From 5f5ef97906ab54fd9f60f8b30894af4af9394b5e Mon Sep 17 00:00:00 2001 From: Ted Kremenek Date: Sat, 15 Mar 2014 01:26:32 +0000 Subject: [PATCH] Start breaking -Wunreachable-code up into different diagnostic groups. Recent work on -Wunreachable-code has focused on suppressing uninteresting unreachable code that center around "configuration values", but there are still some set of cases that are sometimes interesting or uninteresting depending on the codebase. For example, a dead "break" statement may not be interesting for a particular codebase, potentially because it is auto-generated or simply because code is written defensively. To address these workflow differences, -Wunreachable-code is now broken into several diagnostic groups: -Wunreachable-code: intended to be a reasonable "default" for most users. and then other groups that turn on more aggressive checking: -Wunreachable-code-break: warn about dead break statements -Wunreachable-code-trivial-return: warn about dead return statements that return "trivial" values (e.g., return 0). Other return statements that return non-trivial values are still reported under -Wunreachable-code (this is an area subject to more refinement). -Wunreachable-code-aggressive: supergroup that enables all these groups. The goal is to eventually make -Wunreachable-code good enough to either be in -Wall or on-by-default, thus finessing these warnings into different groups helps achieve maximum signal for more users. TODO: the tests need to be updated to reflect this extra control via diagnostic flags. git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@203994 91177308-0d34-0410-b5e6-96231b3b80d8 --- .../clang/Analysis/Analyses/ReachableCode.h | 10 ++- include/clang/Basic/DiagnosticGroups.td | 15 +++++ include/clang/Basic/DiagnosticSemaKinds.td | 13 +++- lib/Analysis/ReachableCode.cpp | 62 ++++++++++++------- lib/Sema/AnalysisBasedWarnings.cpp | 17 ++++- test/Sema/warn-unreachable.c | 2 +- test/SemaCXX/unreachable-code.cpp | 2 +- test/SemaCXX/warn-unreachable.cpp | 2 +- test/SemaObjC/warn-unreachable.m | 2 +- 9 files changed, 94 insertions(+), 31 deletions(-) diff --git a/include/clang/Analysis/Analyses/ReachableCode.h b/include/clang/Analysis/Analyses/ReachableCode.h index 14967ba298..08ee20930f 100644 --- a/include/clang/Analysis/Analyses/ReachableCode.h +++ b/include/clang/Analysis/Analyses/ReachableCode.h @@ -37,11 +37,19 @@ namespace clang { namespace clang { namespace reachable_code { +/// Classifications of unreachable code. +enum UnreachableKind { + UK_TrivialReturn, + UK_Break, + UK_Other +}; + class Callback { virtual void anchor(); public: virtual ~Callback() {} - virtual void HandleUnreachable(SourceLocation L, SourceRange R1, + virtual void HandleUnreachable(UnreachableKind UK, + SourceLocation L, SourceRange R1, SourceRange R2) = 0; }; diff --git a/include/clang/Basic/DiagnosticGroups.td b/include/clang/Basic/DiagnosticGroups.td index 97f0b3ed61..6bb101cfb6 100644 --- a/include/clang/Basic/DiagnosticGroups.td +++ b/include/clang/Basic/DiagnosticGroups.td @@ -424,6 +424,21 @@ def CharSubscript : DiagGroup<"char-subscripts">; def LargeByValueCopy : DiagGroup<"large-by-value-copy">; def DuplicateArgDecl : DiagGroup<"duplicate-method-arg">; +// Unreachable code warning groups. +// +// The goal is make -Wunreachable-code on by default, in -Wall, or at +// least actively used, with more noisy versions of the warning covered +// under separate flags. +// +def UnreachableCode : DiagGroup<"unreachable-code">; +def UnreachableCodeBreak : DiagGroup<"unreachable-code-break", + [UnreachableCode]>; +def UnreachableCodeTrivialReturn : DiagGroup<"unreachable-code-trivial-return", + [UnreachableCode]>; +def UnreachableCodeAggressive : DiagGroup<"unreachable-code-aggressive", + [UnreachableCodeBreak, + UnreachableCodeTrivialReturn]>; + // Aggregation warning settings. // -Widiomatic-parentheses contains warnings about 'idiomatic' diff --git a/include/clang/Basic/DiagnosticSemaKinds.td b/include/clang/Basic/DiagnosticSemaKinds.td index 7ac2fc1ec9..6cc177215f 100644 --- a/include/clang/Basic/DiagnosticSemaKinds.td +++ b/include/clang/Basic/DiagnosticSemaKinds.td @@ -359,8 +359,17 @@ def warn_suggest_noreturn_function : Warning< def warn_suggest_noreturn_block : Warning< "block could be declared with attribute 'noreturn'">, InGroup, DefaultIgnore; -def warn_unreachable : Warning<"will never be executed">, - InGroup>, DefaultIgnore; + +// Unreachable code. +def warn_unreachable : Warning< + "will never be executed">, + InGroup, DefaultIgnore; +def warn_unreachable_break : Warning< + "'break' will never be executed">, + InGroup, DefaultIgnore; +def warn_unreachable_trivial_return : Warning< + "'return' will never be executed">, + InGroup, DefaultIgnore; /// Built-in functions. def ext_implicit_lib_function_decl : ExtWarn< diff --git a/lib/Analysis/ReachableCode.cpp b/lib/Analysis/ReachableCode.cpp index 994f9d2a12..09b0efd0e6 100644 --- a/lib/Analysis/ReachableCode.cpp +++ b/lib/Analysis/ReachableCode.cpp @@ -59,9 +59,14 @@ static bool bodyEndsWithNoReturn(const CFGBlock::AdjacentBlock &AB) { return bodyEndsWithNoReturn(Pred); } -static bool isBreakPrecededByNoReturn(const CFGBlock *B, - const Stmt *S) { - if (!isa(S) || B->pred_empty()) +static bool isBreakPrecededByNoReturn(const CFGBlock *B, const Stmt *S, + reachable_code::UnreachableKind &UK) { + if (!isa(S)) + return false; + + UK = reachable_code::UK_Break; + + if (B->pred_empty()) return false; assert(B->empty()); @@ -131,23 +136,17 @@ static bool isTrivialExpression(const Expr *Ex) { isEnumConstant(Ex); } -static bool isTrivialReturnOrDoWhile(const CFGBlock *B, const Stmt *S) { - const Expr *Ex = dyn_cast(S); - - if (Ex && !isTrivialExpression(Ex)) - return false; - +static bool isTrivialReturnOrDoWhile(const CFGBlock *B, const Stmt *S, + reachable_code::UnreachableKind &UK) { // Check if the block ends with a do...while() and see if 'S' is the // condition. if (const Stmt *Term = B->getTerminator()) { - if (const DoStmt *DS = dyn_cast(Term)) - if (DS->getCond() == S) - return true; + if (const DoStmt *DS = dyn_cast(Term)) { + const Expr *Cond = DS->getCond(); + return Cond == S && isTrivialExpression(Cond); + } } - if (B->pred_size() != 1) - return false; - // Look to see if the block ends with a 'return', and see if 'S' // is a substatement. The 'return' may not be the last element in // the block because of destructors. @@ -155,17 +154,33 @@ static bool isTrivialReturnOrDoWhile(const CFGBlock *B, const Stmt *S) { I != E; ++I) { if (Optional CS = I->getAs()) { if (const ReturnStmt *RS = dyn_cast(CS->getStmt())) { + // Determine if we need to lock at the body of the block + // before the dead return. bool LookAtBody = false; - if (RS == S) + if (RS == S) { LookAtBody = true; + UK = reachable_code::UK_TrivialReturn; + } else { const Expr *RE = RS->getRetValue(); - if (RE && stripExprSugar(RE->IgnoreParenCasts()) == Ex) - LookAtBody = true; + if (RE) { + RE = stripExprSugar(RE->IgnoreParenCasts()); + if (RE == S) { + UK = reachable_code::UK_TrivialReturn; + LookAtBody = isTrivialExpression(RE); + } + } } - if (LookAtBody) + if (LookAtBody) { + // More than one predecessor? Restrict the heuristic + // to looking at return statements directly dominated + // by a noreturn call. + if (B->pred_size() != 1) + return false; + return bodyEndsWithNoReturn(*B->pred_begin()); + } } break; } @@ -588,19 +603,22 @@ static SourceLocation GetUnreachableLoc(const Stmt *S, void DeadCodeScan::reportDeadCode(const