<div dir="ltr">This is a very useful warning, thanks.<div><br></div><div>One issue I have with it is that it's disabled by Wno-tautological-compare. From the warning name that makes sense – but Wtautological-compare used to be a fairly harmless warning, so we (chromium) disabled it for a bunch of third-party libraries. When Wtautological-undefined-compare arrived, we fixed all instances of this in our code and updated our compiler to a clang that optimizes away comparisons of references with NULL (since we had fixed all of these comparisons, we thought!)</div>
<div><br>I recently realized that we didn't see Wtautological-undefined-compare warnings for all the third-party libraries that we're building with Wno-tautological-compare.</div><div><br></div><div>Do you think Wtautological-undefined-compare should be in its own warning group (and maybe have a different name to make that clear), so that folks who disabled Wtautological-compare still get this warning? The reasoning is that this warning is much more serious that what Wtautological-compare used to warn about.</div>
<div><br></div><div>Nico</div></div><div class="gmail_extra"><br><br><div class="gmail_quote">On Fri, Jun 6, 2014 at 2:39 PM, Richard Trieu <span dir="ltr"><<a href="mailto:rtrieu@google.com" target="_blank">rtrieu@google.com</a>></span> wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">Author: rtrieu<br>
Date: Fri Jun 6 16:39:26 2014<br>
New Revision: 210372<br>
<br>
URL: <a href="http://llvm.org/viewvc/llvm-project?rev=210372&view=rev" target="_blank">http://llvm.org/viewvc/llvm-project?rev=210372&view=rev</a><br>
Log:<br>
Add -Wtautological-undefined-compare and -Wundefined-bool-conversion warnings<br>
to detect underfined behavior involving pointers.<br>
<br>
Added:<br>
cfe/trunk/test/SemaCXX/warn-tautological-undefined-compare.cpp<br>
cfe/trunk/test/SemaCXX/warn-undefined-bool-conversion.cpp<br>
Modified:<br>
cfe/trunk/include/clang/Basic/DiagnosticGroups.td<br>
cfe/trunk/include/clang/Basic/DiagnosticSemaKinds.td<br>
cfe/trunk/lib/Sema/SemaChecking.cpp<br>
cfe/trunk/test/Analysis/inlining/path-notes.cpp<br>
cfe/trunk/test/Analysis/misc-ps-region-store.cpp<br>
cfe/trunk/test/Analysis/reference.cpp<br>
cfe/trunk/test/Analysis/stack-addr-ps.cpp<br>
<br>
Modified: cfe/trunk/include/clang/Basic/DiagnosticGroups.td<br>
URL: <a href="http://llvm.org/viewvc/llvm-project/cfe/trunk/include/clang/Basic/DiagnosticGroups.td?rev=210372&r1=210371&r2=210372&view=diff" target="_blank">http://llvm.org/viewvc/llvm-project/cfe/trunk/include/clang/Basic/DiagnosticGroups.td?rev=210372&r1=210371&r2=210372&view=diff</a><br>
==============================================================================<br>
--- cfe/trunk/include/clang/Basic/DiagnosticGroups.td (original)<br>
+++ cfe/trunk/include/clang/Basic/DiagnosticGroups.td Fri Jun 6 16:39:26 2014<br>
@@ -38,7 +38,9 @@ def LiteralConversion : DiagGroup<"liter<br>
def StringConversion : DiagGroup<"string-conversion">;<br>
def SignConversion : DiagGroup<"sign-conversion">;<br>
def PointerBoolConversion : DiagGroup<"pointer-bool-conversion">;<br>
-def BoolConversion : DiagGroup<"bool-conversion", [ PointerBoolConversion ] >;<br>
+def UndefinedBoolConversion : DiagGroup<"undefined-bool-conversion">;<br>
+def BoolConversion : DiagGroup<"bool-conversion", [PointerBoolConversion,<br>
+ UndefinedBoolConversion]>;<br>
def IntConversion : DiagGroup<"int-conversion">;<br>
def EnumConversion : DiagGroup<"enum-conversion">;<br>
