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authorRichard Trieu <rtrieu@google.com>2019-10-19 00:57:23 +0000
committerRichard Trieu <rtrieu@google.com>2019-10-19 00:57:23 +0000
commita27ae544f30bfd7dc765b8a6080190d39d893b99 (patch)
tree20f6b66320ee0e421f33e6e54eab73db57932762
parent7decfe83555385bebac2e4bed35035f3b0f4d666 (diff)
downloadclang-a27ae544f30bfd7dc765b8a6080190d39d893b99.tar.gz
New tautological warning for bitwise-or with non-zero constant always true.
Taking a value and the bitwise-or it with a non-zero constant will always result in a non-zero value. In a boolean context, this is always true. if (x | 0x4) {} // always true, intended '&' This patch creates a new warning group -Wtautological-bitwise-compare for this warning. It also moves in the existing tautological bitwise comparisons into this group. A few other changes were needed to the CFGBuilder so that all bool contexts would be checked. The warnings in -Wtautological-bitwise-compare will be off by default due to using the CFG. Fixes: https://bugs.llvm.org/show_bug.cgi?id=42666 Differential Revision: https://reviews.llvm.org/D66046 git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@375318 91177308-0d34-0410-b5e6-96231b3b80d8
-rw-r--r--docs/ReleaseNotes.rst5
-rw-r--r--include/clang/Analysis/CFG.h1
-rw-r--r--include/clang/Basic/DiagnosticGroups.td2
-rw-r--r--include/clang/Basic/DiagnosticSemaKinds.td5
-rw-r--r--lib/Analysis/CFG.cpp41
-rw-r--r--lib/Sema/AnalysisBasedWarnings.cpp24
-rw-r--r--test/Sema/warn-bitwise-compare.c21
-rw-r--r--test/SemaCXX/warn-bitwise-compare.cpp12
8 files changed, 102 insertions, 9 deletions
diff --git a/docs/ReleaseNotes.rst b/docs/ReleaseNotes.rst
index 37dbac3090..41dea299e6 100644
--- a/docs/ReleaseNotes.rst
+++ b/docs/ReleaseNotes.rst
@@ -56,6 +56,11 @@ Improvements to Clang's diagnostics
- -Wtautological-compare for self comparisons and
-Wtautological-overlap-compare will now look through member and array
access to determine if two operand expressions are the same.
+- -Wtautological-bitwise-compare is a new warning group. This group has the
+ current warning which diagnoses the tautological comparison of a bitwise
+ operation and a constant. The group also has the new warning which diagnoses
+ when a bitwise-or with a non-negative value is converted to a bool, since
+ that bool will always be true.
Non-comprehensive list of changes in this release
-------------------------------------------------
diff --git a/include/clang/Analysis/CFG.h b/include/clang/Analysis/CFG.h
index b24e32c966..a8301a0e00 100644
--- a/include/clang/Analysis/CFG.h
+++ b/include/clang/Analysis/CFG.h
@@ -1213,6 +1213,7 @@ public:
virtual void compareAlwaysTrue(const BinaryOperator *B, bool isAlwaysTrue) {}
virtual void compareBitwiseEquality(const BinaryOperator *B,
bool isAlwaysTrue) {}
+ virtual void compareBitwiseOr(const BinaryOperator *B) {}
};
/// Represents a source-level, intra-procedural CFG that represents the
diff --git a/include/clang/Basic/DiagnosticGroups.td b/include/clang/Basic/DiagnosticGroups.td
index 396f297881..3573ebdfc6 100644
--- a/include/clang/Basic/DiagnosticGroups.td
+++ b/include/clang/Basic/DiagnosticGroups.td
@@ -516,12 +516,14 @@ def TautologicalConstantCompare : DiagGroup<"tautological-constant-compare",
[TautologicalOutOfRangeCompare]>;
def TautologicalPointerCompare : DiagGroup<"tautological-pointer-compare">;
def TautologicalOverlapCompare : DiagGroup<"tautological-overlap-compare">;
+def TautologicalBitwiseCompare : DiagGroup<"tautological-bitwise-compare">;
def TautologicalUndefinedCompare : DiagGroup<"tautological-undefined-compare">;
def TautologicalObjCBoolCompare : DiagGroup<"tautological-objc-bool-compare">;
def TautologicalCompare : DiagGroup<"tautological-compare",
[TautologicalConstantCompare,
TautologicalPointerCompare,
TautologicalOverlapCompare,
+ TautologicalBitwiseCompare,
TautologicalUndefinedCompare,
TautologicalObjCBoolCompare]>;
def HeaderHygiene : DiagGroup<"header-hygiene">;
diff --git a/include/clang/Basic/DiagnosticSemaKinds.td b/include/clang/Basic/DiagnosticSemaKinds.td
index e41cfe2fe7..98fce04e66 100644
--- a/include/clang/Basic/DiagnosticSemaKinds.td
+++ b/include/clang/Basic/DiagnosticSemaKinds.td
@@ -8332,7 +8332,10 @@ def warn_comparison_always : Warning<
InGroup<TautologicalCompare>;
def warn_comparison_bitwise_always : Warning<
"bitwise comparison always evaluates to %select{false|true}0">,
- InGroup<TautologicalCompare>;
+ InGroup<TautologicalBitwiseCompare>, DefaultIgnore;
+def warn_comparison_bitwise_or : Warning<
+ "bitwise or with non-zero value always evaluates to true">,
+ InGroup<TautologicalBitwiseCompare>, DefaultIgnore;
def warn_tautological_overlap_comparison : Warning<
"overlapping comparisons always evaluate to %select{false|true}0">,
InGroup<TautologicalOverlapCompare>, DefaultIgnore;
diff --git a/lib/Analysis/CFG.cpp b/lib/Analysis/CFG.cpp
index 54fb388b0c..a533a8d97b 100644
--- a/lib/Analysis/CFG.cpp
+++ b/lib/Analysis/CFG.cpp
@@ -1139,6 +1139,31 @@ private:
return {};
}
+ /// A bitwise-or with a non-zero constant always evaluates to true.
