[clang] [Clang] eliminate -Winvalid-noreturn false positive after throw + unreachable try/catch blocks (PR #175443)
Oleksandr T. via cfe-commits
cfe-commits at lists.llvm.org
Sun Jan 11 08:41:47 PST 2026
https://github.com/a-tarasyuk created https://github.com/llvm/llvm-project/pull/175443
Fixes #174822
---
This PR fixes a false `-Winvalid-noreturn` positive when an unconditional `throw` is followed by an unreachable `try`/`catch` block.
The false positive occurred because reachability analysis marked `try`/`catch` regions as live even when unreachable via normal control flow. The following logic
https://github.com/llvm/llvm-project/blob/1c0c9aeae681dbed90fcb19edd8a41e10a17f867/clang/lib/Sema/AnalysisBasedWarnings.cpp#L573-L589
that adjusted for missing `EH` call edges, treated disconnected `try` as reachable.
CFG construction now keeps the `try` dispatch block as the join point of the `try` statement and adds a successor for the `try` body. If the `try` body is empty, an empty block is created and connected to the successor. This prevents the `try` dispatch from becoming disconnected and ensures that return paths in _function-try-blocks_
https://github.com/llvm/llvm-project/blob/1c0c9aeae681dbed90fcb19edd8a41e10a17f867/clang/test/SemaCXX/return-noreturn.cpp#L249-L264
Also, unreachable try/catch code after an unconditional `throw` is no longer treated as reachable and no longer triggers a false positive `-Winvalid-noreturn` warning.
>From 5c9260a48009c1de6ec6439fa3ca7083f070986c Mon Sep 17 00:00:00 2001
From: Oleksandr Tarasiuk <oleksandr.tarasiuk at outlook.com>
Date: Sun, 11 Jan 2026 17:37:56 +0200
Subject: [PATCH] [Clang] eliminate -Winvalid-noreturn false positive after
throw + unreachable try/catch blocks
---
clang/docs/ReleaseNotes.rst | 1 +
clang/lib/Analysis/CFG.cpp | 13 ++++++++++--
clang/lib/Sema/AnalysisBasedWarnings.cpp | 21 +------------------
.../Analysis/auto-obj-dtors-cfg-output.cpp | 20 ++++++++++++------
clang/test/Analysis/misc-ps-region-store.cpp | 4 ++--
clang/test/SemaCXX/return-noreturn.cpp | 7 +++++++
6 files changed, 36 insertions(+), 30 deletions(-)
diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index c4384fcea5504..31cfd05254a60 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -564,6 +564,7 @@ Bug Fixes in This Version
- Fixed a crash when parsing malformed #pragma clang loop vectorize_width(4,8,16)
by diagnosing invalid comma-separated argument lists. (#GH166325)
- Clang now treats enumeration constants of fixed-underlying enums as the enumerated type. (#GH172118)
+- Fixed a ``-Winvalid-noreturn`` false positive for unreachable ``try`` blocks following an unconditional ``throw``. (#GH174822)
Bug Fixes to Compiler Builtins
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
diff --git a/clang/lib/Analysis/CFG.cpp b/clang/lib/Analysis/CFG.cpp
index f8a2afec79700..4531cbc29f338 100644
--- a/clang/lib/Analysis/CFG.cpp
+++ b/clang/lib/Analysis/CFG.cpp
@@ -4740,11 +4740,20 @@ CFGBlock *CFGBuilder::VisitCXXTryStmt(CXXTryStmt *Terminator) {
// Save the current "try" context.
SaveAndRestore SaveTry(TryTerminatedBlock, NewTryTerminatedBlock);
- cfg->addTryDispatchBlock(TryTerminatedBlock);
+ cfg->addTryDispatchBlock(NewTryTerminatedBlock);
assert(Terminator->getTryBlock() && "try must contain a non-NULL body");
Block = nullptr;
- return addStmt(Terminator->getTryBlock());
+
+ CFGBlock *TryBodyEntry = addStmt(Terminator->getTryBlock());
+ if (TryBodyEntry) {
+ addSuccessor(NewTryTerminatedBlock, TryBodyEntry);
+ } else {
+ CFGBlock *EmptyTryBody = createBlock(/*add_successor*/ false);
+ addSuccessor(NewTryTerminatedBlock, EmptyTryBody);
+ addSuccessor(EmptyTryBody, TrySuccessor);
+ }
+ return NewTryTerminatedBlock;
}
CFGBlock *CFGBuilder::VisitCXXCatchStmt(CXXCatchStmt *CS) {
diff --git a/clang/lib/Sema/AnalysisBasedWarnings.cpp b/clang/lib/Sema/AnalysisBasedWarnings.cpp
index 7b08648080710..99e59b361a187 100644
--- a/clang/lib/Sema/AnalysisBasedWarnings.cpp
+++ b/clang/lib/Sema/AnalysisBasedWarnings.cpp
@@ -567,26 +567,7 @@ static ControlFlowKind CheckFallThrough(AnalysisDeclContext &AC) {
// The CFG leaves in dead things, and we don't want the dead code paths to
// confuse us, so we mark all live things first.
llvm::BitVector live(cfg->getNumBlockIDs());
- unsigned count = reachable_code::ScanReachableFromBlock(&cfg->getEntry(),
- live);
-
- bool AddEHEdges = AC.getAddEHEdges();
- if (!AddEHEdges && count != cfg->getNumBlockIDs())
- // When there are things remaining dead, and we didn't add EH edges
- // from CallExprs to the catch clauses, we have to go back and
- // mark them as live.