CFGBlock *B, const Stmt *S, clang::reachable_code::Callback &CB) { + // The kind of unreachable code found. + reachable_code::UnreachableKind UK = reachable_code::UK_Other; + // Suppress idiomatic cases of calling a noreturn function just // before executing a 'break'. If there is other code after the 'break' // in the block then don't suppress the warning. - if (isBreakPrecededByNoReturn(B, S)) + if (isBreakPrecededByNoReturn(B, S, UK)) return; // Suppress trivial 'return' statements that are dead. - if (isTrivialReturnOrDoWhile(B, S)) + if (UK == reachable_code::UK_Other && isTrivialReturnOrDoWhile(B, S, UK)) return; SourceRange R1, R2; SourceLocation Loc = GetUnreachableLoc(S, R1, R2); - CB.HandleUnreachable(Loc, R1, R2); + CB.HandleUnreachable(UK, Loc, R1, R2); } //===----------------------------------------------------------------------===// diff --git a/lib/Sema/AnalysisBasedWarnings.cpp b/lib/Sema/AnalysisBasedWarnings.cpp index dabac1e6c4..d49dfd5845 100644 --- a/lib/Sema/AnalysisBasedWarnings.cpp +++ b/lib/Sema/AnalysisBasedWarnings.cpp @@ -65,9 +65,22 @@ namespace { public: UnreachableCodeHandler(Sema &s) : S(s) {} - void HandleUnreachable(SourceLocation L, SourceRange R1, + void HandleUnreachable(reachable_code::UnreachableKind UK, + SourceLocation L, SourceRange R1, SourceRange R2) override { - S.Diag(L, diag::warn_unreachable) << R1 << R2; + unsigned diag = diag::warn_unreachable; + switch (UK) { + case reachable_code::UK_Break: + diag = diag::warn_unreachable_break; + break; + case reachable_code::UK_TrivialReturn: + diag = diag::warn_unreachable_trivial_return; + break; + case reachable_code::UK_Other: + break; + } + + S.Diag(L, diag) << R1 << R2; } }; } diff --git a/test/Sema/warn-unreachable.c b/test/Sema/warn-unreachable.c index 2334c37381..663fab0f3c 100644 --- a/test/Sema/warn-unreachable.c +++ b/test/Sema/warn-unreachable.c @@ -1,4 +1,4 @@ -// RUN: %clang_cc1 %s -fsyntax-only -verify -fblocks -Wunreachable-code -Wno-unused-value -Wno-covered-switch-default -I %S/Inputs +// RUN: %clang_cc1 %s -fsyntax-only -verify -fblocks -Wunreachable-code-aggressive -Wno-unused-value -Wno-covered-switch-default -I %S/Inputs #include "warn-unreachable.h" diff --git a/test/SemaCXX/unreachable-code.cpp b/test/SemaCXX/unreachable-code.cpp index b6b8ab4209..5016c3f24b 100644 --- a/test/SemaCXX/unreachable-code.cpp +++ b/test/SemaCXX/unreachable-code.cpp @@ -1,4 +1,4 @@ -// RUN: %clang_cc1 -fcxx-exceptions -fexceptions -fsyntax-only -Wunreachable-code -fblocks -verify %s +// RUN: %clang_cc1 -fcxx-exceptions -fexceptions -fsyntax-only -Wunreachable-code-aggressive -fblocks -verify %s int j; int bar(); diff --git a/test/SemaCXX/warn-unreachable.cpp b/test/SemaCXX/warn-unreachable.cpp index 49d26daa2f..843720fa5f 100644 --- a/test/SemaCXX/warn-unreachable.cpp +++ b/test/SemaCXX/warn-unreachable.cpp @@ -1,4 +1,4 @@ -// RUN: %clang_cc1 %s -fcxx-exceptions -fexceptions -fsyntax-only -verify -fblocks -Wunreachable-code -Wno-unused-value +// RUN: %clang_cc1 %s -fcxx-exceptions -fexceptions -fsyntax-only -verify -fblocks -Wunreachable-code-aggressive -Wno-unused-value int &halt() __attribute__((noreturn)); int &live(); diff --git a/test/SemaObjC/warn-unreachable.m b/test/SemaObjC/warn-unreachable.m index e2ce8a7110..979b9053b3 100644 --- a/test/SemaObjC/warn-unreachable.m +++ b/test/SemaObjC/warn-unreachable.m @@ -1,4 +1,4 @@ -// RUN: %clang %s -fsyntax-only -Xclang -verify -fblocks -Wunreachable-code -Wno-unused-value -Wno-covered-switch-default +// RUN: %clang %s -fsyntax-only -Xclang -verify -fblocks -Wunreachable-code-aggressive -Wno-unused-value -Wno-covered-switch-default // This previously triggered a warning from -Wunreachable-code because of // a busted CFG. -- 2.40.0