+ TryResult checkIncorrectBitwiseOrOperator(const BinaryOperator *B) {
+ const Expr *LHSConstant =
+ tryTransformToIntOrEnumConstant(B->getLHS()->IgnoreParenImpCasts());
+ const Expr *RHSConstant =
+ tryTransformToIntOrEnumConstant(B->getRHS()->IgnoreParenImpCasts());
+
+ if ((LHSConstant && RHSConstant) || (!LHSConstant && !RHSConstant))
+ return {};
+
+ const Expr *Constant = LHSConstant ? LHSConstant : RHSConstant;
+
+ Expr::EvalResult Result;
+ if (!Constant->EvaluateAsInt(Result, *Context))
+ return {};
+
+ if (Result.Val.getInt() == 0)
+ return {};
+
+ if (BuildOpts.Observer)
+ BuildOpts.Observer->compareBitwiseOr(B);
+
+ return TryResult(true);
+ }
+
/// Try and evaluate an expression to an integer constant.
bool tryEvaluate(Expr *S, Expr::EvalResult &outResult) {
if (!BuildOpts.PruneTriviallyFalseEdges)
@@ -1156,7 +1181,7 @@ private:
return {};
if (BinaryOperator *Bop = dyn_cast<BinaryOperator>(S)) {
- if (Bop->isLogicalOp()) {
+ if (Bop->isLogicalOp() || Bop->isEqualityOp()) {
// Check the cache first.
CachedBoolEvalsTy::iterator I = CachedBoolEvals.find(S);
if (I != CachedBoolEvals.end())
@@ -1240,6 +1265,10 @@ private:
TryResult BopRes = checkIncorrectRelationalOperator(Bop);
if (BopRes.isKnown())
return BopRes.isTrue();
+ } else if (Bop->getOpcode() == BO_Or) {
+ TryResult BopRes = checkIncorrectBitwiseOrOperator(Bop);
+ if (BopRes.isKnown())
+ return BopRes.isTrue();
}
}
@@ -2340,6 +2369,9 @@ CFGBlock *CFGBuilder::VisitUnaryOperator(UnaryOperator *U,
appendStmt(Block, U);
}
+ if (U->getOpcode() == UO_LNot)
+ tryEvaluateBool(U->getSubExpr()->IgnoreParens());
+
return Visit(U->getSubExpr(), AddStmtChoice());
}
@@ -2474,6 +2506,9 @@ CFGBlock *CFGBuilder::VisitBinaryOperator(BinaryOperator *B,
appendStmt(Block, B);
}
+ if (B->isEqualityOp() || B->isRelationalOp())
+ tryEvaluateBool(B);
+
CFGBlock *RBlock = Visit(B->getRHS());
CFGBlock *LBlock = Visit(B->getLHS());
// If visiting RHS causes us to finish 'Block', e.g. the RHS is a StmtExpr
@@ -4527,6 +4562,10 @@ CFGBlock *CFGBuilder::VisitImplicitCastExpr(ImplicitCastExpr *E,
autoCreateBlock();
appendStmt(Block, E);
}
+
+ if (E->getCastKind() == CK_IntegralToBoolean)
+ tryEvaluateBool(E->getSubExpr()->IgnoreParens());
+
return Visit(E->getSubExpr(), AddStmtChoice());
}
diff --git a/lib/Sema/AnalysisBasedWarnings.cpp b/lib/Sema/AnalysisBasedWarnings.cpp
index 01648fea8d..2c70c0599e 100644
--- a/lib/Sema/AnalysisBasedWarnings.cpp
+++ b/lib/Sema/AnalysisBasedWarnings.cpp
@@ -159,6 +159,20 @@ public:
S.Diag(B->getExprLoc(), diag::warn_comparison_bitwise_always)
<< DiagRange << isAlwaysTrue;
}
+
+ void compareBitwiseOr(const BinaryOperator *B) override {
+ if (HasMacroID(B))
+ return;
+
+ SourceRange DiagRange = B->getSourceRange();
+ S.Diag(B->getExprLoc(), diag::warn_comparison_bitwise_or) << DiagRange;
+ }
+
+ static bool hasActiveDiagnostics(DiagnosticsEngine &Diags,
+ SourceLocation Loc) {
+ return !Diags.isIgnored(diag::warn_tautological_overlap_comparison, Loc) ||
+ !Diags.isIgnored(diag::warn_comparison_bitwise_or, Loc);
+ }
};
} // anonymous namespace
@@ -2070,10 +2084,9 @@ AnalysisBasedWarnings::IssueWarnings(sema::AnalysisBasedWarnings::Policy P,
.setAlwaysAdd(Stmt::AttributedStmtClass);
}
- // Install the logical handler for -Wtautological-overlap-compare
+ // Install the logical handler.