def FloatConversion : DiagGroup<"float-conversion">;<br>
@@ -298,10 +300,12 @@ def StrncatSize : DiagGroup<"strncat-siz<br>
def TautologicalOutOfRangeCompare : DiagGroup<"tautological-constant-out-of-range-compare">;<br>
def TautologicalPointerCompare : DiagGroup<"tautological-pointer-compare">;<br>
def TautologicalOverlapCompare : DiagGroup<"tautological-overlap-compare">;<br>
+def TautologicalUndefinedCompare : DiagGroup<"tautological-undefined-compare">;<br>
def TautologicalCompare : DiagGroup<"tautological-compare",<br>
[TautologicalOutOfRangeCompare,<br>
TautologicalPointerCompare,<br>
- TautologicalOverlapCompare]>;<br>
+ TautologicalOverlapCompare,<br>
+ TautologicalUndefinedCompare]>;<br>
def HeaderHygiene : DiagGroup<"header-hygiene">;<br>
def DuplicateDeclSpecifier : DiagGroup<"duplicate-decl-specifier">;<br>
def CompareDistinctPointerType : DiagGroup<"compare-distinct-pointer-types">;<br>
<br>
Modified: cfe/trunk/include/clang/Basic/DiagnosticSemaKinds.td<br>
URL: <a href="http://llvm.org/viewvc/llvm-project/cfe/trunk/include/clang/Basic/DiagnosticSemaKinds.td?rev=210372&r1=210371&r2=210372&view=diff" target="_blank">http://llvm.org/viewvc/llvm-project/cfe/trunk/include/clang/Basic/DiagnosticSemaKinds.td?rev=210372&r1=210371&r2=210372&view=diff</a><br>
==============================================================================<br>
--- cfe/trunk/include/clang/Basic/DiagnosticSemaKinds.td (original)<br>
+++ cfe/trunk/include/clang/Basic/DiagnosticSemaKinds.td Fri Jun 6 16:39:26 2014<br>
@@ -2400,10 +2400,27 @@ def warn_impcast_pointer_to_bool : Warni<br>
"address of%select{| function| array}0 '%1' will always evaluate to "<br>
"'true'">,<br>
InGroup<PointerBoolConversion>;<br>
+def warn_this_bool_conversion : Warning<<br>
+ "'this' pointer cannot be null in well-defined C++ code; pointer may be "<br>
+ "assumed always converted to true">, InGroup<UndefinedBoolConversion>;<br>
+def warn_address_of_reference_bool_conversion : Warning<<br>
+ "reference cannot be bound to dereferenced null pointer in well-defined C++ "<br>
+ "code; pointer may be assumed always converted to true">,<br>
+ InGroup<UndefinedBoolConversion>;<br>
+<br>
def warn_null_pointer_compare : Warning<<br>
"comparison of %select{address of|function|array}0 '%1' %select{not |}2"<br>
"equal to a null pointer is always %select{true|false}2">,<br>
InGroup<TautologicalPointerCompare>;<br>
+def warn_this_null_compare : Warning<<br>
+ "'this' pointer cannot be null in well-defined C++ code; comparison may be "<br>
+ "assumed to always evaluate to %select{true|false}0">,<br>
+ InGroup<TautologicalUndefinedCompare>;<br>
+def warn_address_of_reference_null_compare : Warning<<br>
+ "reference cannot be bound to dereferenced null pointer in well-defined C++ "<br>
+ "code; comparison may be assumed to always evaluate to "<br>
+ "%select{true|false}0">,<br>
+ InGroup<TautologicalUndefinedCompare>;<br>
<br>
def note_function_warning_silence : Note<<br>
"prefix with the address-of operator to silence this warning">;<br>
<br>
Modified: cfe/trunk/lib/Sema/SemaChecking.cpp<br>
URL: <a href="http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/Sema/SemaChecking.cpp?rev=210372&r1=210371&r2=210372&view=diff" target="_blank">http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/Sema/SemaChecking.cpp?rev=210372&r1=210371&r2=210372&view=diff</a><br>
==============================================================================<br>
--- cfe/trunk/lib/Sema/SemaChecking.cpp (original)<br>
