some StmtExprs do not have side-effects

Differential Revision: http://reviews.llvm.org/D10211

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@239476 91177308-0d34-0410-b5e6-96231b3b80d8

include/clang/AST/EvaluatedExprVisitor.h

@@ -28,6 +28,7 @@ class ASTContext;
 /// of its potentially-evaluated subexpressions, recursively.
 template<template <typename> class Ptr, typename ImplClass>
 class EvaluatedExprVisitorBase : public StmtVisitorBase<Ptr, ImplClass, void> {
+protected:
   const ASTContext &Context;
 
 public:

lib/AST/Expr.cpp

@@ -2887,6 +2887,28 @@ bool Expr::isConstantInitializer(ASTContext &Ctx, bool IsForRef,
   return false;
 }
 
+namespace {
+  /// \brief Look for any side effects within a Stmt.
+  class SideEffectFinder : public ConstEvaluatedExprVisitor<SideEffectFinder> {
+    typedef ConstEvaluatedExprVisitor<SideEffectFinder> Inherited;
+    const bool IncludePossibleEffects;
+    bool HasSideEffects;
+
+  public:
+    explicit SideEffectFinder(const ASTContext &Context, bool IncludePossible)
+      : Inherited(Context),
+        IncludePossibleEffects(IncludePossible), HasSideEffects(false) { }
+
+    bool hasSideEffects() const { return HasSideEffects; }
+
+    void VisitExpr(const Expr *E) {
+      if (!HasSideEffects &&
+          E->HasSideEffects(Context, IncludePossibleEffects))
+        HasSideEffects = true;
+    }
+  };
+}
+
 bool Expr::HasSideEffects(const ASTContext &Ctx,
                           bool IncludePossibleEffects) const {
   // In circumstances where we care about definite side effects instead of
@@ -2974,7 +2996,6 @@ bool Expr::HasSideEffects(const ASTContext &Ctx,
   case CompoundAssignOperatorClass:
   case VAArgExprClass:
   case AtomicExprClass:
-  case StmtExprClass:
   case CXXThrowExprClass:
   case CXXNewExprClass:
   case CXXDeleteExprClass:
@@ -2982,6 +3003,13 @@ bool Expr::HasSideEffects(const ASTContext &Ctx,
     // These always have a side-effect.
     return true;
 
+  case StmtExprClass: {
+    // StmtExprs have a side-effect if any substatement does.
+    SideEffectFinder Finder(Ctx, IncludePossibleEffects);
+    Finder.Visit(cast<StmtExpr>(this)->getSubStmt());
+    return Finder.hasSideEffects();
+  }
+
   case ParenExprClass:
   case ArraySubscriptExprClass:
   case MemberExprClass:

test/Sema/stmtexprs.c

@@ -0,0 +1,9 @@
+// RUN: %clang_cc1 %s -verify -pedantic -fsyntax-only -Wno-gnu-statement-expression
+
+int stmtexpr_fn();
+void stmtexprs(int i) {
+  __builtin_assume( ({ 1; }) ); // no warning about "side effects"
+  __builtin_assume( ({ if (i) { (void)0; }; 42; }) ); // no warning about "side effects"
+  // expected-warning@+1 {{the argument to '__builtin_assume' has side effects that will be discarded}}
+  __builtin_assume( ({ if (i) ({ stmtexpr_fn(); }); 1; }) );
+}