- for (const auto *B : *cfg) {
- if (!live[B->getBlockID()]) {
- if (B->preds().empty()) {
- const Stmt *Term = B->getTerminatorStmt();
- if (isa_and_nonnull<CXXTryStmt>(Term))
- // When not adding EH edges from calls, catch clauses
- // can otherwise seem dead. Avoid noting them as dead.
- count += reachable_code::ScanReachableFromBlock(B, live);
- continue;
- }
- }
- }
+ reachable_code::ScanReachableFromBlock(&cfg->getEntry(), live);
// Now we know what is live, we check the live precessors of the exit block
// and look for fall through paths, being careful to ignore normal returns,
diff --git a/clang/test/Analysis/auto-obj-dtors-cfg-output.cpp b/clang/test/Analysis/auto-obj-dtors-cfg-output.cpp
index 96b9a5508cc08..882f30a7120a3 100644
--- a/clang/test/Analysis/auto-obj-dtors-cfg-output.cpp
+++ b/clang/test/Analysis/auto-obj-dtors-cfg-output.cpp
@@ -1296,17 +1296,21 @@ void test_for_inc_conditional() {
(void)0;
}
-// CHECK: [B3 (ENTRY)]
-// CHECK-NEXT: Succs (1): B0
+// CHECK: [B4 (ENTRY)]
+// CHECK-NEXT: Succs (1): B1
// CHECK: [B1]
// CHECK-NEXT: T: try ...
-// CHECK-NEXT: Succs (2): B2 B0
+// CHECK-NEXT: Preds (1): B4
+// CHECK-NEXT: Succs (3): B2 B0 B3
// CHECK: [B2]
// CHECK-NEXT: catch (const A &e):
// CHECK-NEXT: 1: catch (const A &e) {
// CHECK-NEXT: }
// CHECK-NEXT: Preds (1): B1
// CHECK-NEXT: Succs (1): B0
+// CHECK: [B3]
+// CHECK-NEXT: Preds (1): B1
+// CHECK-NEXT: Succs (1): B0
// CHECK: [B0 (EXIT)]
// CHECK-NEXT: Preds (3): B2 B1 B3
void test_catch_const_ref() {
@@ -1315,11 +1319,12 @@ void test_catch_const_ref() {
}
}
-// CHECK: [B3 (ENTRY)]
-// CHECK-NEXT: Succs (1): B0
+// CHECK: [B4 (ENTRY)]
+// CHECK-NEXT: Succs (1): B1
// CHECK: [B1]
// CHECK-NEXT: T: try ...
-// CHECK-NEXT: Succs (2): B2 B0
+// CHECK-NEXT: Preds (1): B4
+// CHECK-NEXT: Succs (3): B2 B0 B3
// CHECK: [B2]
// CHECK-NEXT: catch (A e):
// CHECK-NEXT: 1: catch (A e) {
@@ -1327,6 +1332,9 @@ void test_catch_const_ref() {
// CHECK-NEXT: 2: [B2.1].~A() (Implicit destructor)
// CHECK-NEXT: Preds (1): B1
// CHECK-NEXT: Succs (1): B0
+// CHECK: [B3]
+// CHECK-NEXT: Preds (1): B1
+// CHECK-NEXT: Succs (1): B0
// CHECK: [B0 (EXIT)]
// CHECK-NEXT: Preds (3): B2 B1 B3
void test_catch_copy() {
diff --git a/clang/test/Analysis/misc-ps-region-store.cpp b/clang/test/Analysis/misc-ps-region-store.cpp
index 958ad5ea40ea5..7d9c7bf634459 100644
--- a/clang/test/Analysis/misc-ps-region-store.cpp
+++ b/clang/test/Analysis/misc-ps-region-store.cpp
@@ -526,7 +526,7 @@ MyEnum rdar10892489_positive() {
} catch (MyEnum e) {
int *p = 0;
// FALSE NEGATIVE
- *p = 0xDEADBEEF; // {{null}}
+ *p = 0xDEADBEEF; // expected-warning {{Dereference of null pointer (loaded from variable 'p')}}
return e;
}
return MyEnumValue;
@@ -552,7 +552,7 @@ void PR11545_positive() {
{
int *p = 0;
// FALSE NEGATIVE
- *p = 0xDEADBEEF; // {{null}}
+ *p = 0xDEADBEEF; // expected-warning {{Dereference of null pointer (loaded from variable 'p')}}
}
}
diff --git a/clang/test/SemaCXX/return-noreturn.cpp b/clang/test/SemaCXX/return-noreturn.cpp
index 873e4c7e12f23..9137534c5149b 100644
--- a/clang/test/SemaCXX/return-noreturn.cpp
+++ b/clang/test/SemaCXX/return-noreturn.cpp
@@ -262,3 +262,10 @@ int functionTryBlock3(int s) try {
} catch (...) {
return 0;
} // ok, both paths return.
+
+namespace GH174822 {
+[[noreturn]] void t() {
+ throw 1;
+ try {} catch(...) {}
+}
+}
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