Don't warn about unused values in ternary ?: expressions unless both the LHS and...

Patch by Justin Bogner!  Fixes PR 8282.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@126779 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/AST/Expr.cpp b/lib/AST/Expr.cpp
index 8e44c073682bf44bbb4b83cf9ae1ab3f9a658aba..930457c249c295a44002f91ac87e6f4ae7c57861 100644 (file)
--- a/lib/AST/Expr.cpp
+++ b/lib/AST/Expr.cpp
@@ -1404,13 +1404,15 @@ bool Expr::isUnusedResultAWarning(SourceLocation &Loc, SourceRange &R1,
     return false;
 
   case ConditionalOperatorClass: {
-    // The condition must be evaluated, but if either the LHS or RHS is a
-    // warning, warn about them.
+    // If only one of the LHS or RHS is a warning, the operator might
+    // be being used for control flow. Only warn if both the LHS and
+    // RHS are warnings.
     const ConditionalOperator *Exp = cast<ConditionalOperator>(this);
-    if (Exp->getLHS() &&
-        Exp->getLHS()->isUnusedResultAWarning(Loc, R1, R2, Ctx))
+    if (!Exp->getRHS()->isUnusedResultAWarning(Loc, R1, R2, Ctx))
+      return false;
+    if (!Exp->getLHS())
       return true;
-    return Exp->getRHS()->isUnusedResultAWarning(Loc, R1, R2, Ctx);
+    return Exp->getLHS()->isUnusedResultAWarning(Loc, R1, R2, Ctx);
   }
 
   case MemberExprClass:

diff --git a/test/Sema/warn-unused-value.c b/test/Sema/warn-unused-value.c
index 876eb9e4823e563e4855b6c38e99b43ba8e7a104..95cd8fb7040027b5aee885a1c8cea9d617b310aa 100644 (file)
--- a/test/Sema/warn-unused-value.c
+++ b/test/Sema/warn-unused-value.c
@@ -72,6 +72,15 @@ int test_logical_bar() {
   return x;
 }
 
+// PR8282
+void conditional_for_control_flow(int cond, int x, int y)
+{
+    cond? y++ : x; // no-warning
+    cond? y : ++x; // no-warning
+    cond? (x |= y) : ++x; // no-warning
+    cond? y : x; // expected-warning {{expression result unused}}
+}
+
 struct s0 { int f0; };
 
 void f0(int a);