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Further refine -Wunreachable-code groups so that -Wno-unreachable-code-break doesn't turn off all unreachable code warnings.

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Also relax unreachable 'break' and 'return' to not check for being
preceded by a call to 'noreturn'.  That turns out to not be so
interesting in practice.

llvm-svn: 204000
This commit is contained in:
Ted Kremenek
2014-03-15 05:47:06 +00:00
parent fb6b25b5e4
commit ad8753c00e
6 changed files with 104 additions and 63 deletions
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61
clang/lib/Analysis/ReachableCode.cpp
View File

@@ -136,8 +136,7 @@ static bool isTrivialExpression(const Expr *Ex) {
isEnumConstant(Ex);
}
static bool isTrivialReturnOrDoWhile(const CFGBlock *B, const Stmt *S,
reachable_code::UnreachableKind &UK) {
static bool isTrivialDoWhile(const CFGBlock *B, const Stmt *S) {
// Check if the block ends with a do...while() and see if 'S' is the
// condition.
if (const Stmt *Term = B->getTerminator()) {
@@ -146,7 +145,10 @@ static bool isTrivialReturnOrDoWhile(const CFGBlock *B, const Stmt *S,
return Cond == S && isTrivialExpression(Cond);
}
}
return false;
}
static bool isTrivialReturn(const CFGBlock *B, const Stmt *S) {
// 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.
@@ -156,30 +158,11 @@ static bool isTrivialReturnOrDoWhile(const CFGBlock *B, const Stmt *S,
if (const ReturnStmt *RS = dyn_cast<ReturnStmt>(CS->getStmt())) {
// Determine if we need to lock at the body of the block
// before the dead return.
bool LookAtBody = false;
if (RS == S) {
LookAtBody = true;
UK = reachable_code::UK_TrivialReturn;
}
else {
const Expr *RE = RS->getRetValue();
if (RE) {
RE = stripExprSugar(RE->IgnoreParenCasts());
if (RE == S) {
UK = reachable_code::UK_TrivialReturn;
LookAtBody = isTrivialExpression(RE);
}
}
}
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());
if (RS == S)
return true;
if (const Expr *RE = RS->getRetValue()) {
RE = stripExprSugar(RE->IgnoreParenCasts());
return RE == S && isTrivialExpression(RE);
}
}
break;
@@ -606,15 +589,25 @@ void DeadCodeScan::reportDeadCode(const CFGBlock *B,
// 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, UK))
return;
do {
// 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 (isa<BreakStmt>(S)) {
UK = reachable_code::UK_Break;
break;
}
// Suppress trivial 'return' statements that are dead.
if (UK == reachable_code::UK_Other && isTrivialReturnOrDoWhile(B, S, UK))
return;
if (isTrivialDoWhile(B, S))
return;
// Suppress trivial 'return' statements that are dead.
if (isTrivialReturn(B, S)) {
UK = reachable_code::UK_TrivialReturn;
break;
}
} while(false);
SourceRange R1, R2;
SourceLocation Loc = GetUnreachableLoc(S, R1, R2);