+++ cfe/trunk/lib/Sema/SemaChecking.cpp Fri Jun 6 16:39:26 2014<br>
@@ -6189,6 +6189,13 @@ void Sema::DiagnoseAlwaysNonNullPointer(<br>
<br>
const bool IsCompare = NullKind != Expr::NPCK_NotNull;<br>
<br>
+ if (isa<CXXThisExpr>(E)) {<br>
+ unsigned DiagID = IsCompare ? diag::warn_this_null_compare<br>
+ : diag::warn_this_bool_conversion;<br>
+ Diag(E->getExprLoc(), DiagID) << E->getSourceRange() << Range << IsEqual;<br>
+ return;<br>
+ }<br>
+<br>
bool IsAddressOf = false;<br>
<br>
if (UnaryOperator *UO = dyn_cast<UnaryOperator>(E)) {<br>
@@ -6218,9 +6225,14 @@ void Sema::DiagnoseAlwaysNonNullPointer(<br>
// Address of function is used to silence the function warning.<br>
if (IsFunction)<br>
return;<br>
- // Address of reference can be null.<br>
- if (T->isReferenceType())<br>
+<br>
+ if (T->isReferenceType()) {<br>
+ unsigned DiagID = IsCompare<br>
+ ? diag::warn_address_of_reference_null_compare<br>
+ : diag::warn_address_of_reference_bool_conversion;<br>
+ Diag(E->getExprLoc(), DiagID) << E->getSourceRange() << Range << IsEqual;<br>
return;<br>
+ }<br>
}<br>
<br>
// Found nothing.<br>
<br>
Modified: cfe/trunk/test/Analysis/inlining/path-notes.cpp<br>
URL: <a href="http://llvm.org/viewvc/llvm-project/cfe/trunk/test/Analysis/inlining/path-notes.cpp?rev=210372&r1=210371&r2=210372&view=diff" target="_blank">http://llvm.org/viewvc/llvm-project/cfe/trunk/test/Analysis/inlining/path-notes.cpp?rev=210372&r1=210371&r2=210372&view=diff</a><br>
==============================================================================<br>
--- cfe/trunk/test/Analysis/inlining/path-notes.cpp (original)<br>
+++ cfe/trunk/test/Analysis/inlining/path-notes.cpp Fri Jun 6 16:39:26 2014<br>
@@ -1,5 +1,5 @@<br>
-// RUN: %clang_cc1 -analyze -analyzer-checker=core -analyzer-output=text -analyzer-config c++-inlining=destructors -std=c++11 -verify %s<br>
-// RUN: %clang_cc1 -analyze -analyzer-checker=core -analyzer-output=plist-multi-file -analyzer-config c++-inlining=destructors -std=c++11 -analyzer-config path-diagnostics-alternate=false %s -o %t.plist<br>
+// RUN: %clang_cc1 -analyze -analyzer-checker=core -analyzer-output=text -analyzer-config c++-inlining=destructors -std=c++11 -verify -Wno-tautological-undefined-compare %s<br>
+// RUN: %clang_cc1 -analyze -analyzer-checker=core -analyzer-output=plist-multi-file -analyzer-config c++-inlining=destructors -std=c++11 -analyzer-config path-diagnostics-alternate=false %s -o %t.plist -Wno-tautological-undefined-compare<br>
// RUN: FileCheck --input-file=%t.plist %s<br>
<br>
class Foo {<br>
<br>
Modified: cfe/trunk/test/Analysis/misc-ps-region-store.cpp<br>
URL: <a href="http://llvm.org/viewvc/llvm-project/cfe/trunk/test/Analysis/misc-ps-region-store.cpp?rev=210372&r1=210371&r2=210372&view=diff" target="_blank">http://llvm.org/viewvc/llvm-project/cfe/trunk/test/Analysis/misc-ps-region-store.cpp?rev=210372&r1=210371&r2=210372&view=diff</a><br>
==============================================================================<br>
--- cfe/trunk/test/Analysis/misc-ps-region-store.cpp (original)<br>
+++ cfe/trunk/test/Analysis/misc-ps-region-store.cpp Fri Jun 6 16:39:26 2014<br>
@@ -1,5 +1,5 @@<br>
-// RUN: %clang_cc1 -triple i386-apple-darwin9 -analyze -analyzer-checker=core,alpha.core,debug.ExprInspection -analyzer-store=region -verify -fblocks -analyzer-opt-analyze-nested-blocks %s -fexceptions -fcxx-exceptions<br>
-// RUN: %clang_cc1 -triple x86_64-apple-darwin9 -analyze -analyzer-checker=core,alpha.core,debug.ExprInspection -analyzer-store=region -verify -fblocks -analyzer-opt-analyze-nested-blocks %s -fexceptions -fcxx-exceptions<br>
