = EWC->getSubExpr();
}
// Check if the only statement is a throw expression.
- if (isa<CXXThrowExpr>(OnlyStmt)) {
- return true; // Known to always throw.
- }
- return false; // Not known to always throw.
+ return isa<CXXThrowExpr>(OnlyStmt);
}
} // anonymous namespace
@@ -708,25 +705,23 @@ static void CheckFallThroughForBody(Sema &S, const Decl
*D, const Stmt *Body,
// If the final statement is a call to an always-throwing function,
// don't warn about the fall-through.
if (const auto *FD = dyn_cast<FunctionDecl>(D)) {
- if (const auto *CS = dyn_cast<CompoundStmt>(Body)) {
- if (!CS->body_empty()) {
- const Stmt *LastStmt = CS->body_back();
- // Unwrap ExprWithCleanups if necessary.
- if (const auto *EWC = dyn_cast<ExprWithCleanups>(LastStmt)) {
- LastStmt = EWC->getSubExpr();
- }
- if (const auto *CE = dyn_cast<CallExpr>(LastStmt)) {
- if (const FunctionDecl *Callee = CE->getDirectCallee()) {
- if (isKnownToAlwaysThrow(Callee)) {
- return; // Don't warn about fall-through.
- }
- }
- }
- // Direct throw.
- if (isa<CXXThrowExpr>(LastStmt)) {
+ if (const auto *CS = dyn_cast<CompoundStmt>(Body);
+ CS && !CS->body_empty()) {
+ const Stmt *LastStmt = CS->body_back();
+ // Unwrap ExprWithCleanups if necessary.
+ if (const auto *EWC = dyn_cast<ExprWithCleanups>(LastStmt)) {
+ LastStmt = EWC->getSubExpr();
+ }
+ if (const auto *CE = dyn_cast<CallExpr>(LastStmt)) {
+ if (const FunctionDecl *Callee = CE->getDirectCallee();
+ Callee && isKnownToAlwaysThrow(Callee)) {
return; // Don't warn about fall-through.
}
}
+ // Direct throw.
+ if (isa<CXXThrowExpr>(LastStmt)) {
+ return; // Don't warn about fall-through.
+ }
}
}
bool NotInAllControlPaths = FallThroughType == MaybeFallThrough;
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