llvm::Optional<LogicalErrorHandler> LEH;
- if (!Diags.isIgnored(diag::warn_tautological_overlap_comparison,
- D->getBeginLoc())) {
+ if (LogicalErrorHandler::hasActiveDiagnostics(Diags, D->getBeginLoc())) {
LEH.emplace(S);
AC.getCFGBuildOptions().Observer = &*LEH;
}
@@ -2222,9 +2235,8 @@ AnalysisBasedWarnings::IssueWarnings(sema::AnalysisBasedWarnings::Policy P,
checkThrowInNonThrowingFunc(S, FD, AC);
// If none of the previous checks caused a CFG build, trigger one here
- // for -Wtautological-overlap-compare
- if (!Diags.isIgnored(diag::warn_tautological_overlap_comparison,
- D->getBeginLoc())) {
+ // for the logical error handler.
+ if (LogicalErrorHandler::hasActiveDiagnostics(Diags, D->getBeginLoc())) {
AC.getCFG();
}
diff --git a/test/Sema/warn-bitwise-compare.c b/test/Sema/warn-bitwise-compare.c
index 175f8f5367..d08f1bf13f 100644
--- a/test/Sema/warn-bitwise-compare.c
+++ b/test/Sema/warn-bitwise-compare.c
@@ -1,7 +1,12 @@
-// RUN: %clang_cc1 -fsyntax-only -verify -Wtautological-compare %s
+// RUN: %clang_cc1 -fsyntax-only -verify -Wtautological-bitwise-compare %s
#define mydefine 2
+enum {
+ ZERO,
+ ONE,
+};
+
void f(int x) {
if ((8 & x) == 3) {} // expected-warning {{bitwise comparison always evaluates to false}}
if ((x & 8) == 4) {} // expected-warning {{bitwise comparison always evaluates to false}}
@@ -13,6 +18,9 @@ void f(int x) {
if ((x & 0x15) == 0x13) {} // expected-warning {{bitwise comparison always evaluates to false}}
if ((0x23 | x) == 0x155){} // expected-warning {{bitwise comparison always evaluates to false}}
+ if (!!((8 & x) == 3)) {} // expected-warning {{bitwise comparison always evaluates to false}}
+ int y = ((8 & x) == 3) ? 1 : 2; // expected-warning {{bitwise comparison always evaluates to false}}
+
if ((x & 8) == 8) {}
if ((x & 8) != 8) {}
if ((x | 4) == 4) {}
@@ -26,3 +34,14 @@ void f(int x) {
if ((x & mydefine) == 8) {}
if ((x | mydefine) == 4) {}
}
+
+void g(int x) {
+ if (x | 5) {} // expected-warning {{bitwise or with non-zero value always evaluates to true}}
+ if (5 | x) {} // expected-warning {{bitwise or with non-zero value always evaluates to true}}
+ if (!((x | 5))) {} // expected-warning {{bitwise or with non-zero value always evaluates to true}}
+
+ if (x | -1) {} // expected-warning {{bitwise or with non-zero value always evaluates to true}}
+ if (x | ONE) {} // expected-warning {{bitwise or with non-zero value always evaluates to true}}
+
+ if (x | ZERO) {}
+}
diff --git a/test/SemaCXX/warn-bitwise-compare.cpp b/test/SemaCXX/warn-bitwise-compare.cpp
new file mode 100644
index 0000000000..894d4c581e
--- /dev/null
+++ b/test/SemaCXX/warn-bitwise-compare.cpp
@@ -0,0 +1,12 @@
+// RUN: %clang_cc1 -fsyntax-only -verify -Wtautological-bitwise-compare %s
+
+void test(int x) {
+ bool b1 = (8 & x) == 3;
+ // expected-warning@-1 {{bitwise comparison always evaluates to false}}
+ bool b2 = x | 5;
+ // expected-warning@-1 {{bitwise or with non-zero value always evaluates to true}}
+ bool b3 = (x | 5);
+ // expected-warning@-1 {{bitwise or with non-zero value always evaluates to true}}
+ bool b4 = !!(x | 5);
+ // expected-warning@-1 {{bitwise or with non-zero value always evaluates to true}}
+}