+// RUN: %clang_cc1 -triple i386-apple-darwin9 -analyze -analyzer-checker=core,alpha.core,debug.ExprInspection -analyzer-store=region -verify -fblocks -analyzer-opt-analyze-nested-blocks %s -fexceptions -fcxx-exceptions -Wno-tautological-undefined-compare<br>
+// RUN: %clang_cc1 -triple x86_64-apple-darwin9 -analyze -analyzer-checker=core,alpha.core,debug.ExprInspection -analyzer-store=region -verify -fblocks -analyzer-opt-analyze-nested-blocks %s -fexceptions -fcxx-exceptions -Wno-tautological-undefined-compare<br>
<br>
void clang_analyzer_warnIfReached();<br>
<br>
<br>
Modified: cfe/trunk/test/Analysis/reference.cpp<br>
URL: <a href="http://llvm.org/viewvc/llvm-project/cfe/trunk/test/Analysis/reference.cpp?rev=210372&r1=210371&r2=210372&view=diff" target="_blank">http://llvm.org/viewvc/llvm-project/cfe/trunk/test/Analysis/reference.cpp?rev=210372&r1=210371&r2=210372&view=diff</a><br>
==============================================================================<br>
--- cfe/trunk/test/Analysis/reference.cpp (original)<br>
+++ cfe/trunk/test/Analysis/reference.cpp Fri Jun 6 16:39:26 2014<br>
@@ -1,4 +1,4 @@<br>
-// RUN: %clang_cc1 -analyze -analyzer-checker=core,alpha.core,debug.ExprInspection -analyzer-store=region -analyzer-constraints=range -verify -Wno-null-dereference %s<br>
+// RUN: %clang_cc1 -analyze -analyzer-checker=core,alpha.core,debug.ExprInspection -analyzer-store=region -analyzer-constraints=range -verify -Wno-null-dereference -Wno-tautological-undefined-compare %s<br>
<br>
void clang_analyzer_eval(bool);<br>
<br>
<br>
Modified: cfe/trunk/test/Analysis/stack-addr-ps.cpp<br>
URL: <a href="http://llvm.org/viewvc/llvm-project/cfe/trunk/test/Analysis/stack-addr-ps.cpp?rev=210372&r1=210371&r2=210372&view=diff" target="_blank">http://llvm.org/viewvc/llvm-project/cfe/trunk/test/Analysis/stack-addr-ps.cpp?rev=210372&r1=210371&r2=210372&view=diff</a><br>
==============================================================================<br>
--- cfe/trunk/test/Analysis/stack-addr-ps.cpp (original)<br>
+++ cfe/trunk/test/Analysis/stack-addr-ps.cpp Fri Jun 6 16:39:26 2014<br>
@@ -1,4 +1,4 @@<br>
-// RUN: %clang_cc1 -analyze -analyzer-checker=core -analyzer-store=region -verify %s<br>
+// RUN: %clang_cc1 -analyze -analyzer-checker=core -analyzer-store=region -verify %s -Wno-undefined-bool-conversion<br>
<br>
typedef __INTPTR_TYPE__ intptr_t;<br>
<br>
<br>
Added: cfe/trunk/test/SemaCXX/warn-tautological-undefined-compare.cpp<br>
URL: <a href="http://llvm.org/viewvc/llvm-project/cfe/trunk/test/SemaCXX/warn-tautological-undefined-compare.cpp?rev=210372&view=auto" target="_blank">http://llvm.org/viewvc/llvm-project/cfe/trunk/test/SemaCXX/warn-tautological-undefined-compare.cpp?rev=210372&view=auto</a><br>
==============================================================================<br>
--- cfe/trunk/test/SemaCXX/warn-tautological-undefined-compare.cpp (added)<br>
+++ cfe/trunk/test/SemaCXX/warn-tautological-undefined-compare.cpp Fri Jun 6 16:39:26 2014<br>
@@ -0,0 +1,34 @@<br>
+// RUN: %clang_cc1 -fsyntax-only -verify %s<br>
+// RUN: %clang_cc1 -fsyntax-only -verify -Wtautological-undefined-compare %s<br>
+// RUN: %clang_cc1 -fsyntax-only -verify -Wno-tautological-compare -Wtautological-undefined-compare %s<br>
+// RUN: %clang_cc1 -fsyntax-only -verify -Wtautological-compare %s<br>
+<br>
+void test1(int &x) {<br>
+ if (x == 1) { }<br>
+ if (&x == 0) { }<br>
