[-Wunreachable-code] Don't warn about trivially unreachable return statements preceded by 'noreturn' functions.
llvm-svn: 202352
diff --git a/clang/lib/Analysis/ReachableCode.cpp b/clang/lib/Analysis/ReachableCode.cpp
index 046c9f4..797e02e 100644
--- a/clang/lib/Analysis/ReachableCode.cpp
+++ b/clang/lib/Analysis/ReachableCode.cpp
@@ -262,6 +262,12 @@
return false;
}
+static bool bodyEndsWithNoReturn(const CFGBlock::AdjacentBlock &AB) {
+ const CFGBlock *Pred = AB.getPossiblyUnreachableBlock();
+ assert(!AB.isReachable() && Pred);
+ return bodyEndsWithNoReturn(Pred);
+}
+
static bool isBreakPrecededByNoReturn(const CFGBlock *B,
const Stmt *S) {
if (!isa<BreakStmt>(S) || B->pred_empty())
@@ -269,10 +275,53 @@
assert(B->empty());
assert(B->pred_size() == 1);
- const CFGBlock::AdjacentBlock &AB = *B->pred_begin();
- const CFGBlock *Pred = AB.getPossiblyUnreachableBlock();
- assert(!AB.isReachable() && Pred);
- return bodyEndsWithNoReturn(Pred);
+ return bodyEndsWithNoReturn(*B->pred_begin());
+}
+
+static bool isEnumConstant(const Expr *Ex) {
+ const DeclRefExpr *DR = dyn_cast<DeclRefExpr>(Ex);
+ if (!DR)
+ return false;
+ return isa<EnumConstantDecl>(DR->getDecl());
+}
+
+static bool isTrivialExpression(const Expr *Ex) {
+ return isa<IntegerLiteral>(Ex) || isa<StringLiteral>(Ex) ||
+ isEnumConstant(Ex);
+}
+
+static bool isTrivialReturnPrecededByNoReturn(const CFGBlock *B,
+ const Stmt *S) {
+ if (B->pred_empty())
+ return false;
+
+ const Expr *Ex = dyn_cast<Expr>(S);
+ if (!Ex)
+ return false;
+
+ Ex = Ex->IgnoreParenCasts();
+
+ if (!isTrivialExpression(Ex))
+ 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.
+ assert(!B->empty());
+ for (CFGBlock::const_reverse_iterator I = B->rbegin(), E = B->rend();
+ I != E; ++I) {
+ if (Optional<CFGStmt> CS = I->getAs<CFGStmt>()) {
+ if (const ReturnStmt *RS = dyn_cast<ReturnStmt>(CS->getStmt())) {
+ const Expr *RE = RS->getRetValue();
+ if (RE && RE->IgnoreParenCasts() == Ex)
+ break;
+ }
+ return false;
+ }
+ }
+
+ assert(B->pred_size() == 1);
+ return bodyEndsWithNoReturn(*B->pred_begin());
}
void DeadCodeScan::reportDeadCode(const CFGBlock *B,
@@ -284,6 +333,10 @@
if (isBreakPrecededByNoReturn(B, S))
return;
+ // Suppress trivial 'return' statements that are dead.
+ if (isTrivialReturnPrecededByNoReturn(B, S))
+ return;
+
// Was this an unreachable 'default' case? Such cases are covered
// by -Wcovered-switch-default, if the user so desires.
const Stmt *Label = B->getLabel();