+ // expected-warning@-1{{reference cannot be bound to dereferenced null pointer in well-defined C++ code; comparison may be assumed to always evaluate to false}}<br>
+ if (&x != 0) { }<br>
+ // expected-warning@-1{{reference cannot be bound to dereferenced null pointer in well-defined C++ code; comparison may be assumed to always evaluate to true}}<br>
+}<br>
+<br>
+class test2 {<br>
+ test2() : x(y) {}<br>
+<br>
+ void foo() {<br>
+ if (this == 0) { }<br>
+ // expected-warning@-1{{'this' pointer cannot be null in well-defined C++ code; comparison may be assumed to always evaluate to false}}<br>
+ if (this != 0) { }<br>
+ // expected-warning@-1{{'this' pointer cannot be null in well-defined C++ code; comparison may be assumed to always evaluate to true}}<br>
+ }<br>
+<br>
+ void bar() {<br>
+ if (x == 1) { }<br>
+ if (&x == 0) { }<br>
+ // expected-warning@-1{{reference cannot be bound to dereferenced null pointer in well-defined C++ code; comparison may be assumed to always evaluate to false}}<br>
+ if (&x != 0) { }<br>
+ // expected-warning@-1{{reference cannot be bound to dereferenced null pointer in well-defined C++ code; comparison may be assumed to always evaluate to true}}<br>
+ }<br>
+<br>
+ int &x;<br>
+ int y;<br>
+};<br>
<br>
Added: cfe/trunk/test/SemaCXX/warn-undefined-bool-conversion.cpp<br>
URL: <a href="http://llvm.org/viewvc/llvm-project/cfe/trunk/test/SemaCXX/warn-undefined-bool-conversion.cpp?rev=210372&view=auto" target="_blank">http://llvm.org/viewvc/llvm-project/cfe/trunk/test/SemaCXX/warn-undefined-bool-conversion.cpp?rev=210372&view=auto</a><br>
==============================================================================<br>
--- cfe/trunk/test/SemaCXX/warn-undefined-bool-conversion.cpp (added)<br>
+++ cfe/trunk/test/SemaCXX/warn-undefined-bool-conversion.cpp Fri Jun 6 16:39:26 2014<br>
@@ -0,0 +1,37 @@<br>
+// RUN: %clang_cc1 -fsyntax-only -verify %s<br>
+// RUN: %clang_cc1 -fsyntax-only -verify -Wundefined-bool-conversion %s<br>
+// RUN: %clang_cc1 -fsyntax-only -verify -Wno-bool-conversion -Wundefined-bool-conversion %s<br>
+// RUN: %clang_cc1 -fsyntax-only -verify -Wbool-conversion %s<br>
+<br>
+void test1(int &x) {<br>
+ if (x == 1) { }<br>
+ if (&x) { }<br>
+ // expected-warning@-1{{reference cannot be bound to dereferenced null pointer in well-defined C++ code; pointer may be assumed always converted to true}}<br>
+<br>
+ if (!&x) { }<br>
+ // expected-warning@-1{{reference cannot be bound to dereferenced null pointer in well-defined C++ code; pointer may be assumed always converted to true}}<br>
+}<br>
+<br>
+class test2 {<br>
+ test2() : x(y) {}<br>
+<br>
+ void foo() {<br>
+ if (this) { }<br>
+ // expected-warning@-1{{'this' pointer cannot be null in well-defined C++ code; pointer may be assumed always converted to true}}<br>
+<br>
+ if (!this) { }<br>
+ // expected-warning@-1{{'this' pointer cannot be null in well-defined C++ code; pointer may be assumed always converted to true}}<br>
+ }<br>
+<br>
+ void bar() {<br>
+ if (x == 1) { }<br>
+ if (&x) { }<br>
+ // expected-warning@-1{{reference cannot be bound to dereferenced null pointer in well-defined C++ code; pointer may be assumed always converted to true}}<br>
+<br>
+ if (!&x) { }<br>
+ // expected-warning@-1{{reference cannot be bound to dereferenced null pointer in well-defined C++ code; pointer may be assumed always converted to true}}<br>
+ }<br>
+<br>
+ int &x;<br>
+ int y;<br>
+};<br>
<br>
<br>
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</blockquote></div><br></div>